JPH11177175A - Nitride semiconductor device - Google Patents

Abstract

(57) Abstract: A long-term continuous oscillation is realized by lowering the threshold current and voltage of an LD element made of a nitride semiconductor. An active layer includes an n-conductive side nitride semiconductor layer and a p-type nitride semiconductor layer.
A nitride semiconductor element formed between the conductive-side nitride semiconductor layer and the n-side and / or p-conductive side nitride semiconductor layer, the position being apart from the active layer;
Alternatively, an n-side strained superlattice layer in which first and second nitride semiconductor layers having different band gap energies and different impurity concentrations from each other are stacked is provided at a contact position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element such as an LED (light emitting diode), an LD (laser diode) or a superluminescent diode (SLD), a light receiving element such as a solar cell or an optical sensor, or a transistor. Nitride semiconductors used for electronic devices such as power devices (In _X Al _Y Ga _{1 -XYN} , 0 ≦ X, 0 ≦ Y, X +
Y <1). Note that the general formulas In _x Ga _1-x N, Al _y Ga _1-y N, and the like used in the present specification simply indicate the composition formula of the nitride semiconductor layer, and different layers have the same composition formula, for example. However, this does not mean that the X and Y values of those layers match.

[0002]

2. Description of the Related Art Nitride semiconductors have just recently been put to practical use in full-color LED displays, traffic signals and the like as materials for high-brightness blue LEDs and pure green LEDs. LEDs used for these various devices have a single quantum well structure (SQW: Sing) having a well layer made of InGaN.
le-Quantum-Well) or multiple quantum well structure (MQ
The active layer of W (Multi-Quantum-Well) has a double hetero structure sandwiched between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. Wavelengths of blue and green are InGaN
It is determined by increasing or decreasing the In composition ratio of the well layer.

In addition, the present applicant recently announced the world's first laser oscillation of 410 nm at room temperature under pulse current using this material {for example, Jpn. J. Appl. Phys. 35 (1996) L
74, Jpn. J. Appl. Phys. 35 (1996) L217}. This laser device has a double heterostructure having an active layer of a multiple quantum well structure using a well layer made of InGaN, and has a threshold current 610 under a condition of a pulse width of 2 μs and a pulse period of 2 ms.
It shows an oscillation of 410 nm at mA, a threshold current density of 8.7 kA / cm ² . In addition, we have improved the laser device in Appl.P.
hys. Lett. 69 (1996) 1477. This laser device has a structure in which a ridge stripe is formed in a part of a p-type nitride semiconductor layer, has a pulse width of 1 μs, a pulse period of 1 ms, a duty ratio of 0.1%, and has a threshold current of 1%.
It shows oscillation at 87 mA, a threshold current density of 3 kA / cm ² and 410 nm. And we also succeeded and announced for the first time continuous oscillation at room temperature. {For example, Nikkei Electronics December 2, 1996 Technical Bulletin, Appl.Phys. Lett. 69 (1
996) 3034, Appl. Phys. Lett. 69 (1996) 4056 et al.], The laser device has a threshold current density of 3.6 kA /
cm ² , 5.5 V threshold voltage, 1.5 mW output, 2
7 shows continuous oscillation for 7 hours.

[0004]

The blue and green LEDs made of a nitride semiconductor have a forward current (If) of 20 mA, a forward voltage (Vf) of 3.4 V to 3.6 V, and a GaAl.
Since it is higher than a red LED made of an As-based semiconductor by 2 V or more, further reduction in Vf is desired. Also, L
In the case of D, the current and voltage at the threshold are still high, and in order to continuously oscillate at room temperature for a long time, it is necessary to realize a more efficient device in which the threshold current and voltage are lowered.

If the threshold voltage of the laser element can be reduced, if the technology is applied to an LED element,
A decrease in Vf of the device can be expected. Therefore, an object of the present invention is to realize long-term continuous oscillation by lowering the current and voltage at the threshold value of an LD element mainly composed of a nitride semiconductor.

[0006]

SUMMARY OF THE INVENTION According to the present invention, in a nitride semiconductor device, at least one semiconductor layer other than the active layer has a strained superlattice structure to improve the crystallinity of the semiconductor layer. Have been completed by finding that the electric resistance of the semiconductor layer can be reduced. That is, in the first nitride semiconductor device of the present invention, the active layer has a nitride semiconductor layer on the n-conductive side (hereinafter, referred to as n-side) and a nitride semiconductor on the p-conductive side (hereinafter, referred to as p-side). A nitride semiconductor element formed between the active layer and the n-conductive side nitride semiconductor layer, the band gap energies differ from each other at a position apart from or in contact with the active layer, and First and second different n-type impurity concentrations
Characterized by having an n-side strained superlattice layer formed by laminating a nitride semiconductor layer of Thus, the electric resistance of the nitride semiconductor layer formed of the superlattice layer can be reduced, so that the overall resistance of the n-conductive side nitride semiconductor layer can be reduced.

A second nitride semiconductor device according to the present invention comprises:
An active layer is a nitride semiconductor device formed between an n-conductive side nitride semiconductor layer and a p-conductive side nitride semiconductor layer. A p-side strained superlattice layer in which third and fourth nitride semiconductor layers having different band gap energies and different p-type impurity concentrations from each other are stacked at a position separated from or in contact with the layer; It is characterized by the following. Thus, the electric resistance of the nitride semiconductor layer formed of the superlattice layer can be reduced, so that the overall resistance of the p-conductive side nitride semiconductor layer can be reduced. Here, the p-conducting side refers to a nitride semiconductor layer between the active layer and the positive electrode (p-electrode), and the n-conducting side refers to a nitride on the opposite side of the active layer from the p-conducting side. It refers to a semiconductor layer. In addition,
It goes without saying that the order of lamination of the first nitride semiconductor layer and the second nitride semiconductor layer and the order of lamination of the third nitride semiconductor layer and the fourth nitride semiconductor layer do not matter.

A third nitride semiconductor device according to the present invention is a nitride semiconductor device in which an active layer is formed between an n-conductive side nitride semiconductor layer and a p-conductive side nitride semiconductor layer. In the nitride semiconductor layer on the n-conductive side,
An n-side strained superlattice layer in which first and second nitride semiconductor layers having different band gap energies and different n-type impurity concentrations from each other are stacked at a position separated from or in contact with the active layer. A third and a fourth nitride semiconductor layer having different band gap energies and different p-type impurity concentrations from each other at a position separated from or in contact with the active layer in the nitride semiconductor layer on the p-conductive side. And a p-side strained superlattice layer formed by laminating an object semiconductor layer. Thus, the electrical resistance of the nitride semiconductor layer formed of the superlattice layer can be reduced, so that the overall resistance of the nitride semiconductor layers on the n-conductive side and the p-conductive side can be reduced.

In the first or third nitride semiconductor device of the present invention, the n-side strained superlattice layer may be a buffer formed in contact with the substrate if the photoelectric conversion device is, for example, a light emitting device or a light receiving device. Layer, an n-side contact layer on which an n-electrode is formed,
It is formed as at least one of an n-side cladding layer for confining carriers and an n-side light guide layer for guiding light emission of the active layer. In the second or third nitride semiconductor device, the p-side strained superlattice layer is a p-side contact layer on which a p-electrode is formed, a p-side cladding layer for confining carriers, and a p-side waveguide for guiding light emission of the active layer. It is formed as at least one layer of the side light guide layers.

In the first and third nitride semiconductor devices of the present invention, the impurity concentration of the first nitride semiconductor layer having a large band gap energy in the superlattice layer is changed to the second nitride semiconductor layer having a small band gap energy. May be increased or decreased as compared with the impurity concentration. When the impurity concentration of the first nitride semiconductor layer is higher than the impurity concentration of the second nitride semiconductor layer,
Carriers can be generated in the first nitride semiconductor layer having a large bandgap energy and injected into the second nitride semiconductor layer having a small bandgap energy. Can be moved by the nitride semiconductor layer, so that the electric resistance of the superlattice layer can be reduced. Here, in this specification, when the n-side strain superlattice layer and the p-side strain superlattice layer are collectively referred to, they are simply referred to as a superlattice layer as described above.

In the first nitride semiconductor device, when the impurity concentration of the first nitride semiconductor layer is higher than the impurity concentration of the second nitride semiconductor layer, In the nitride semiconductor layer described above, the n-type or p-type impurity concentration of a portion close to the second nitride semiconductor layer (hereinafter referred to as a close portion) is compared with a portion remote from the second nitride semiconductor layer. It is preferable to make it smaller. This can prevent carriers moving in the second nitride semiconductor layer from being scattered by impurities in the adjacent portion, and
The mobility of the second nitride semiconductor layer can be further increased, and the electric resistance of the superlattice layer can be further reduced.

Specifically, the first and third nitride semiconductor elements
In the element, the first having a large band gap energy
When the nitride semiconductor layer is heavily doped with n-type impurities,
N type impurity concentration of 1 nitride semiconductor layer is 1 × 10¹⁷/cm
^Three~ 1 × 10²⁰/cm^ThreeAnd the second nitride semiconductor
The n-type impurity concentration of the layer is lower than that of the first nitride semiconductor layer
Kukatsu 1 × 10¹⁹/cm^ThreePreferably set to
No. Note that the second nitride having a small band gap energy is used.
The n-type impurity concentration of the product semiconductor layer is 1 × 10¹⁸/cm ^ThreeLess than
More preferably 1 × 10¹⁷/cm^ThreeBelow
More preferably. That is, the second nitride semiconductor
From the viewpoint of increasing the mobility of the layer, the second nitride semiconductor
The smaller the n-type impurity concentration of the layer, the better.
Undoped (undoped) layer of nitride semiconductor layer
That is, it is most desirable that the impurity is not intentionally doped.

Further, when the impurity concentration of the first nitride semiconductor layer is lower than that of the second nitride semiconductor layer, the first nitride semiconductor layer has It is preferable that the n-type impurity concentration in a portion close to the nitride semiconductor layer be lower than that in a portion away from the first nitride semiconductor layer. Further, when the impurity concentration of the first nitride semiconductor layer is lower than that of the second nitride semiconductor layer, the n-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁹ / Cm ³ or less, and the n-type impurity concentration of the second nitride semiconductor layer is 1 ×
It is preferably in the range of 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ . The first nitride semiconductor layer preferably has a thickness of 1
× 10 ¹⁸ / cm ³ or less, more preferably 1 × 10 ¹⁷ / cm ³
cm ³ or less, most preferably undoped
e), that is, a state in which impurities are not intentionally doped is most desirable.

In the first and third nitride semiconductor devices, in order to form a superlattice layer having good crystallinity in the superlattice layer, the first nitride semiconductor layer has a relatively high energy band gap. The second nitride semiconductor layer is formed of Al _Y Ga ₁ -YN (0 <Y <1) capable of growing a large and highly crystalline layer. It is preferable to form In _x Ga ₁ -xN (0 ≦ X <1) which can grow a good layer.

Further, in the first and third nitride semiconductor devices, in the superlattice layer, the second nitride semiconductor layer is formed of G
More preferably, it consists of aN. Thereby, the first nitride semiconductor layer (Al _Y Ga ₁ -YN) and the second nitride semiconductor layer (GaN) can be grown in the same atmosphere, so that the superlattice layer It is extremely advantageous in manufacturing.

In the first and third nitride semiconductor devices, in the superlattice layer, the first nitride semiconductor layer is made of A
1 _x Ga _{1 -x} N (0 <X <1), and the second nitride semiconductor layer may be formed of Al _Y Ga ₁ -YN (0 <Y <1, X> Y). it can.

It is further preferable that the first nitride semiconductor layer or the second nitride semiconductor layer is not doped with an n-type impurity.

In the second and third nitride semiconductor devices of the present invention, the impurity concentration of the third nitride semiconductor layer having a large band gap energy in the superlattice layer is changed to the fourth nitride semiconductor layer having a small band gap energy. May be increased or decreased as compared with the impurity concentration. When the impurity concentration of the third nitride semiconductor layer is higher than the impurity concentration of the fourth nitride semiconductor layer,
Carriers can be generated in the third nitride semiconductor layer having a large band gap energy and injected into the fourth nitride semiconductor layer having a small band gap energy, and the injected carriers can be injected into the fourth nitride semiconductor layer having a small impurity concentration and a high mobility. Can be moved by the nitride semiconductor layer, so that the electric resistance of the superlattice layer can be reduced.

