JP2002164572A - Nitride semiconductor light emitting device - Google Patents

Abstract

[PROBLEMS] To improve the output of a nitride semiconductor device such as an LED and an LD and to reduce Vf to improve the reliability of the device. SOLUTION: An undoped first nitride semiconductor layer, an n-conductivity type second nitride semiconductor layer doped with an n-type impurity, and an undoped A third nitride semiconductor layer, the second nitride semiconductor layer is a single layer, an n-electrode is formed on the second nitride semiconductor layer, and the first nitride semiconductor layer and the second And the third nitride semiconductor layer have the same composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In).
_{The present invention} relates to a nitride semiconductor light emitting device comprising _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) and used for a light emitting device such as a light emitting diode device and a laser diode device.

[0002]

2. Description of the Related Art A nitride semiconductor is a high-brightness pure green light emitting LE.
D and blue LEDs have already been put to practical use in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources. These LED elements basically have a buffer layer made of GaN on a sapphire substrate,
An n-side contact layer made of Si-doped GaN; an active layer made of InGaN having a single quantum well structure; a p-side clad layer made of Mg-doped AlGaN;
And a p-side contact layer made of N in order. At 20 mA, 5 mW for a blue LED with an emission wavelength of 450 nm, external quantum efficiency of 9.1%, 520 n
The green LED of 3 m has an excellent characteristic of 3 mW and an external quantum efficiency of 6.3%.

[0003] Further, the present applicant has 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) L74, Jp.
nJAppl.Phys.35 (1996) L217}. This laser element
Multiple quantum well structure (MQW: Multi-
It has a double hetero structure having an active layer of Quantum-Well, a threshold current of 610 mA, a threshold current density of 8.7 kA / cm ² , and a pulse width of 2 μs and a pulse period of 2 ms.
10 nm oscillation is shown. The present applicant has also succeeded for the first time in continuous oscillation at room temperature and has announced. {For example, Nikkei Electronics December 2, 1996 Technical Bulletin, Appl.Phys.L
ett.69 (1996) 3034-, Appl.Phys.Lett.69 (1996) 4056-
Etc.], the laser device exhibits continuous oscillation for 27 hours at 20 ° C., at a threshold current density of 3.6 kA / cm ² , a threshold voltage of 5.5 V, and an output of 1.5 mW.

[0004]

As described above, nitride semiconductors have already been put to practical use in LEDs, and LDs have reached continuous oscillation for several tens of hours. However, LEDs have been used, for example, as a light source for illumination and an outdoor display exposed to direct sunlight. In order to achieve the same, the output needs to be further improved. Further, in order to reduce the threshold value of the LD to extend its life and to put it to practical use as a light source such as an optical pickup, further improvement is required. The LED element has a Vf of 3 at 20 mA.
It is near 6V. By further lowering Vf, the amount of heat generated by the element is reduced, and the reliability is improved. In a laser device, lowering the voltage at the threshold is very important for improving the life of the device. The present invention has been made in view of such circumstances, and a purpose thereof is to mainly improve the output of nitride semiconductor devices such as LEDs and LDs, and reduce Vf to reduce the reliability of the devices. To improve the performance.

[0005]

According to a first aspect of the present invention, there is provided a nitride semiconductor device comprising: an undoped first nitride semiconductor layer between a substrate and an active layer;
A second nitride semiconductor layer of an n-conductivity type doped with a type impurity and a third nitride semiconductor layer of an undoped type, wherein the second nitride semiconductor layer is a single layer; An n-electrode is formed on the first nitride semiconductor layer, and the first nitride semiconductor layer, the second nitride semiconductor layer, and the third nitride semiconductor layer have the same composition. Further, the nitride semiconductor light emitting device according to claim 2 according to the present invention is the nitride semiconductor light emitting device according to claim 1,
Wherein the nitride semiconductor layer, the second nitride semiconductor layer, and the third nitride semiconductor layer are made of GaN. Further, the nitride semiconductor light emitting device according to claim 3 according to the present invention is characterized in that in the nitride semiconductor light emitting device according to claim 1 or 2, the second nitride semiconductor layer has a superlattice structure. And Still further, in the nitride semiconductor light emitting device according to claim 4 of the present invention, the undoped first nitride semiconductor layer and the n-type impurity are doped between the substrate and the active layer in order from the substrate side. A second nitride semiconductor layer having an n-type conductivity and an undoped third nitride semiconductor layer, wherein the second nitride semiconductor layer is a single layer; An n-electrode is formed at the third
Is characterized in that the resistivity of the nitride semiconductor layer is larger than 0.1 Ω · cm. Further, in the nitride semiconductor light emitting device according to claim 5 according to the present invention, in the nitride semiconductor light emitting device according to claim 4, the third nitride semiconductor layer has
n _y Ga is InGaN represented by _1-y N, the I
The mixed crystal ratio y is 0.1 or less. In the nitride semiconductor light emitting device according to claim 6 of the present invention, an undoped first nitride semiconductor layer and an n-type impurity are sequentially doped between a substrate and an active layer from the substrate side. a second nitride semiconductor layer having an n-type conductivity and an undoped third nitride semiconductor layer, wherein the second nitride semiconductor layer is a single layer; An n-electrode is formed, and the first nitride semiconductor layer is made of AlGaN. Further, in the nitride semiconductor light emitting device according to claim 7 according to the present invention, in the nitride semiconductor light emitting device according to claim 6, the first nitride semiconductor layer includes:
Wherein the X value is 0.2 or less _{Al X Ga 1-X} N. The nitride semiconductor light emitting device according to claim 8 according to the present invention is the nitride semiconductor light emitting device according to claim 6 or 7, wherein the resistivity of the third nitride semiconductor layer is 0.1 Ω · cm. Furthermore, the nitride semiconductor light emitting device according to claim 9 according to the present invention is the nitride semiconductor light emitting device according to any one of claims 1 to 8, wherein the substrate and the first nitride A buffer layer grown between the semiconductor layer and the first nitride semiconductor layer at a lower temperature than the first nitride semiconductor layer. The nitride semiconductor light emitting device according to claim 10 according to the present invention is the nitride semiconductor light emitting device according to any one of claims 1 to 9, wherein the thickness of the third nitride semiconductor layer is Is 0.5 μm or less. In the present invention, the undoped nitride semiconductor layer refers to a nitride semiconductor layer that is not intentionally doped with impurities, for example, an impurity contained in a raw material, contamination in a reaction apparatus, or another layer intentionally doped with impurities. A layer in which impurities are mixed by unintended diffusion from a layer and a layer which can be regarded as substantially undoped by a small amount of doping (for example, a resistivity of 3 × 10 3
-1Ω · cm or more) is defined as undoped in the present invention.

The resistivity of the second nitride semiconductor layer is preferably less than 8 × 10 ⁻³ Ω · cm. When the resistivity of the second nitride semiconductor layer is 8 × 10 ⁻³ Ω · cm or more, Vf tends to not decrease much. A more preferable range of the resistivity is 6 × 10 ⁻³ Ω · cm or less, and further preferably 4 × 10 ⁻³ Ω · cm or less. The lower limit is not particularly limited, but is preferably adjusted to 1 × 10 ⁻⁵ Ω · cm or more. When the second nitride semiconductor layer is formed as a single layer, the lower limit is 1 × 10 ⁻³ Ω · cm or more. It is desirable to adjust to ^-5 Ω · cm or more. The superlattice layer has a film thickness of 10
It refers to a multilayer structure in which nitride semiconductor layers having a thickness of 0 Å or less, more preferably 70 Å, and most preferably 50 Å or less are stacked. If the resistance is lower than the lower limit, the amount of impurities such as Si, Ge, and Sn becomes too large, and the crystallinity of the nitride semiconductor tends to deteriorate.

Further, it is preferable that a buffer layer that is grown at a lower temperature than the first nitride semiconductor layer is provided between the substrate and the first nitride semiconductor layer. This buffer layer is made of, for example, AlN, GaN, AlGaN, or the like.
It can be grown at a temperature of 0 ° C. to 900 ° C. with a film thickness of 0.5 μm or less, to reduce lattice mismatch between the substrate and the nitride semiconductor, or to grow the first nitride semiconductor layer with good crystallinity. Acts as an underlayer.