In the second and third nitride semiconductor devices, when the impurity concentration of the third nitride semiconductor layer is higher than the impurity concentration of the fourth nitride semiconductor layer,
In the first nitride semiconductor layer of the superlattice layer, a portion close to the fourth nitride semiconductor layer (hereinafter, referred to as a close portion).
It is preferable that the p-type impurity concentration is lower than that of a portion remote from the fourth nitride semiconductor layer. This can prevent carriers moving in the fourth nitride semiconductor layer from being scattered by impurities in the adjacent portion, and
The mobility of the fourth nitride semiconductor layer can be further increased, and the electric resistance of the superlattice layer can be further reduced.

In the second and third nitride semiconductor devices, when the impurity concentration of the third nitride semiconductor layer is higher than the impurity concentration of the fourth nitride semiconductor layer, the band gap energy Is large, the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ¹⁸ / cm ³ to 1 × 10
²¹ / cm ³ , and the p-type impurity concentration of the fourth nitride semiconductor layer is set to be lower than the impurity concentration of the third nitride semiconductor layer and 1 × 10 ²⁰ / cm ³ or less. preferable. Note that the fourth nitride semiconductor layer having a small band gap energy is more preferably 1 × 10 ¹⁹ / cm ³ or less, further preferably 1 × 10 ¹⁸ / cm ³ or less. That is, from the viewpoint of increasing the mobility of the fourth nitride semiconductor layer, the lower the p-type impurity concentration of the fourth nitride semiconductor layer, the better, and the fourth nitride semiconductor layer may be an undoped layer, that is, It is most desirable that the impurity is not intentionally doped.

In the second and third nitride semiconductor devices, the third nitride semiconductor layer has an impurity concentration of
When the impurity concentration of the fourth nitride semiconductor layer is smaller than that of the third nitride semiconductor layer, the p-type impurity concentration of a portion of the fourth nitride semiconductor layer adjacent to the third nitride semiconductor layer is reduced to the third nitride semiconductor layer. It is preferable that the size be smaller than that of a portion remote from the semiconductor layer.

In the second and third nitride semiconductor devices, the third nitride semiconductor layer may have an impurity concentration of
When the impurity concentration of the third nitride semiconductor layer is smaller than that of the third nitride semiconductor layer, the p-type impurity concentration of the third nitride semiconductor layer is 1 ×
It is preferably 10 ²⁰ / cm ³ or less and the p-type impurity concentration of the fourth nitride semiconductor layer is in the range of 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²¹ / cm ³ . Incidentally, the third nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³ or less, more preferably 1 × 10 ¹⁹ / cm ³ or less.
0 ¹⁸ / cm ³ or less, most preferably undoped (und)
ope), that is, a state in which impurities are not intentionally doped.

In the second and third nitride semiconductor devices, in order to form a superlattice layer having good crystallinity, the third nitride semiconductor layer has a relatively large energy band gap and a high crystallinity. A good layer can be grown by Al _Y Ga _1-Y N (0 <Y <1), and the fourth nitride semiconductor layer is formed by In _X Ga _1-X N (0 ≦ X <1). Preferably, it is formed. The fourth nitride semiconductor layer is composed of G
More preferably, it consists of aN. Thereby, the third nitride semiconductor layer (Al _Y Ga ₁ -YN) and the fourth nitride semiconductor layer (GaN) can be grown in the same atmosphere. It is extremely advantageous in manufacturing.

Further, in the second and third nitride semiconductor devices, the third nitride semiconductor layer is formed of Al _x Ga ₁ -xN
(0 <X <1), and the fourth nitride semiconductor layer may be formed of Al _Y Ga _1-Y N (0 <Y <1, X> Y).

In the second and third nitride semiconductor devices, it is preferable that the third nitride semiconductor layer or the fourth nitride semiconductor layer is not doped with a p-type impurity.

In the third nitride semiconductor device, the n-side strain
In the first superlattice layer,
The gap energy of the second nitride semiconductor layer.
Greater than the first gap energy and the first nitrogen
The n-type impurity concentration of the nitride semiconductor layer is the second nitride semiconductor.
Higher than the n-type impurity concentration of the body layer and the p-side strain
In the superlattice layer, the band of the third nitride semiconductor layer
The gap energy of the fourth nitride semiconductor layer
Greater than the gap energy and the third nitriding
The p-type impurity concentration of the nitride semiconductor layer is the fourth nitride semiconductor.
It can be set higher than the p-type impurity concentration of the layer. This
In the case, the n-type impurity concentration of the first nitride semiconductor layer is
1 × 10¹⁷/cm^Three~ 1 × 10²⁰/cm^ThreeIn the range
2 has an n-type impurity concentration of 1 × 10¹⁹/cm
^ThreeAnd the p-type impurity of the third nitride semiconductor layer
Pure substance concentration is 1 × 10¹⁸/cm^Three~ 1 × 10^{twenty one}/cm^ThreeIn the range
And the p-type impurity concentration of the fourth nitride semiconductor layer is
1 × 10^{Two 0}/cm^ThreeThe following is preferred.

In the third nitride semiconductor device, in the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and the second N larger than the nitride semiconductor layer of
And in the p-side strained superlattice layer, the third nitride semiconductor layer comprises:
The fourth nitride semiconductor layer may be set to have a band gap energy larger than that of the fourth nitride semiconductor layer and a p-type impurity concentration smaller than that of the fourth nitride semiconductor layer. In this case, the n-type impurity concentration of the first nitride semiconductor layer is 1
In the range of × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ ,
N type impurity concentration of the nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³
And the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ²⁰ / cm ³ or less, and the p-type impurity concentration of the fourth nitride semiconductor layer is 1 × 10 ¹⁸ / cm ^3. / Cm ³ 〜
It is preferably in the range of 1 × 10 ²¹ / cm ³ .

Further, in the third nitride semiconductor device, in the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and the second N smaller than the nitride semiconductor layer of
The p-side strained superlattice layer, the third nitride semiconductor layer has a bandgap energy larger than that of the fourth nitride semiconductor layer and the fourth nitride semiconductor layer It can be set to have a higher p-type impurity concentration. In this case, the n-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³ or less, and the n-type impurity concentration of the second nitride semiconductor layer is 1 × 10 ¹⁷ / cm ^3. And the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ²⁰ / cm ^3.
In the range of 10 ¹⁸ / cm ³ to 1 × 10 ²¹ / cm ³ , wherein the p-type impurity concentration of the fourth nitride semiconductor layer is 1 × 10 ²⁰ / cm 3
It is preferably ³ or less.

Further, in the third nitride semiconductor device, in the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and the second Having a lower n-type impurity concentration than the nitride semiconductor layer of the above, and in the p-side strained superlattice layer, the third nitride semiconductor layer has a band gap energy larger than that of the fourth nitride semiconductor layer. The p-type impurity concentration may be set to be smaller than that of the fourth nitride semiconductor layer. In this case, the first
N type impurity concentration of the nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³
Wherein the n-type impurity concentration of the second nitride semiconductor layer is in the range of 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ and the p-type impurity of the third nitride semiconductor layer is Mold impurity concentration is 1
× 10 ²⁰ / cm ³ or less, and the p of the fourth nitride semiconductor layer
The mold impurity concentration is preferably in the range of 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²¹ / cm ³ .

In the third nitride semiconductor device, in the n-side strained superlattice layer, the first nitride semiconductor layer is formed of Al
_Y Ga _1-Y N (0 <Y <1), the second nitride semiconductor layer is formed of In _x Ga _1-X N (0 ≦ X <1), and the p-side strain exceeds In the lattice layer, the third nitride semiconductor layer is formed of Al _Y Ga _1-Y N (0 <Y <1), and the fourth nitride semiconductor layer is formed of In _X Ga _1-X N (0 ≦ Y). X <
It can be formed in 1). Further, the second and fourth
Are preferably made of GaN.

In the third nitride semiconductor device, in the n-side strain superlattice layer, the first nitride semiconductor layer is formed of Al
_X Ga _1-X N (0 <X <1); the second nitride semiconductor layer is formed of Al _Y Ga _1-Y N (0 <Y <1, X>Y); In the side strain superlattice layer, the third nitride semiconductor layer is formed of Al _x Ga ₁ -xN (0 <X <1);
The fourth nitride semiconductor layer is composed of Al _Y Ga _{1 -Y} N (0 <Y <
1, X> Y).

Further, in the third nitride semiconductor device, the first nitride semiconductor layer or the second nitride semiconductor layer is preferably an undoped layer not doped with an n-type impurity. It is preferable that the third nitride semiconductor layer or the fourth nitride semiconductor layer is an undoped layer not doped with a p-type impurity.

In the first, second and third nitride semiconductor devices, the active layer preferably includes an InGaN layer,
More preferably, the InGaN layer is a quantum well layer. The active layer may have a single quantum well structure or a multiple quantum well structure.

In one aspect of the present invention, the nitride semiconductor device is a laser oscillation device wherein the active layer is located between a p-side cladding layer and an n-side cladding layer, and At least one of the n-side cladding layers is the n-side strain superlattice layer or the p-side strain superlattice layer. Thereby, a laser oscillation element having a low threshold current can be configured.

In the laser oscillation device, at least one of the region between the p-side cladding layer and the active layer or the region between the p-side cladding layer and the active layer is made of a nitride semiconductor containing In or GaN. , Impurity concentration is 1 × 10 ¹⁹ / cm
It is preferable to form a light guide layer of ³ or less.
Since the light guide layer has a low absorptance of light generated in the active layer, the light emission of the active layer is hardly attenuated, and a laser device capable of oscillating with low gain can be realized. In the present invention, in order to reduce the light absorptivity, the impurity concentration of the light guide layer is more preferably 1 × 10 ¹⁸ / cm ³ or less, and further preferably 1 × 10 ¹⁷ / cm ³ or less. Preferably, it is most preferably undoped. The light guide layer may have a super lattice structure.

Further, a nitride semiconductor having a thickness of 0.1 μm or less having a band gap energy larger than the well layers of the active layer and the optical guide layer between the light guide layer and the active layer. It is preferable that a cap layer is formed, and the impurity concentration of the cap layer is preferably set to 1 × 10 ¹⁸ / cm ³ or more. As described above, by forming the cap layer having a large band gap energy, a leak current can be reduced. It is more effective if the light guide layer and the cap layer are formed on the p-conductive side nitride semiconductor layer side.

In the present invention, each of the first to third nitride semiconductor elements may be formed by growing a nitride semiconductor layer on a heterogeneous substrate made of a material different from that of the nitride semiconductor. After forming a protective film on the upper surface so as to partially expose the surface of the nitride semiconductor layer, a nitride made of a nitride semiconductor grown to cover the protective film from the exposed nitride semiconductor layer Preferably, it is formed on a semiconductor substrate. Thereby, each layer of the first to third nitride semiconductor elements can be formed with good crystallinity, so that a nitride semiconductor element having excellent characteristics can be formed. In the present invention, the heterogeneous substrate and the protective film may be removed before or after the device growth, leaving the nitride semiconductor layer on which (or to be) formed the nitride semiconductor device as a substrate.

[0038]

FIG. 1 is a schematic sectional view showing the structure of a nitride semiconductor device according to an embodiment of the present invention.
The nitride semiconductor device of this embodiment is a laser device of an electrode stripe type having an end face of an active layer as a resonance surface (henceforth simply referred to as a laser device of the embodiment), and is shown in FIG.
FIG. 3 schematically shows a cross section when the element is cut in a direction perpendicular to the resonance direction of the laser light. Hereinafter, an embodiment of the present invention will be described with reference to FIG.

First, in FIG. 1, each symbol indicates the following. Reference numeral 10 denotes a heterogeneous substrate made of a material different from a nitride semiconductor, such as sapphire, spinel, SiC, Si,
This shows a GaN substrate having a thickness of, for example, 10 μm or more grown on a substrate made of a material such as GaAs or ZnO. The heterogeneous substrate may be removed after forming the GaN substrate 10 as shown in FIG. 1 or may be used without being removed as shown in an embodiment described later (FIG. 4). 11 is Si
4 shows a buffer layer made of doped n-type GaN and an n-side contact layer. Numeral 12 is a position distant from the active layer, for example, a Si-doped n-type Al having a thickness of 40 Å.
The n-side of the superlattice structure in which 100 layers of _0.2 Ga _0.8 N (first nitride semiconductor layer) and 40 Å-thick undoped GaN layers (second nitride semiconductor layer) are alternately stacked. 3 shows a cladding layer. 13 is n
An n-side guide layer made of, for example, undoped GaN is provided between the side cladding layer 12 and the active layer 14 and has a band gap energy smaller than that of Al _0.2 Ga _0.8 N of the n-side cladding layer 12. Reference numeral 14 denotes three well layers of In _0.2 Ga _0.8 N having a thickness of 30 Å, and a film thickness of 30 having a band gap energy larger than that of the well layers.
The active layer has a multiple quantum well structure in which two barrier layers of Angstrom In _0.05 Ga _0.95 N are alternately laminated in total of five layers. 15 is larger than the band gap energy of the well layer of the active layer 14 and
6, greater than the bandgap energy of
4 shows a p-side cap layer made of g-doped p-type Al _0.3 Ga _0.7 N. The band gap energy of the p-side cap layer 15 is preferably a p-side cladding layer 17 having a superlattice structure.
Is larger than the nitride semiconductor layer (fourth nitride semiconductor layer) having the smaller band gap energy. 16
Is between the p-side cladding layer 17 and the active layer 14,
It has a band gap energy smaller than Al _0.2 Ga _0.8 N of the p-side cladding layer 17, for example, undoped G
5 shows a p-side guide layer made of aN. 17 is at a position distant from the active layer, for example, the thickness 40 Å of Mg-doped p-type Al _0.2 Ga _0.8 N and the thickness 40 Å of undoped (undope) GaN layer are 100 are alternately laminated ultra 4 shows a p-side cladding layer having a lattice structure. Reference numeral 18 denotes Al _0.2 Ga _0.8 of the p-side cladding layer 17.
5 shows a p-side contact layer having a band gap energy smaller than N and made of, for example, Mg-doped GaN.

As described above, in the laser device according to the embodiment of the present invention, the above-described nitride semiconductor layers 11 are formed on the GaN substrate 10.
To 18 are stacked, a stripe ridge is formed on the nitride semiconductor layer above the p-side cladding layer 17, and a p-electrode 21 is formed on almost the entire surface of the p-side contact layer 18 on the outermost surface of the ridge. Is formed. On the other hand, an n-electrode 23 is formed on the surface of the n-side buffer layer 11 that is etched and exposed from above the nitride semiconductor layer. In the present embodiment, the n-electrode 23 is formed on the surface of the n-side buffer layer 11. However, since the GaN substrate 10 is used as the substrate, the portion where the n-electrode is formed is etched down to the GaN substrate 10. The surface of the GaN substrate 10 may be exposed, an n-electrode may be formed on the exposed surface of the GaN substrate 10, and a p-electrode and an n-electrode may be provided on the same surface. An insulating film 25 made of, for example, SiO ₂ is provided on the surface of the nitride semiconductor exposed between the n-electrode 23 and the p-electrode 21. A pad electrode 22 and an n-pad electrode 24 are provided. As described above, in this specification, the nitride semiconductor layer between the active layer and the p-electrode, regardless of the conductivity type of the nitride semiconductor layer,
Collectively called p-side nitride semiconductor layer, its active layer and Ga
The nitride semiconductor layers between the N substrate 10 and the N substrate 10 are collectively called an n-side nitride semiconductor layer.

In the laser device according to the embodiment of the present invention, FIG.
In the n-side nitride semiconductor layer below the active layer 14 shown in FIG. 5, a first nitride semiconductor layer having a larger band gap energy and a first nitride semiconductor layer An n-side cladding layer 12 having a superlattice structure in which a second nitride semiconductor layer having a small bandgap energy is laminated and having a different impurity concentration from each other is provided. The first nitride semiconductor layer and the second nitride semiconductor layer forming the superlattice layer have a thickness of 100 Å or less,
The thickness is more preferably adjusted to 70 Å or less, most preferably 10 to 40 Å.
If the thickness is larger than 100 Å, the first nitride semiconductor layer and the second nitride semiconductor layer have a thickness equal to or larger than the limit of elastic strain, and minute cracks or crystal defects tend to be easily formed in the films. In the present invention, the lower limits of the thicknesses of the first nitride semiconductor layer and the second nitride semiconductor layer are not particularly limited, and may be at least one atomic layer.
Most preferably, it is 0 Å or more. Further, the first nitride semiconductor layer is a nitride semiconductor containing at least Al,
Preferably, Al _x Ga ₁ -xN (0 <X ≦ 1) is grown. On the other hand, the second nitride semiconductor may be any nitride semiconductor having a band gap energy smaller than that of the first nitride semiconductor, but is preferably Al _Y Ga _1-Y N (0 ≦ Y < 1, X> Y), In Z Ga 1-Z
Binary mixed crystal and ternary mixed crystal nitride semiconductors such as N (0 ≦ Z <1) can be easily grown, and those having good crystallinity can be easily obtained. Among them, the first nitride semiconductor is particularly preferably Al _x Ga _{1 -x} N containing no In or Ga (0 <X <
1), and the second nitride semiconductor is free of Al an In _Z
Ga ₁ -ZN (0 ≦ Z <1), and in particular, for the purpose of obtaining a superlattice having excellent crystallinity, Al having an Al mixed crystal ratio (Y value) of 0.3 or less.
And _{X Ga 1-X N (0} <X ≦ 0.3), the combination of GaN is most preferable.

Further, a first nitride semiconductor is formed using Al _x Ga ₁ -xN (0 <X <1), and a second nitride semiconductor is formed using GaN.
When the nitride semiconductor of the above is formed, there are excellent manufacturing advantages as described below. That is, in forming the Al _x Ga ₁ -xN (0 <x <1) layer and the GaN layer by the metalorganic gas layer growth method (MOCVD), both layers are the same H _2.
It can be grown in an atmosphere. Therefore, the Al _x Ga ₁ -xN (0 <X <1) layer and the Ga
A superlattice layer can be formed by alternately growing the N layer. This is an extremely great advantage in manufacturing a superlattice layer that needs to be formed by stacking several tens to several hundreds of layers.

When a cladding layer is formed as a light confinement layer and a carrier confinement layer, it is necessary to grow a nitride semiconductor having a larger band gap energy than the well layer of the active layer. The nitride semiconductor layer having a large band gap energy is a nitride semiconductor having a high Al mixed crystal ratio. Conventionally, when a nitride semiconductor having a high Al mixed crystal ratio is grown as a thick film, cracks are easily formed, and crystal growth has been extremely difficult. However, when a superlattice layer is formed as in the present invention, even if the AlGaN layer serving as the first nitride semiconductor layer constituting the superlattice layer is a layer having a somewhat higher Al composition ratio, the AlGaN layer has a thickness less than the elastic critical film thickness. It is hard to crack because it is grown. Therefore, in the present invention, A
Since a layer having a high mixed crystal ratio can be grown with good crystallinity, a cladding layer having a high optical confinement and carrier confinement effect can be formed, and the threshold voltage is reduced in a laser device and Vf (forward voltage) is reduced in an LED device. be able to.

Further, in the laser device according to the embodiment of the present invention, the first nitride semiconductor layer and the second nitride semiconductor layer of the n-side cladding layer 12 have different n-type impurity concentrations. Set. This is so-called modulation doping, in which one layer has a low n-type impurity concentration,
If the other layer is doped at a high concentration, preferably in a state where impurities are not doped (undoped), the threshold voltage, Vf, and the like can be reduced. This is because the presence of a layer with a low impurity concentration in the superlattice layer increases the mobility of that layer, and the presence of a layer with a high impurity concentration at the same time allows the superlattice to remain at a high carrier concentration. This is because a layer can be formed. That is, since a layer having a low impurity concentration and a high mobility and a layer having a high impurity concentration and a high carrier concentration are present at the same time, a layer having a high carrier concentration and a high mobility becomes a cladding layer. , Vf decrease.

When a nitride semiconductor layer having a large band gap energy is doped with an impurity at a high concentration, a two-dimensional electron gas is generated between the high impurity concentration layer and the low impurity concentration layer by the modulation doping. It is presumed that the resistivity decreases due to the influence of the electron gas. For example, in a superlattice layer in which a nitride semiconductor layer with a large band gap doped with an n-type impurity and an undoped nitride semiconductor layer with a small band gap are stacked, a layer doped with an n-type impurity and an undoped layer The barrier layer side is depleted at the interface with the heterojunction, and electrons (two-dimensional electron gas) accumulate at the interface near the thickness on the layer side with a small band gap. Since this two-dimensional electron gas is formed on the side with a smaller band gap, electrons are not scattered by impurities when traveling,
The mobility of electrons in the superlattice increases, and the resistivity decreases.
It is inferred that the p-side modulation dope is also affected by the two-dimensional hole gas. In the case of a p-layer, AlGaN is Ga
The resistivity is higher than that of N. Then p toward AlGaN
It is presumed that the threshold value tends to decrease when the device is manufactured because the resistivity decreases by doping a large amount of the type impurity, and the substantial resistivity of the superlattice layer decreases.

On the other hand, when a nitride semiconductor layer having a small band gap energy is doped with an impurity at a high concentration, the following effects are presumed. For example, AlGaN
Layer and the GaN layer are doped with the same amount of Mg,
In the N layer, the acceptor level of Mg is large and the activation rate is small. On the other hand, the depth of the acceptor level of the GaN layer is shallower than that of the AlGaN layer, and the activation rate of Mg is high. For example, even if Mg is doped at 1 × 10 ²⁰ / cm ^3, GaN
Has a carrier concentration of about 1 × 10 ¹⁸ / cm ³ , whereas AlGaN can only provide a carrier concentration of about 1 × 10 ¹⁷ / cm ³ . Therefore, in the present invention, AlGaN / G
GaN that can form a superlattice with aN and obtain a high carrier concentration
By doping the layer with more impurities, a superlattice with a high carrier concentration can be obtained. Moreover, since the carrier is a superlattice, the carrier moves through the AlGaN layer having a low impurity concentration by the tunnel effect, so that the carrier is not substantially affected by the AlGaN layer, and the AlGaN layer acts as a clad layer having a high band gap energy.
Therefore, even if the nitride semiconductor layer having the smaller band gap energy is heavily doped with impurities, the laser element and the L
This is very effective in lowering the threshold value of the ED element.
In this description, an example is described in which a superlattice is formed on the p-type layer side. However, a similar effect can be obtained when a superlattice is formed on the n-layer side.

When the first nitride semiconductor layer having a large band gap energy is heavily doped with an n-type impurity, a preferable doping amount of the first nitride semiconductor layer is 1
× 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ , more preferably 1 × 10 ²⁰ / cm ³
It is adjusted to a range of × 10 ¹⁸ / cm ^{3 to} 5 × 10 ¹⁹ / cm ³ . 1
If it is less than × 10 ¹⁷ / cm ³ , the difference from the second nitride semiconductor layer will be small, and it tends to be difficult to obtain a layer having a high carrier concentration, and more than 1 × 10 ²⁰ / cm ^3. Then, the leak current of the element itself tends to increase. On the other hand, the n-type impurity concentration of the second nitride semiconductor layer may be lower than that of the first nitride semiconductor layer, preferably 1/10 or more. Most preferably, if undoped, a layer having the highest mobility can be obtained, but since the film thickness is small, n diffused from the first nitride semiconductor side.
There is a type impurity, and its amount is preferably 1 × 10 ¹⁹ / cm ³ or less. As the n-type impurity, an element of Group IVB or VIB of the periodic table such as Si, Ge, Se, S, or O is selected, and preferably, Si, Ge, and S are used as the n-type impurities. This effect is the same when the first nitride semiconductor layer having a large band gap energy is doped with a small amount of n-type impurities and the second nitride semiconductor layer having a small band gap energy is doped with a large amount of n-type impurities. is there.