Furthermore, it is preferable that the thickness of the third nitride semiconductor layer is 0.5 μm or less. The more preferable thickness of the third nitride semiconductor layer is adjusted to 0.2 μm or less, more preferably 0.15 μm or less. The lower limit is not particularly limited, but is 10 Å or more, preferably 50 Å.
It is desirable to adjust the thickness to Å or more, most preferably 100 Å or more. The third nitride semiconductor layer is an undoped layer having a resistivity of usually 0.1
Since it is as high as Ω · cm or more, when this layer is grown as a thick layer, Vf tends to be hardly reduced.

Further, a nitride semiconductor light emitting device of the present invention
Between the substrate and the active layer, in order from the substrate side, a first nitride semiconductor layer having a higher resistivity, and a second nitride semiconductor layer doped with an n-type impurity and having a resistivity smaller than that of the first nitride semiconductor layer. It has a nitride semiconductor layer and a third nitride semiconductor layer having a resistivity higher than that of the second nitride semiconductor layer, and an n-electrode is formed on the second nitride semiconductor layer. And
The first and third nitride semiconductor layers are, for example, undoped and have a resistivity greater than, for example, 0.1 Ω · cm, and the second nitride semiconductor layer is, for example, doped with an n-type impurity to have a resistivity. It can be smaller than 8 × 10 ⁻³ Ω · cm.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light emitting device according to the present invention has a nitride semiconductor layer having at least a three-layer structure between an active layer and a substrate. First, the first nitride semiconductor layer is undoped in order to grow the second nitride semiconductor layer containing an n-type impurity with good crystallinity. If this layer is intentionally doped with impurities, the crystallinity is deteriorated, and it is difficult to grow the second nitride semiconductor layer with good crystallinity. Next, the second nitride semiconductor layer is doped with an n-type impurity, and functions as a contact layer for forming an n-electrode having a low resistivity and a high carrier concentration. Therefore, the resistivity of the second nitride semiconductor layer is desirably as small as possible in order to obtain a preferable ohmic contact with the n-electrode material, and is preferably less than 8 × 10 ⁻³ Ω · cm. Next, the third nitride semiconductor layer is also undoped. The reason why this layer is undoped is that the second nitride semiconductor layer having a low resistivity and a high carrier concentration has poor crystallinity. Directly on this,
When the active layer, the clad layer, and the like are grown, the crystallinity of those layers is also deteriorated. Therefore, the undoped third nitride semiconductor having good crystallinity is interposed therebetween, so that the active layer before the growth of the active layer is formed. Acts as a buffer layer. Further, by interposing an undoped layer having a relatively high resistivity between the active layer and the second nitride semiconductor layer, it is possible to prevent a leak current of the element and increase a reverse breakdown voltage. Note that the carrier concentration of the second nitride semiconductor layer is 3 ×
It tends to be larger than 10 ¹⁸ / cm ³ . The active layer is an undoped nitride semiconductor containing In, preferably I
It is desirable to have a single quantum well structure having a well layer made of nGaN or a multiple quantum well structure. As the n-type impurity, a Group 4 element can be cited.
i or Ge, more preferably, Si is used.

[0011]

[Embodiment 1] FIG. 1 is a schematic sectional view showing the structure of an LED device according to an embodiment of the present invention. Hereinafter, a method of manufacturing the device of the present invention will be described with reference to this drawing. .

A substrate 1 made of sapphire (C-plane) is set in a reaction vessel, and after sufficiently replacing the inside of the vessel with hydrogen, the temperature of the substrate is increased to 1050 ° C. while flowing hydrogen to clean the substrate. . Another sapphire C face substrate 1, a sapphire having the principal R-plane, A plane, other, including other insulating substrate such as spinel _{(MgA1 2 O 4), SiC} (6H, 4H, and 3C ), Si, Zn
A semiconductor substrate such as O, GaAs, or GaN can be used.

(Buffer Layer 2) Subsequently, the temperature is set to 510 ° C.
The buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of about 200 angstroms using hydrogen as a carrier gas and ammonia and TMG (trimethylgallium) as a source gas.