Further, in the laser device according to the embodiment of the present invention, in the p-side nitride semiconductor layer above the active layer 14 shown in FIG. A p-side cladding having a superlattice structure in which a third nitride semiconductor layer and a fourth nitride semiconductor layer having a smaller bandgap energy than the third nitride semiconductor layer are laminated and have different impurity concentrations from each other. Layer 17
have. Like the n-side cladding layer 12, the third and fourth nitride semiconductor layers constituting the superlattice layer of the p-side cladding layer 17 also have a thickness of 100 angstroms or less, more preferably 70 angstroms or less, and most preferably. The thickness is adjusted to 10 to 40 angstroms. Similarly, the third nitride semiconductor layer is a nitride semiconductor containing at least Al, preferably Al _x Ga ₁ -xN (0 <x ≦ 1).
And the fourth nitride semiconductor is preferably Al _Y Ga _1-Y N (0 ≦ Y <1, X> Y), In _Z G
a _1-Z N 2 mixed crystal such as (0 ≦ Z ≦ 1), it is desirable to grow the nitride semiconductor ternary mixed crystal.

If the p-side cladding layer 17 has a superlattice structure, the effect of the superlattice structure on the laser element is the same as that of the n-side cladding layer 12, but in addition to the case where the p-side cladding layer 17 is formed on the n-layer side. It has the following effects. That is, the p-type nitride semiconductor generally has a resistivity higher by two digits or more than the n-type nitride semiconductor. Therefore, by forming the superlattice layer on the p-layer side, the effect of lowering the threshold voltage appears remarkably. To be more specific, it is known that a nitride semiconductor is a semiconductor from which a p-type crystal is extremely difficult to obtain. A technique for removing hydrogen by annealing a nitride semiconductor layer doped with a p-type impurity to obtain a p-type crystal is known (Japanese Patent No. 2540791). However, even if a p-type is obtained, its resistivity is several Ω · cm or more. Therefore, by using this p-type layer as a superlattice layer, the crystallinity is improved and the resistivity is reduced by one digit or more, so that the threshold voltage can be lowered.

The third nitride semiconductor layer and the fourth nitride semiconductor layer of the p-side cladding layer 17 have different p-type impurity concentrations, and the impurity concentration of one layer is higher and the impurity concentration of the other layer is lower. Make it smaller. Similarly to the n-side cladding layer 12,
If the p-type impurity concentration of the third nitride semiconductor layer having a larger bandgap energy is increased and the fourth p-type impurity concentration having a smaller bandgap energy is reduced, preferably undoped, the threshold voltage, Vf, etc. Can be reduced. The opposite configuration is also possible.
That is, the p-type impurity concentration of the third nitride semiconductor layer having a large band gap energy may be reduced, and the p-type impurity concentration of the fourth nitride semiconductor layer having a small band gap energy may be increased. The reason is as described above.

The preferable doping amount of the third nitride semiconductor layer is 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²¹ / cm ³ , more preferably 1 × 10 ¹⁹ / cm ^{3 to} 5 × 10 ²⁰ / cm. Adjust to the range of ³ . If it is less than 1 × 10 ¹⁸ / cm ³ , the difference from the fourth nitride semiconductor layer is similarly reduced, and it tends to be difficult to obtain a layer having a high carrier concentration.
If it is more than × 10 ²¹ / cm ³ , the crystallinity tends to deteriorate. On the other hand, the p-type impurity concentration of the fourth nitride semiconductor layer may be lower than that of the third nitride semiconductor layer, preferably 1/10 or less. In order to obtain a layer having the highest mobility, undoping is most preferable. Actually, since the film thickness is small, it is considered that there is a p-type impurity diffused from the third nitride semiconductor side. However, in order to obtain a good result in the present invention, the amount is one.
× 10 ²⁰ / cm ³ or less is desirable. The p-type impurities include, for example, Mg, Zn, Ca, Be, etc., from Group IIA of the periodic table and IIB.
A group element is selected, and preferably, Mg, Ca, or the like is used as the p-type impurity. This effect is the same when the third nitride semiconductor layer having a large band gap energy is doped with a small amount of p-type impurities, and the fourth nitride semiconductor layer having a small band gap energy is doped with a large amount of p-type impurities. is there.

Furthermore, in the nitride semiconductor layer constituting the superlattice, the layer in which impurities are doped at a high concentration corresponds to the semiconductor layer central portion (the second nitride semiconductor layer or the fourth nitride semiconductor layer) in the thickness direction. The impurity concentration at a position distant from the nitride semiconductor layer) is high, and the impurity concentration near both ends (portion close to the second nitride semiconductor layer or the fourth nitride semiconductor layer) is low (preferably undoped). It is desirable to do so. More specifically, for example, AlGaN doped with Si as an n-type impurity and undoped G
When a superlattice layer is formed with an aN layer, AlGaN becomes Si
Doping, electrons are emitted to the conduction band as donors, but the electrons fall into the conduction band of GaN having a low potential. Since the GaN crystal is not doped with a donor impurity, carriers are not scattered by the impurity. Therefore, electrons can easily move in the GaN crystal, and the mobility of electrons is substantially increased. This is similar to the effect of the two-dimensional electron gas described above, and the electron mobility in the lateral direction is substantially increased, and the resistivity is reduced. Further, in AlGaN having a large band gap energy, GaN
The effect can be further increased by doping the central region relatively far from the layer with n-type impurities at a high concentration. That is, of the electrons moving in the GaN, the electrons passing through the portion close to the AlGaN layer are somewhat scattered by n-type impurity ions (in this case, Si) in the portion of the AlGaN layer close to the GaN layer. However, as described above, in the AlGaN layer, if a portion near the GaN layer is undoped,
Since electrons passing through a portion close to the AlGaN layer are less likely to be scattered by Si, the mobility of the undoped GaN layer is further improved. Although the function is slightly different, a similar effect is obtained when a superlattice is formed by the third nitride semiconductor layer and the fourth nitride semiconductor layer on the p-layer side, and the third nitride having a large bandgap energy has a similar effect. It is desirable that the central region of the semiconductor layer be heavily doped with a p-type impurity and the portion adjacent to the fourth nitride semiconductor layer be reduced or undoped. On the other hand, a layer in which a nitride semiconductor layer having a small bandgap energy is heavily doped with an n-type impurity may be configured to have the above-described impurity concentration. The effect tends to be small.

While the above description has been given of the case where the n-side cladding layer 12 and the p-side cladding layer 17 are superlattice layers, the present invention also relates to a superlattice layer which is formed of an n-side buffer layer 11, n The side light guide layer 13, the p-side cap layer 15, the p-side light guide layer 16, the p-side contact layer 18, and the like can have a super lattice structure. That is, any layer apart from the active layer, a layer in contact with the active layer, or any other layer can be a superlattice layer. In particular, an n-side buffer layer 1 on which an n-electrode is formed
If 1 is a superlattice, an effect similar to that of the HEMT is likely to appear.

Further, in the laser device according to the embodiment of the present invention, as shown in FIG. 1, an impurity (in this case, an n-type impurity) is provided between the active layer 14 and the n-side cladding layer 12 made of a superlattice layer. An n-side light guide layer 13 having a concentration adjusted to 1 × 10 ¹⁹ / cm ³ or less is formed. Although the n-side light guide layer 13 may be undoped, an n-type impurity may diffuse from another layer and enter. However, in the present invention, the doping amount is 1 × 10 ¹⁹ / cm ³ or less. If it exists, it operates as a light guide layer and does not impair the effects of the present invention. However, in the present invention, the n-side light guide layer 1
The impurity concentration of No. ³ is preferably 1 × 10 ¹⁸ / cm ³ or less, more preferably 1 × 10 ¹⁷ / cm ³ or less, and most preferably undoped. The n-side light guide layer is made of a nitride semiconductor containing In or G
It is desirable to be composed of aN.

In the laser device of the embodiment, the impurity (p-type impurity in this case) concentration is 1 × 10 ¹⁹ / p between the active layer 14 and the p-side cladding layer 17 made of a superlattice layer.
A p-side light guide layer 16 adjusted to cm ³ or less is formed. In the present invention, the impurity concentration of the p-side guide layer 16 may be 1 × 10 ¹⁹ / cm ³ or less, but the preferred impurity concentration is 1 × 10 ¹⁸ / cm ³ or less, and most preferably undoped. In the case of a nitride semiconductor, when it is undoped, it usually shows n-type conductivity. However, in the present invention, the conductivity type of the p-side guide layer 16 may be either n or p. Regardless of this, it is called a p-side light guide layer. Actually, the p-type impurity may diffuse from another layer and enter the p-side light guide layer 16. It is desirable that the p-side light guide layer is also made of a nitride semiconductor containing In or GaN.

The reason why an undoped nitride semiconductor is preferably present between the active layer and the cladding layer is as follows. That is, in the case of a nitride semiconductor, light emission of the active layer is usually 360 to 520 nm, particularly 380 to 450 n.
m. An undoped nitride semiconductor has a lower absorptance of light having the above-mentioned wavelength than a nitride semiconductor doped with an n-type impurity and a p-type impurity. Therefore, an undoped nitride semiconductor, a light emitting active layer,
Since the light emission of the active layer is hardly attenuated by being sandwiched between the cladding layer as the light confinement layer, a laser element oscillating with low gain can be realized, and the threshold voltage can be reduced. Note that this effect can be confirmed when the impurity concentration of the light guide layer is 1 × 10 ¹⁹ / cm ³ or less.

Therefore, as a preferred combination of the present invention, a clad layer having a superlattice structure in which impurities are modulation-doped is provided at a position distant from the active layer, and the impurity concentration is between the clad layer and the active layer. Light-emitting device having a low, preferably undoped guide layer.

As a further preferred embodiment, in the light emitting device of the present invention, the band between the p-side guide layer 16 and the active layer 14 is larger than the band gap energy of the well layer of the active layer and the interface of the p-side guide layer 16. P made of a nitride semiconductor having a gap energy and a thickness of 0.1 μm or less
The side cap layer 15 is formed, and the impurity concentration of the p-side cap layer is adjusted to 1 × 10 ¹⁸ / cm ³ or more. The thickness of the p-type cap layer 15 is 0.1 μm or less,
It is more preferably adjusted to 500 angstrom or less, most preferably 300 angstrom or less. 0.
When grown to a thickness greater than 1 μm, the p-type cap layer 1
This is because cracks are easily formed in the layer 5 and it is difficult to grow a nitride semiconductor layer having good crystallinity. When the layer having a large band gap energy is brought into contact with the active layer in this manner, the layer having a band gap energy of 0.
By forming the thin film having a thickness of 1 μm or less, the leak current of the light emitting element tends to be reduced. As a result, electrons injected from the n-layer side accumulate in the active layer due to the barrier of the energy barrier of the cap layer, and the probability of recombination of electrons and holes increases, thereby improving the output of the device itself. be able to. The impurity concentration is 1 × 10 ¹⁸ / cm ³
It is necessary to adjust above. This cap layer is relatively A
A layer having a high 1-crystal ratio and a layer having a high Al-crystal ratio tend to have high resistance. For this reason, unless the resistivity is lowered by increasing the carrier concentration by doping impurities, this layer becomes like a high-resistance i-layer, and has a pin structure, resulting in poor current-voltage characteristics. This is because it tends to be. The p-side cap layer may be formed on the n-side. When formed on the n-side, n-type impurities may or may not be doped.

In the laser device according to the embodiment configured as described above, the n-side cladding layer 12 and the p-side cladding layer 17 have a superlattice structure. , The threshold voltage can be lowered, and laser oscillation can be performed for a long time. In the laser device of the present embodiment, the n-side cladding layer 12
In addition to the p-side cladding layer 17 having a super lattice structure, various measures are taken as described above to further reduce the threshold voltage.

In the above embodiment, the n-side cladding layer 12
Although the p-side cladding layer 17 has a superlattice structure, the present invention is not limited to this, and one of the n-side cladding layer 12 and the p-side cladding layer 17 may have a superlattice structure. Even in the manner described above, the threshold voltage can be lowered as compared with the conventional example.

In the embodiment, the n-side cladding layer 12
Although the p-side cladding layer 17 has a superlattice structure, the present invention is not limited to this, and any one of the p-side and n-side nitride semiconductor layers other than the n-side cladding layer 12 and the p-side cladding layer 17 may be used. What is necessary is just a superlattice structure. Even with the configuration described above, the threshold voltage can be reduced as compared with the conventional example.

In the above embodiments, the n-side cladding layer 12 and the p-side cladding layer 17 have a superlattice structure in the laser element. However, the present invention is not limited to this, and other nitrides such as a light emitting diode (LED) may be used. It goes without saying that the present invention can be applied to a semiconductor element. By configuring as above,
In a light emitting diode, Vf (forward voltage) can be reduced.

[0063]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 2 is a perspective view showing the shape of the laser device of FIG.

Example 1 A GaN substrate 10 was prepared by growing a single crystal of GaN to a thickness of 50 μm on a substrate of sapphire (C-plane) via a buffer layer of GaN. The GaN substrate 10 was set in a reaction vessel, the temperature was raised to 1050 ° C., hydrogen was used as a carrier gas, ammonia and TMG (trimethylgallium) as source gases, silane gas as an impurity gas, and Si was placed on the GaN substrate 10. An n-side buffer layer 11 of GaN doped with × 10 ¹⁸ / cm ³ is grown to a thickness of 4 μm.
This buffer layer also functions as a contact layer for forming an n-electrode when a light emitting device having a structure as shown in FIG. 1 is manufactured. Further, the n-side buffer layer is a buffer layer grown at a high temperature, for example, sapphire, Si
C, on a substrate made of a material different from the nitride semiconductor such as spinel,
It is distinguished from a buffer layer in which N, AlN or the like is directly grown to a thickness of 0.5 μm or less.

(N-side cladding layer 12 = superlattice layer) Then, at 1050 ° C., TMA (trimethylaluminum),
1 × 1 Si using TMG, ammonia and silane gas
A first layer of 0 ¹⁹ / cm ³ doped n-type Al _0.2 Ga _0.8 N is grown to a thickness of 40 Å, followed by stopping silane gas and TMA, and forming a second layer of undoped GaN to 40 Å. It grows with the film thickness of. A superlattice layer is composed of a first layer + a second layer + a first layer + a second layer +... 100 layers are alternately laminated, each having a total thickness of 0.8 μm. The n-side cladding layer 12 is grown.

(N-side light guide layer 13) Subsequently, the silane gas is stopped and the n-side light guide layer 13 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm. This n-side light guide layer acts as a light guide layer of the active layer,
It is desirable to grow GaN or InGaN, usually 100 Å to 5 μm, more preferably 2 Å.
It is desirable to grow with a film thickness of 00 Å to 1 μm. This layer can also be an undoped superlattice layer. In the case of a superlattice layer, the band gap energy is larger than that of the active layer,
_It should be smaller than _0.2 Ga _0.8 N.

(Active Layer 14) Next, TMG was used as a source gas.
The active layer 14 is grown using TMI and ammonia.
The active layer 14 maintains the temperature at 800 ° C.
A well layer made of n _0.2 Ga _0.8 N is grown to a thickness of 25 Å. Next, a barrier layer made of undoped In _0.01 Ga _0.95 N is grown to a thickness of 50 Å at the same temperature only by changing the molar ratio of TMI. This operation was repeated twice, and finally, a multiple quantum well structure (M
A QW) active layer is grown. The active layer may be undoped as in this embodiment, or may be an n-type impurity and / or a p-type impurity.
Type impurities may be doped. The impurity may be doped into both the well layer and the barrier layer, or may be doped into either one.

(P-side cap layer 15)
Raise to 50 ° C, TMG, TMA, ammonia, Cp2M
g (cyclopentadienyl magnesium), p-type Al _0.3 Ga doped with Mg at 1 × 10 ²⁰ / cm ³ and having a larger band gap energy than the p-side light guide layer 16
_A p-side cap layer 17 of _0.7 N is grown to a thickness of 300 Å. As described above, the p-type cap layer 15 is formed with a winding thickness of 0.1 μm or less, and the lower limit of the film thickness is not particularly limited, but is preferably formed with a film thickness of 10 Å or more.

(P-side light guide layer 16) Subsequently, Cp2M
g, TMA is stopped, and at 1050 ° C., a p-side optical guide layer 16 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 15 is grown to a thickness of 0.1 μm. This layer acts as a light guide layer of the active layer and, like the n-type light guide layer 13, GaN, InGaN
It is desirable to grow with. The p-side optical guide layer may be a superlattice layer made of an undoped nitride semiconductor or an impurity-doped nitride semiconductor. In the case of a superlattice layer, the band gap energy is larger than that of the well layer of the active layer, and Al _0.2 Ga _0.8 of the p-side cladding layer.
Make it smaller than N.

(P-side cladding layer 17)
P-type Al _0.2 Ga doped with Mg at 1 × 10 ²⁰ / cm ³
_A third layer of _0.8 N is grown to a thickness of 40 Å, followed by stopping only TMA and undoping Ga.
A fourth layer of N is grown to a thickness of 40 Å. This operation is repeated 100 times to form a p-side cladding layer 17 composed of a superlattice layer having a total film thickness of 0.8 μm.

(P-side contact layer 18) Finally, 105
At 0 ° C., 2 × 10 ²⁰ Mg was added on the p-side cladding layer 17.
A p-side contact layer 18 made of p-type GaN doped with / cm ³ is grown to a thickness of 150 Å. p
The side contact layer 18 is a p-type In _x Al _Y Ga _{1 -XYN}
(0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably Mg-doped GaN, the p-electrode 21
And the most preferable ohmic contact is obtained. Also p-type A
Because a nitride semiconductor having a small band gap energy is used as a p-side contact layer in contact with the p-side cladding layer 17 having a superlattice structure containing l _Y Ga _1-Y N, the film thickness is reduced to 500 Å or less. In addition, the carrier concentration of the p-side contact layer 18 is substantially increased, a favorable ohmic contact with the p-electrode is obtained, and the threshold current and voltage of the device are reduced.

The wafer on which the nitride semiconductor has been grown as described above is placed in a reaction vessel in a nitrogen atmosphere at 700.degree.
Annealing is performed at a temperature of ° C. to further reduce the resistance of the layer doped with the p-type impurity.

After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 1, the uppermost p-side contact layer 18 and the p-side cladding layer 17 are etched by an RIE apparatus to have a stripe width of 4 μm. Ridge shape. As described above, by forming the layer above the active layer into a stripe-shaped ridge, light emission of the active layer is concentrated below the stripe ridge, and the threshold value is reduced. In particular, the p-side cladding layer 17 composed of a superlattice layer
It is preferable that the above layers have a ridge shape.

Next, a mask is formed on the ridge surface, and RIE is performed.
To expose the surface of the n-side buffer layer 11. The exposed n-side buffer layer 11 also functions as a contact layer for forming the n-electrode 23.
In FIG. 1, the n-side buffer layer 11 is used as a contact layer. However, the GaN substrate 10 can be etched and the exposed GaN substrate 10 can be used as a contact layer.

Next, on the outermost surface of the ridge of the p-side contact layer 18, a p-electrode 21 made of Ni and Au is formed in a stripe shape. Examples of the material of the p-side contact layer and the p-electrode 21 for obtaining a preferable ohmic material include Ni, Pt, and P.
d, Ni / Au, Pt / Au, Pd / Au and the like.

On the other hand, an n-electrode 23 made of Ti and Al is formed in a stripe shape on the surface of the n-side buffer layer 11 that has been exposed earlier. As a material of the n-side buffer layer 11 or the n-electrode 23 that can obtain a preferable ohmic with the GaN substrate 10, a metal or alloy such as Al, Ti, W, Cu, Zn, Sn, and In is preferable.

Next, as shown in FIG.
The surface of the nitride semiconductor layer exposed between the electrode 23 and Si
An insulating film 25 made of O ₂ is formed, and a p pad electrode 22 electrically connected to the p electrode 21 via the insulating film 25 is formed.
And an n-pad electrode 24 are formed. This p pad electrode 2
2 has the effect of increasing the substantial surface area of the p-electrode 21 so that the p-electrode side can be wire-bonded and die-bonded. On the other hand, the n pad electrode 24 is
Has the effect of preventing peeling off.

As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to a polishing apparatus, and the sapphire substrate on which the nitride semiconductor is not formed is wrapped using a diamond polishing agent. Substrate thickness of 70
μm. After wrapping, 1μ with finer abrasive
The substrate surface is mirror-finished by m-polishing, and the entire surface is metallized with Au / Sn.

Then, the Au / Sn side is scribed,
Cleavage is performed in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. SiO ₂ and TiO ₂ on the resonator surface
A dielectric multilayer film was formed, and finally the bar was cut in a direction parallel to the p-electrode to form a laser chip. Next, the chip was placed face-up (in a state where the substrate and the heat sink faced each other), and the electrodes were wire-bonded, and laser oscillation was attempted at room temperature. At room temperature, the threshold current density was 2.0 kA / At cm ² and a threshold voltage of 4.0 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and a lifetime of 1000 hours or more was shown.

[Embodiment 2] FIG. 3 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention. As shown in FIG. The figure at the time of cutting has been shown. Hereinafter, based on this figure, the second embodiment
Will be described. In FIG. 3, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals.

G is placed on a substrate made of sapphire (C-plane).
5 × 10 ¹⁸ / cm 3 through a buffer layer made of aN
A GaN substrate 10 is prepared by growing a single crystal of ^3- doped GaN with a thickness of 150 μm. An n-side buffer layer 1 is formed on the GaN substrate 10 in the same manner as in the first embodiment.
Grow one.

(Crack prevention layer 19) n-side buffer layer 1
1 After the growth, the temperature was raised to 800 ° C.
Using silane gas for TMI, ammonia and impurity gas,
A crack preventing layer 19 made of In _0.1 Ga _0.9 N doped with 5 × 10 ¹⁸ / cm ^{3 of} Si is grown to a thickness of 500 Å. The crack prevention layer 19 is made of an n-type nitride semiconductor containing In, preferably InGaN, so that cracks can be prevented from entering the nitride semiconductor layer containing Al. The crack preventing layer is preferably grown to a thickness of 100 Å or more and 0.5 μm or less. When the thickness is less than 100 Å, it is difficult to function as a crack prevention as described above. When the thickness is more than 0.5 μm, the crystal itself tends to turn black.

After the growth of the crack preventing layer 19, the n-side cladding layer 12 made of a modulation-doped superlattice and the undoped n-side light guide layer 13 are grown in the same manner as in the first embodiment.

(N-side cap layer 20) Subsequently, TMG, T
The n-side cap layer 20 made of n-type Al _0.3 Ga _0.7 N doped with Si at 5 × 10 ¹⁸ / cm ³ and having a band gap energy larger than that of the n-side light guide layer 13 using MA, ammonia, and silane gas is 300 Å. It grows with the film thickness of.

Thereafter, the active layer 14, p
Side cap layer 15, undoped p-side light guide layer 16, p-side cladding layer 17 composed of modulation-doped superlattice, p
The side contact layer 18 is grown.

After growing the nitride semiconductor layer, annealing is performed in the same manner to further reduce the resistance of the p-type impurity-doped layer. After annealing, as shown in FIG. The p-side cladding layer 17 is etched into a ridge shape having a stripe width of 4 μm.

After the formation of the ridge, a p-electrode 21 made of Ni / Au is formed in a stripe shape on the outermost surface of the ridge of the p-side contact layer 18, and the outermost nitride semiconductor layer other than the p-electrode 21 is made of SiO _2. An insulating film 25 is formed, and a p pad electrode 22 electrically connected to the p electrode 21 via the insulating film 25 is formed.

As described above, the wafer on which the p-electrode is formed is transferred to the polishing apparatus, the sapphire substrate is removed by polishing, and the surface of the GaN substrate 10 is exposed. An n-electrode 23 made of Ti / Al is formed on almost the entire exposed GaN substrate surface.

After the electrodes are formed, the GaN substrate is cleaved on the M plane (a plane corresponding to the side surface of a hexagonal prism when the nitride semiconductor is approximated by a hexagonal system), and the cleavage plane is formed of a dielectric material composed of SiO ₂ and TiO _2. A multilayer film is formed, and finally, in a direction parallel to the p-electrode,
The bar is cut to form a laser element. This laser device also exhibited continuous oscillation at room temperature, and exhibited substantially the same characteristics as those of Example 1.

Example 3 In Example 1, after growing the n-side buffer layer 11, a crack preventing layer 19 is grown in the same manner as in Example 2. Next, on the crack prevention layer,
An n-side cladding layer 12 consisting of a single layer of Al _0.3 Ga _0.7 N doped with 1 × 10 ¹⁹ / cm ^{3 of} Si is grown to a thickness of 0.4 μm. After that, when a laser device was manufactured in the same manner as in Example 1, laser oscillation was also exhibited at room temperature, but the life was slightly shorter than that of the laser device of Example 1.

Example 4 In Example 1, when growing the p-side cladding layer 17, a single layer of Al _0.3 Ga _0.7 N doped with Mg at 1 × 10 ²⁰ / cm ³ was grown to a thickness of 0.4 μm. Other than that, when a laser device was manufactured in the same manner as in Example 1, the laser oscillation was also exhibited at room temperature, but the life was slightly shorter than that of the laser device of Example 1.

Fifth Embodiment In the first embodiment, the n-side cladding layer 12 is not made to have a superlattice structure, but Si is 1 × 10 ¹⁸ / cm 2.
An Al _0.2 Ga _0.8 N layer doped with cm ^{3 is} 0.4 μm.
Similarly, the p-side cladding layer does not have a superlattice structure.
Al _0.2 Ga _0.8 N layer doped with 1 × 10 ²⁰ / cm ³ .
4 μm. Instead, the n-side light guide layer 13 is made of undoped In _0.01 Ga _0.99 N layer 30 Å and S
i has a superlattice structure having a total thickness of 0.12 μm in which a GaN layer 30 Å doped with 1 × 10 ¹⁷ / cm ³ is laminated, and the p-side light guide layer 16 is undoped In _0.01 Ga
_0.99 N layer 30 Å and Mg 1 × 10 ¹⁷ /
A laser device was fabricated in the same manner as in Example 1 except that a superlattice structure having a total film thickness of 0.12 μm was formed by laminating a GaN layer 30 Å doped with cm ^3. Laser oscillation was also exhibited at room temperature. The service life was slightly shorter than that of the laser device of Example 1.

Example 6 In Example 1, when forming the n-side buffer layer 11, 30 Å of the undoped GaN layer and 30 of the Al _0.05 Ga _0.95 N layer doped with 1 × 10 ¹⁹ / cm ^{3 of} Si were used. A superlattice layer having a total film thickness of 1.2 μm is formed by stacking Angstrom. After that, Example 1
In the same manner as described above, a layer above the n-side cladding layer 12 is grown to obtain a laser device. However, when forming the n-electrode, the surface to be exposed by etching is set at the middle of the above-described 1.2 μm superlattice layer, and the n-electrode is formed on the superlattice layer. This laser element also oscillates continuously at room temperature, the threshold value is slightly lower than that of the first embodiment, and the lifetime is 1000
It was more than an hour.

[Embodiment 7] FIG. 4 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention, and the same reference numerals as those in the other drawings denote the same layers. Hereinafter, a seventh embodiment will be described with reference to FIG.

As in Example 1, 2 inches φ, (000
1) 500 on the sapphire substrate 30 having the C plane as a main surface
At ℃, a GaN buffer layer (not shown)
After growing to a thickness of 0 Å, the temperature was increased to 10 Å.
At 50 ° C., an undoped GaN layer 31 is grown to a thickness of 5 μm. Note that the film thickness to be grown is not limited to 5 μm, and it is desirable to grow the film to a thickness larger than that of the buffer layer and to adjust the film thickness to 10 μm or less.
The substrate is sapphire, SiC, ZnO, spinel, G
A substrate made of a material different from a nitride semiconductor, which is known for growing a nitride semiconductor such as aAs, can be used.

Next, after growing the undoped GaN layer 31,
The wafer is taken out of the reaction vessel, a striped photomask is formed on the surface of the GaN layer 31, and the CVD is performed.
The protective film 32 made of SiO _{2 having a} stripe width of 20 μm and a stripe interval (window portion) of 5 μm is formed by using an apparatus.
It is formed with a film thickness of. FIG. 4 is a schematic cross-sectional view showing a partial wafer structure when cut in a direction perpendicular to the major axis direction of the stripe. The shape of the protective film is striped,
Any shape such as a dot shape or a grid shape may be used. It is easy to grow the GaN substrate 10 with less noise. As a material of the protective film, for example, silicon oxide (SiO 2)
_X ), silicon nitride (Si _X N _Y ), titanium oxide (Ti
O _X), an oxide such as zirconium oxide (ZrO _X), nitrides, or other of these multilayer films, it is possible to use a metal or the like having a 1200 ° C. or more melting point. These protective film materials have the property of withstanding the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C. and preventing the nitride semiconductor from growing or hardly growing on the surface thereof.

After the formation of the protective film 32, the wafer is set in the reactor again, and a GaN layer serving as the GaN substrate 10 made of undoped GaN is grown at 1050 ° C. to a thickness of 10 μm. The preferred growth thickness of the GaN layer to be grown varies depending on the thickness and size of the protective film 32 formed earlier, but the lateral direction (perpendicular to the thickness direction) above the protective film covers the surface of the protective film 32. ) In a sufficient thickness so as to grow in the same direction. As described above, when the GaN substrate 10 is grown on the surface of the protective film 32 having a property in which the nitride semiconductor is unlikely to grow by a method of growing the GaN layer in the lateral direction, the GaN layer is initially formed on the protective film 32. Does not grow, and a GaN layer is selectively grown on the undoped GaN layer 31 in the window. Subsequently, when the growth of the GaN layer is continued, G
The aN layer grows in the lateral direction, covers and overlies the protective film 32, and the GaN layers grown from adjacent windows are connected to each other, as if a GaN layer had grown on the protective film 32. Becomes That is, the protective film 32 is formed on the GaN layer 31.
To grow a GaN layer in the lateral direction. Here, what is important is that the G grown on the sapphire substrate 30 is
The number of crystal defects in the aN layer 31 and the number of crystal defects in the GaN substrate 10 grown on the protective film 32. That is, due to the mismatch of the lattice constant between the heterogeneous substrate and the nitride semiconductor, a large number of crystal defects are generated in the nitride semiconductor grown on the heterogeneous substrate, and the crystal defects are sequentially formed in the upper layer. During the growth of the semiconductor, it propagates to the surface.
On the other hand, as in the seventh embodiment, the GaN substrate 10 laterally grown on the protective film 32 is not directly grown on a heterogeneous substrate, but is a GaN layer grown from an adjacent window.
Since the crystal defects are connected during the growth by growing laterally on the protective film 32, the number of crystal defects is much smaller than that of the crystal grown directly from a heterogeneous substrate. Therefore,
This is implemented by forming a partially formed protective film on a nitride semiconductor layer grown on a heterogeneous substrate and using a GaN layer grown laterally on the protective film as a substrate. As compared with the GaN substrate of Example 1, a GaN substrate having much less crystal defects can be obtained. Actually, the crystal defect of the undoped GaN layer 31 is 10 ¹⁰ / cm ² or more, but the crystal defect of the GaN substrate 10 according to the method of Embodiment 7 is 10 ⁶ / cm ^2.
It can be reduced to:

After the GaN substrate 10 is formed as described above, Si is deposited on the GaN substrate 10 in the same manner as in the first embodiment.
After growing an n-side buffer layer made of GaN doped with × 10 ¹⁸ / cm ³ and the contact layer 11 with a thickness of 5 μm, Si was doped at 5 × 10 ¹⁸ / cm ³ in the same manner as in Example 2. Crack preventing layer 19 made of In _0.1 Ga _0.9 N
Is grown to a thickness of 500 angstroms. Incidentally, the crack prevention layer 19 may be omitted.

(The central part has a high impurity concentration of a superlattice structure of n.
Side clad layer 12) Next, a second nitride semiconductor layer having a small band gap energy is formed at 1050 ° C. by growing an undoped GaN layer to a thickness of 20 Å using TMG and ammonia gas. Next, at the same temperature, TMA was added and undoped Al
_{A 0.1} Ga _0.9 N layer is grown for 5 Å, and then a silane gas is added to grow an Al _0.1 Ga _0.9 N layer doped with 1 × 10 ¹⁹ / cm ^{3 of} Si to a thickness of 20 Å. Undoped Al _0.1 Ga _0.9 N
The layer is further grown to a thickness of 5 angstroms to achieve a high bandgap energy thickness of 30 μm.
m first nitride semiconductor layers are formed. Thereafter, similarly, the second nitride semiconductor layer and the first nitride semiconductor layer are formed alternately and repeatedly. In Example 7, the second nitride semiconductor layer and the first nitride semiconductor layer
The n-side cladding layer 12 having a superlattice structure and having a thickness of 0.6 μm is formed by laminating so as to have zero layers.

Next, as in the first embodiment, an n-side light guide layer 13, an active layer 14, a p-side cap layer 15, and a p-side light guide layer 16 are sequentially grown.

(P center of superlattice structure with high impurity concentration
Side cladding layer 17) Next, a fourth nitride semiconductor layer having a small band gap energy is formed by growing an undoped GaN layer to a thickness of 20 angstroms at 1050 ° C. using TMG and ammonia gas. Next, at the same temperature, TMA was added and undoped Al
_{A 0.1} Ga _0.9 N layer is grown for 5 Å, and then Cp ₂ Mg is added and Mg is doped at 1 × 10 ²⁰ / cm ^3.
After growing a _0.1 Ga _0.9 N layer to a thickness of 20 angstroms, Cp ₂ Mg is stopped and undoped Al _0.1 Ga
_A third nitride semiconductor layer having a large band gap energy and a thickness of 30 μm is formed by further growing the _0.9 N layer to a thickness of 5 Å. Thereafter, similarly, a fourth nitride semiconductor layer and a third nitride semiconductor layer are alternately and repeatedly formed. In the seventh embodiment, the fourth
And a third nitride semiconductor layer are laminated so as to have 120 layers each, to form a 0.6 μm thick n-side cladding layer 17 having a superlattice structure.

Finally, after growing the p-side contact layer 18 in the same manner as in Example 1, the wafer is taken out of the reaction vessel, annealed, and then etched to remove the p-side cladding layer 17 or more. The shape is a stripe-shaped ridge.

Next, as shown in FIG. 4, the ridge is etched symmetrically to form an n-electrode 23.
The n-electrode 23 is formed by exposing the surface of the side buffer layer, while the p-electrode 21
Are formed in a stripe shape. After that, when a laser device was fabricated in the same manner as in Example 1, the threshold, current density, and voltage were reduced by about 10% as compared with those of Example 1,
The continuous oscillation lifetime at a wavelength of 405 nm showed a lifetime of 2000 hours or more. This is largely due to the use of the GaN substrate 10 having a small number of crystal defects and the improvement of the crystallinity of the nitride semiconductor. In FIG. 4, Ga
When the N substrate 10 is grown to a thickness of, for example, 80 μm or more, the different substrate 30 to the protective film 32 can be removed.

[Embodiment 8] In Embodiment 7, when growing the n-side cladding layer 12, the central portion is not made to have a high impurity concentration, the normal undoped GaN layer is 20 Å, and Si is 1 × 10 ¹⁹ / cm 2. ³ doped Al _0.1 Ga _0.9
The N layer is laminated with 20 Å, and the total film thickness is 0.6
It has a superlattice structure of μm.

On the other hand, when the p-side cladding layer 17 is grown, the undoped GaN
The layer is 20 Å and the Mg is 1 × 10 ²⁰ / cm ³
A laser device was fabricated in the same manner as in Example 7, except that a doped Al _0.1 Ga _0.9 N layer was laminated with 20 Å to form a superlattice structure having a _total film thickness of 0.6 μm. In comparison, although the threshold value was slightly lowered, the life was almost the same at 2000 hours or more.

Example 9 In Example 7, when growing the n-side cladding layer 12, 25 Å of a GaN layer doped with 1 × 10 ¹⁹ / cm ^{3 of} Si and 25 of an undoped Al _0.1 Ga _0.9 N layer were used. And Angstrom are alternately laminated to form a superlattice structure having a total film thickness of 0.6 μm. On the other hand, when growing the p-side cladding layer 17, Mg
Same as Example 7 except that 25 Å of a GaN layer doped with 10 ²⁰ / cm ³ and 25 Å of an undoped Al _0.1 Ga _0.9 N layer are alternately laminated to form a superlattice structure having a _total thickness of 0.6 μm. As a result, a laser element having substantially the same characteristics and life as those of Example 7 was obtained.

Example 10 In Example 7, when growing the n-side cladding layer 12, Si was added to 1 × 10 ¹⁹ / cm ^3.
The doped GaN layer is 25 Å, and the Si _0.1 × 10 ¹⁷ / cm ³ -doped Al _0.1 Ga _0.9 N layer is 25 Å.
Angstrom and alternately, total thickness 0.6μm
Superlattice structure. On the other hand, when growing the p-side cladding layer 17, GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is also used.
25 Å layer and 1 × 10 ¹⁸ / cm ³ Mg
A laser device was fabricated in the same manner as in Example 7 except that a doped Al _0.1 Ga _0.9 N layer was alternately laminated at 25 Å to form a superlattice structure having a _total film thickness of 0.6 μm. A laser device having characteristics and a life almost equivalent to those of the device was obtained.

[Embodiment 11] In the seventh embodiment, the n-side cladding layer was not made to have a superlattice structure, and Si was set to 1 × 10 ¹⁹ / cm.
^{A 3-} doped Al _0.1 Ga _0.9 N layer is grown to a thickness of 0.6 μm. On the other hand, when growing the p-side cladding layer 17, the GaN layer doped with Mg at 1 × 10 ²⁰ / cm ³
Angstroms and 1 × 10 ¹⁸ / cm ³ doped Al
Example 7 except that a _0.1 Ga _0.9 N layer was alternately laminated with 25 Å to form a superlattice structure having a _total film thickness of 0.6 μm.
When a laser device was manufactured in the same manner as in Example 7, the threshold value was slightly increased as compared with Example 7, but the life was also 1000 hours or more.

[Embodiment 12] In Embodiment 7, the impurity concentration in the superlattice of the n-side cladding layer and the p-side cladding layer is set to normal modulation doping (the central part is not high, but is substantially uniform in the layer). When growing the n-side buffer layer 11, Al _0.05 Ga doped with 1 × 10 ¹⁹ / cm ^{3 of} Si is used.
_{A 0.95} N layer and 50 Å of an undoped GaN layer are alternately grown to a total film thickness of 2 μm.
A laser device was fabricated in the same manner as in Example 7, except that the superlattice layer was made m. As compared with the laser device of Example 7, the threshold value was slightly lowered, and the life was 3,000 hours or more.

Example 13 In Example 7, the n-side cladding layer 12 was made of undoped GaN layer 20 Å, and Al _0.1 Ga doped with 1 × 10 ¹⁹ / cm ^{3 of} Si.
A total film thickness of _0.9 N layer and 20 angstroms is laminated.
A 6 μm superlattice structure is used. The next n-side light guide layer 13 is formed by alternately growing 25 Å of a GaN layer doped with 1 × 10 ¹⁹ / cm ³ of Si and 25 Å of an undoped Al _0.05 Ga _0.95 N layer to a total thickness of 0.1 μm.
Superlattice structure.

On the other hand, the p-side light guide layer also contains Mg of 1 × 10
^A 25 Å layer of ¹⁹ / cm ³ doped GaN;
Undoped Al _0.05 Ga _0.95 N layers and 25 Å are alternately grown to form a superlattice structure with a total thickness of 0.1 μm. Next, an undoped GaN layer of 20 Å of the p-side cladding layer 17 and 20 Å of an Al _0.1 Ga _0.9 N layer doped with 1 × 10 ²⁰ / cm ^{3 of} Mg were alternately laminated, and a _total film thickness of 0.6 μm was formed. A laser device was manufactured in the same manner except that the laser device had a superlattice structure.
It showed 0 hours or more.

[Embodiment 14] Embodiment 14 is a laser device constructed using a GaN substrate 10 as in Embodiment 7. That is, the laser device of Example 14 is configured by forming the following semiconductor layers on the GaN substrate 10 configured in the same manner as Example 7. First, n-type Ga doped with 1 × 10 ¹⁸ / cm ³ or more on the GaN substrate 10 is used.
An n-side contact layer made of N (n-side second nitride semiconductor layer) is grown to a thickness of 2 μm. Note that the this layer of undoped GaN, doped with Si Al _X Ga _1-X N
A superlattice layer made of (0 <X ≦ 0.4) may be used.

Next, after growing the n-side contact layer,
The temperature was set to 800 ° C., and in a nitrogen atmosphere, TMG, TM
I, ammonia, silane gas, Si is 5 × 10 ¹⁸ / c
m ³ doped crack preventing layer In consisting _0.1 Ga _0.9 N and the is grown to the thickness of 500 angstroms. By growing this crack prevention layer with an n-type nitride semiconductor containing In, preferably InGaN, cracks can be prevented from entering the nitride semiconductor layer containing Al to be grown later. This crack prevention layer is 10
It is preferable to grow the film with a thickness of 0 Å to 0.5 μm. If it is thinner than 100 Å, it is difficult to act as a crack prevention as described above,
If it is thicker than 0.5 μm, the crystals themselves tend to turn black.

Subsequently, at 1050 ° C., TMA, TMG, ammonia, and silane gas were used to convert Si into 1 × 10 ¹⁹ / cm 3.
^{A layer made of 3-} doped n-type Al _0.2 Ga _0.8 N is grown to a thickness of 40 Å, and an undoped GaN layer is grown to a thickness of 40 Å. An n-side cladding layer composed of a 0.8 μm superlattice is grown.

Subsequently, an n-side optical guide layer made of undoped Al _0.05 Ga _0.95 N is grown to a thickness of 0.1 μm. This layer functions as a light guide layer for guiding light of the active layer, and may be doped with an n-type impurity in addition to undoping. This layer may be a superlattice layer made of GaN and AlGaN.

Next, an active layer made of undoped In _0.01 Ga _0.99 N is grown to a thickness of 400 Å.

Next, Mg having a bandcap energy higher than that of a p-side light guide layer to be formed later is added to 1 × 10 ¹⁹ / Mg.
A p-side cap layer made of p-type Al _0.2 Ga _0.8 N doped with cm ³ is grown to a thickness of 300 Å.

Next, p of Al _0.01 Ga _0.99 N whose band cap energy is smaller than that of the p-side cap layer.
The side light guide layer is grown to a thickness of 0.1 μm. This layer acts as a light guide layer for the active layer. Note that this p
The side light guide layer may be a superlattice layer made of an undoped nitride semiconductor. When a superlattice layer is used, the bandcap energy of a layer (barrier layer) having a larger bandcap energy is larger than that of the active layer and smaller than that of the p-side cladding layer.

Subsequently, a p-type Al _0.2 Ga _0.8 N layer doped with Mg at 1 × 10 ¹⁹ / cm ³ was set to 40 Å,
A p-layer having a superlattice layer structure having a total film thickness of 0.8 μm, in which undoped GaN is alternately stacked with 40 angstroms.
Grow the side cladding layer.

Finally, on the p-side cladding layer, Mg was
A p-side contact layer made of p-type GaN doped with × 10 ²⁰ / cm ³ is grown to a thickness of 150 Å. In particular, in the case of a laser device, a nitride semiconductor having a small bandgap energy is used as a p-side contact layer in contact with a p-side cladding layer having a superlattice structure containing AlGaN, and its thickness is reduced to 500 angstroms or less. Substantially, the carrier concentration of the p-side contact layer is increased, a favorable ohmic contact with the p-electrode is obtained, and the threshold current and voltage of the device tend to decrease.

After the wafer on which the nitride semiconductor has been grown as described above is annealed at a predetermined temperature to further reduce the resistance of the layer doped with the p-type impurity, the wafer is taken out of the reaction vessel and subjected to RIE. Top layer p
The side contact layer and the p-side cladding layer are etched to form a ridge shape having a stripe width of 4 μm.
As described above, by forming the layer above the active layer into a stripe-shaped ridge shape, light emission of the active layer is concentrated below the stripe ridge, and the threshold value is reduced.
In particular, it is preferable that a layer above the p-side cladding layer composed of a superlattice layer has a ridge shape.

Next, a mask is formed on the ridge surface, and RIE is performed.
To expose the surface of the n-side contact layer, and form an n-electrode made of Ti and Al in a stripe shape. On the other hand, on the outermost surface of the ridge of the p-side contact layer, a p-electrode made of Ni and Au is formed in a stripe shape. p-type G
Examples of the electrode material that can obtain a preferable ohmic with the aN layer include Ni, Pt, Pd, Ni / Au, and Pt / A.
u, Pd / Au and the like. Examples of electrode materials that can obtain a preferable ohmic with n-type GaN include Al,
Examples include metals or alloys such as Ti, W, Cu, Zn, Sn, and In.

Next, an insulating film made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode and the n-electrode, and the p-electrode electrically connected to the p-electrode via this insulating film. A pad electrode is formed. This p-pad electrode enlarges the substantial surface area of the p-electrode so that the p-electrode side can be wire-bonded and die-bonded.

As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to a polishing apparatus, and the sapphire substrate on which the nitride semiconductor is not formed is wrapped using a diamond polishing agent. Substrate thickness of 70
μm. After wrapping, 1μ with finer abrasive
The substrate surface is mirror-finished by m-polishing, and the entire surface is metallized with Au / Sn.

Then, the Au / Sn side is scribed,
Cleavage is performed in a bar shape in the direction perpendicular to the stripe-shaped electrode, and a resonator is formed on the cleavage surface. SiO ₂ and TiO ₂ are formed on the resonator surface.
Finally, a bar is cut in a direction parallel to the p-electrode to form a laser chip. Next, the chip was placed face-up (in a state where the substrate and the heat sink faced each other), and the electrodes were wire-bonded and laser oscillation was attempted at room temperature. At room temperature, the threshold current density was 2.0 kA / cm ² ,
At a threshold voltage of 4.0 V, continuous oscillation with an oscillation wavelength of 368 nm was confirmed, and a lifetime of 1000 hours or more was shown.

[0126]

As described above, in the present invention, a laser device capable of continuous oscillation for a long time with a reduced threshold voltage because of having a clad layer composed of a superlattice layer in which impurities are modulation-doped is provided. Can be realized. Further, this laser device can realize a good laser device having a high characteristic temperature. Characteristic temperature is the threshold current density due to temperature change exp
{T: operating temperature (K), T ₀ : characteristic temperature (K)} proportional to (T / T ₀ ). The larger T ₀ indicates that the LD operates stably with a lower threshold current density even at high temperatures. For example, in the laser device according to the first embodiment of the present invention, T ₀ is 150
K or more. This value indicates that the temperature characteristics of the LD are very excellent. For this reason, by using the laser element of the present invention as a writing light source and a reading light source, an unprecedented capacity can be achieved, and its industrial utility value is very large.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a laser device according to one embodiment of the present invention.

FIG. 2 is a perspective view of the laser device of FIG.

FIG. 3 is a schematic sectional view showing the structure of a laser device according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view showing the structure of a laser device according to Example 7 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... GaN substrate, 11 ... n side buffer layer, 12 ... n side clad layer of super lattice structure, 13 ... n side guide layer, 14 ... active layer, 15 ... p Side cap layer, 16 ... p-side guide layer, 17 ... p-side cladding layer of super lattice structure, 18 ... p-side contact layer, 19 ... crack prevention layer, 20 ... n-side cap Layers 21 ... p electrode 22 ... p pad electrode 23 ... n electrode 24 ... n pad electrode 25 ... insulating film.

Claims (44)

[Claims] 1. A nitride semiconductor device comprising an active layer formed between an n-conductive side nitride semiconductor layer and a p-conductive side nitride semiconductor layer, wherein the n-conductive side nitride semiconductor is provided. In the layer, n and n are formed by stacking first and second nitride semiconductor layers having different band gap energies and different n-type impurity concentrations from each other at a position separated from or in contact with the active layer.
A nitride semiconductor device having a side strain superlattice layer. 2. A nitride semiconductor device wherein an active layer is formed between a nitride semiconductor layer on an n-conductive side and a nitride semiconductor layer on a p-conductive side, wherein the nitride semiconductor on the p-conductive side is provided. In a layer, p and n are formed by stacking third and fourth nitride semiconductor layers having different band gap energies and different p-type impurity concentrations from each other at a position separated from or in contact with the active layer.
A nitride semiconductor device having a side strain superlattice layer. 3. A nitride semiconductor device comprising an active layer formed between an n-conductive side nitride semiconductor layer and a p-conductive side nitride semiconductor layer, wherein the n-conductive side nitride semiconductor is provided. In the layer, n and n are formed by stacking first and second nitride semiconductor layers having different band gap energies and different n-type impurity concentrations from each other at a position separated from or in contact with the active layer.
A third strained superlattice layer, wherein the p-type nitride semiconductor layer has a band gap energy different from each other and a p-type impurity concentration different from each other at a position apart from or in contact with the active layer; And a fourth nitride semiconductor layer
A nitride semiconductor device having a side strain superlattice layer. 4. In the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and an n-type larger than the second nitride semiconductor layer. 4. The nitride semiconductor device according to claim 1, which has an impurity concentration. 5. In the first nitride semiconductor layer, an n-type impurity concentration in a portion close to the second nitride semiconductor layer is lower than that in a portion remote from the second nitride semiconductor layer. The nitride semiconductor device according to claim 4, wherein 6. An n-type impurity concentration of the first nitride semiconductor layer is in a range of 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ³ , and an n-type impurity of the second nitride semiconductor layer is Concentration is 1 × 10
6. The nitride semiconductor device according to claim 4, wherein the nitride semiconductor device has a density of ¹⁹ / cm ³ or less. 7. In the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and an n-type smaller than the second nitride semiconductor layer. 4. The nitride semiconductor device according to claim 1, which has an impurity concentration. 8. In the second nitride semiconductor layer, an n-type impurity concentration in a portion close to the first nitride semiconductor layer is lower than that in a portion far from the first nitride semiconductor layer. The nitride semiconductor device according to claim 7, wherein 9. The n-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³ or less, and the n-type impurity concentration of the second nitride semiconductor layer is 1 × 10 ¹⁷ / cm 3. ³ to 1 × 1
9. The nitride semiconductor device according to claim 7, wherein the range is 0 ²⁰ / cm ³ . 10. The first nitride semiconductor layer is formed of Al _Y G
5. The semiconductor device according to claim 4, wherein a _1-Y N (0 <Y <1) is used, and said second nitride semiconductor layer is made of In _x Ga _1-x N (0 ≦ X <1).
10. The nitride semiconductor device according to any one of to 9 above. 11. The nitride semiconductor device according to claim 10, wherein said second nitride semiconductor layer is made of GaN. 12. The first nitride semiconductor layer is made of Al _X G
10. The semiconductor device according to claim 4, wherein a _1-X N (0 <X <1) is used, and said second nitride semiconductor layer is made of Al _Y Ga _1-Y N (0 <Y <1, X> Y). The nitride semiconductor device according to one of the above. 13. The nitride according to claim 4, wherein the first nitride semiconductor layer or the second nitride semiconductor layer is not doped with an n-type impurity. Semiconductor element. 14. The p-side strained superlattice layer, wherein the third nitride semiconductor layer has a band gap energy larger than that of the fourth nitride semiconductor layer and a p-type larger than that of the fourth nitride semiconductor layer. 3. The semiconductor device according to claim 2, which has an impurity concentration.
Or the nitride semiconductor device according to 3. 15. In the third nitride semiconductor layer,
15. The nitride semiconductor device according to claim 14, wherein a p-type impurity concentration in a portion close to the fourth nitride semiconductor layer is lower than that in a portion far from the fourth nitride semiconductor layer. 16. The p-type impurity concentration of the third nitride semiconductor layer is in the range of 1 × 10 ¹⁸ / cm ³ to 1 × 10 ²¹ / cm ³ , and the p-type impurity of the fourth nitride semiconductor layer is Concentration is 1 × 10
13. The nitride semiconductor device according to claim 11, wherein the nitride semiconductor device has a density of ²⁰ / cm ³ or less. 17. In the p-side strained superlattice layer, the third nitride semiconductor layer has a bandgap energy larger than that of the fourth nitride semiconductor layer and a p-type smaller than that of the fourth nitride semiconductor layer. 3. The semiconductor device according to claim 2, wherein
Or the nitride semiconductor device according to 3. 18. In the fourth nitride semiconductor layer,
18. The nitride semiconductor device according to claim 17, wherein a p-type impurity concentration in a portion close to the third nitride semiconductor layer is lower than that in a portion far from the third nitride semiconductor layer. 19. The p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ²⁰ / cm ³ or less, and the p-type impurity concentration of the fourth nitride semiconductor layer is 1 × 10 ¹⁸ / cm ^3. ~ 1 × 10
19. The nitride semiconductor device according to claim 17, wherein the range is ²¹ / cm ³ . 20. The third nitride semiconductor layer is formed of Al _Y G
_{a 1-Y N (0 <} Y <1) consists, said fourth semiconductor layer is _{In X Ga 1-X N (} 0 ≦ X <1) consists of claim 1
20. The nitride semiconductor device according to one of 4 to 19. 21. The nitride semiconductor device according to claim 20, wherein said fourth nitride semiconductor layer is made of GaN. 22. The third nitride semiconductor layer is made of Al _X G
20. The semiconductor device according to claim 14, wherein a _1-X N (0 <X <1) is used, and wherein the fourth nitride semiconductor layer is made of Al _Y Ga _1-Y N (0 <Y <1, X> Y). The nitride semiconductor device according to one of the above. 23. The nitride according to claim 14, wherein the third nitride semiconductor layer or the fourth nitride semiconductor layer is not doped with a p-type impurity. Semiconductor element. 24. In the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than the second nitride semiconductor layer and an n-type larger than the second nitride semiconductor layer. An impurity concentration, and in the p-side strained superlattice layer, the third nitride semiconductor layer has a bandgap energy larger than that of the fourth nitride semiconductor layer and a bandgap energy higher than that of the fourth nitride semiconductor layer. 4. The nitride semiconductor device according to claim 3, having a high p-type impurity concentration. 25. An n-type impurity concentration of the second nitride semiconductor layer, wherein an n-type impurity concentration of the first nitride semiconductor layer is in a range of 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ^3. 1 × 1 impurity concentration
0 ¹⁹ / cm ³ or less, and the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 3
¹⁸ / cm ³ to 1 in the range of × 10 ²¹ / cm ^3, said fourth semiconductor according to claim 24, wherein the p-type impurity concentration of the nitride semiconductor layer is 1 × 10 ²⁰ / cm ³ or less element. 26. In the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and an n-type larger than the second nitride semiconductor layer. An impurity concentration, and in the p-side strained superlattice layer, the third nitride semiconductor layer has a bandgap energy larger than that of the fourth nitride semiconductor layer and a bandgap energy higher than that of the fourth nitride semiconductor layer. 4. The nitride semiconductor device according to claim 3, having a low p-type impurity concentration. 27. An n-type impurity concentration of the second nitride semiconductor layer, wherein an n-type impurity concentration of the first nitride semiconductor layer is in a range of 1 × 10 ¹⁷ / cm ³ to 1 × 10 ²⁰ / cm ^3. 1 × 1 impurity concentration
0 ¹⁹ / cm ³ or less, and the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 3
²⁰ / cm ³ or less, there is a nitride of claim 26, wherein the p-type impurity concentration of the fourth semiconductor layer is in the range of ^{1 × 10 18 / cm 3 ~1} × 10 21 / cm 3 Semiconductor element. 28. In the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and an n-type smaller than the second nitride semiconductor layer. An impurity concentration, and in the p-side strained superlattice layer, the third nitride semiconductor layer has a bandgap energy larger than that of the fourth nitride semiconductor layer and a bandgap energy higher than that of the fourth nitride semiconductor layer. 4. The nitride semiconductor device according to claim 3, having a high p-type impurity concentration. 29. An n-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³ or less, and an n-type impurity concentration of the second nitride semiconductor layer is 1 × 10 ¹⁷ / cm ^3. cm ³ to 1
And the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ²⁰ / cm ^3.
18 / cm ³ to 1 in the range of × 10 ²¹ / cm ^3, said fourth semiconductor according to claim 28, wherein the p-type impurity concentration of the nitride semiconductor layer is 1 × 10 ²⁰ / cm ³ or less element. 30. In the n-side strained superlattice layer, the first nitride semiconductor layer has a bandgap energy larger than that of the second nitride semiconductor layer and an n-type smaller than the second nitride semiconductor layer. An impurity concentration, and in the p-side strained superlattice layer, the third nitride semiconductor layer has a bandgap energy larger than that of the fourth nitride semiconductor layer and a bandgap energy higher than that of the fourth nitride semiconductor layer. 4. The nitride semiconductor device according to claim 3, having a low p-type impurity concentration. 31. An n-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁹ / cm ³ or less, and an n-type impurity concentration of the second nitride semiconductor layer is 1 × 10 ¹⁷ / cm ^3. cm ³ to 1
And the p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ²⁰ / cm ^3.
20 / cm ³ or less, there is a nitride of claim 30, wherein the p-type impurity concentration of the fourth semiconductor layer is in the range of ^{1 × 10 18 / cm 3 ~1} × 10 21 / cm 3 Semiconductor element. 32. In the n-side strained superlattice layer, the first nitride semiconductor layer is Al _Y Ga ₁ -YN (0 <Y <1).
And the second nitride semiconductor layer is made of In _x Ga ₁ -xN
(0 ≦ X <1), and in the p-side strained superlattice layer, the third nitride semiconductor layer is made of Al _Y Ga _1-Y N (0 <Y <1); 32. The nitride semiconductor device according to claim 24, wherein the nitride semiconductor layer is made of In _x Ga ₁ -xN (0 ≦ X <1). 33. The semiconductor device according to claim 24, wherein each of the second and fourth nitride semiconductor devices is made of GaN.
6. A nitride semiconductor device according to any one of the above. 34. In the n-side strained superlattice layer,
The first nitride semiconductor layer is Al_XGa_1-XN (0 <X <1)
Wherein the second nitride semiconductor layer is made of Al _YGa_1-YN
(0 <Y <1, X> Y), and in the p-side strained superlattice layer, the third nitride semiconductor
Body layer is Al_XGa_1-XN (0 <X <1),
The nitride semiconductor layer of No. 4 is made of Al_YGa_1-YN (0 <Y <1, X
> Y) according to one of the claims 24-31.
Nitride semiconductor device. 35. The nitride according to claim 24, wherein the first nitride semiconductor layer or the second nitride semiconductor layer is an undoped layer not doped with an n-type impurity. Semiconductor device. 36. The nitride according to claim 24, wherein the third nitride semiconductor layer or the fourth nitride semiconductor layer is an undoped layer not doped with a p-type impurity. Semiconductor device. 37. The nitride semiconductor device according to claim 1, wherein the active layer includes an InGaN layer. 38. The nitride semiconductor device according to claim 37, wherein said InGaN layer is a quantum well layer. 39. The nitride semiconductor device, wherein the active layer is a laser oscillation device located between a p-side clad layer and an n-side clad layer, wherein the active layer is one of the p-side clad layer and the n-side clad layer. 39. The nitride semiconductor device according to claim 1, wherein at least one of the layers is the n-side strain superlattice layer or the p-side strain superlattice layer. 40. The nitride semiconductor device is a laser oscillation device, wherein at least one of In between at least one of between the p-side cladding layer and the active layer or between the p-side cladding layer and the active layer. Containing nitride semiconductor or GaN and having an impurity concentration of 1 × 1
4. A light guide layer having a thickness of 0 ¹⁹ / cm ³ or less is formed.
10. The nitride semiconductor device according to item 9. 41. The nitride semiconductor device according to claim 40, wherein the light guide layer has a superlattice structure. 42. A gap between the light guide layer and the active layer, which has a larger band gap energy than the well layer of the active layer and the light guide layer, and has a thickness of 0.1 μm.
42. The nitride semiconductor device according to claim 40, wherein a cap layer made of the following nitride semiconductor is formed, and an impurity concentration of the cap layer is 1 × 10 ¹⁸ / cm ³ or more. 43. The nitride semiconductor device according to claim 42, wherein the light guide layer and the cap layer are formed on a p-conductive side nitride semiconductor layer side. 44. A nitride semiconductor layer is grown on a heterogeneous substrate made of a material different from a nitride semiconductor, and a surface of the nitride semiconductor layer is partially exposed on the grown nitride semiconductor layer. After forming a protective film as described above, on a nitride semiconductor substrate composed of a nitride semiconductor layer grown to cover the protective film from the exposed nitride semiconductor layer, any one of claims 1 to 43 A nitride semiconductor device formed from the nitride semiconductor device according to any one of the above.