(First Nitride Semiconductor Layer 3) Buffer Layer 2
After growth, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C, TM
Using G and ammonia gas, a first nitride semiconductor layer 3 made of undoped GaN is grown to a thickness of 1.5 μm. The first nitride semiconductor layer 3 is grown at a higher temperature, for example, 900 ° C. to 1100 ° C. than the buffer layer directly grown on the substrate, and is made of In _x Al _Y Ga ₁ -XYN (0 ≦ X, 0 ≦ Y, X + Y).
≦ 1), and the composition thereof is not particularly limited, but is preferably GaN, Al _x Ga having an X value of 0.2 or less.
_{With 1-} XN, a nitride semiconductor layer with few crystal defects can be easily obtained. The film thickness is not particularly limited, and the film is grown as a thicker film than the buffer layer, and is usually 0.1 μm or more and 20 μm or more.
It is grown with the following film thickness. Since this layer is an undoped layer, the resistivity is greater than 0.1 Ω · cm. Also the first
Since the nitride semiconductor layer 3 is a layer grown at a higher temperature than the buffer layer, it is distinguished from the buffer layer even when undoped.

(Second nitride semiconductor layer 4)
At 0 ° C., a second nitride semiconductor layer 3 made of Si-doped GaN is grown to a thickness of 3 μm using TMG and ammonia gas as the source gas and silane gas as the impurity gas. Similarly to the first nitride semiconductor layer, the second nitride semiconductor layer 3 is made of In _x Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1), and the composition thereof is not particularly limited, but is preferably GaN, Al _x Ga having an X value of 0.2 or less.
_{With 1-} XN, a nitride semiconductor layer with few crystal defects can be easily obtained. There is no particular limitation on the film thickness, but since it is a layer for forming an n-electrode, it is preferable to grow the film to a film thickness of 1 μm or more and 20 μm or less. In addition, using another sapphire substrate not having an element structure, a wafer grown to the second nitride semiconductor layer in the same manner was prepared, and the resistivity of the second nitride semiconductor layer was measured to be 5 × 10 ^−3. Ω · cm.

The second nitride semiconductor layer has a superlattice structure in which two types of nitride semiconductor layers having different band gap energies are laminated, or in which nitride semiconductor layers having the same composition are laminated. It is good. When a superlattice layer is used, the mobility of the second nitride semiconductor layer is increased and the resistivity is further reduced, so that a device with particularly high luminous efficiency can be realized. In the case of a superlattice structure, the thickness of the nitride semiconductor layer forming the superlattice is 100 Å or less, more preferably 70 Å or less,
Most preferably, it is adjusted to 50 Å or less.
In the case of a superlattice structure, the nitride semiconductor layer forming the superlattice may be modulation-doped with Si, Ge, Sn, S, or the like. Modulation doping means that the nitride semiconductor layers forming the superlattice layer have different impurity concentrations from each other. In this case,
One layer may be undoped, that is, undoped. Preferably, the second nitride semiconductor layer has a superlattice structure in which layers having different band gap energies are stacked, and one of the nitride semiconductor layers is desirably heavily doped with an n-type impurity. Preferably, the semiconductor layer is undoped. When performing modulation doping, the difference in impurity concentration is desirably one digit or more.

(Third nitride semiconductor layer 5) Next, only silane gas is stopped, and undoped Ga
A third nitride semiconductor layer 5 made of N is grown to a thickness of 0.15 μm. This third nitride semiconductor layer 5 is also made of In _X
It can be composed of Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and its composition is not particularly limited.
aN, X value of 0.2 or less of AlXGa1-XN or Y value is 0.1 or less In _Y Ga _1-Y N with the nitride semiconductor layer is easily obtained with less crystal defects. When InGaN is grown, it is possible to prevent cracks in the Al-containing nitride semiconductor layer when growing a nitride semiconductor containing Al thereon. Note that when the second nitride semiconductor layer is grown using a single nitride semiconductor, the first nitride semiconductor layer, the second nitride semiconductor layer, and the third nitride semiconductor layer have the same composition. It is desirable to grow a nitride semiconductor.

(Active Layer 6) Next, the temperature is set to 800 ° C., the carrier gas is switched to nitrogen, and TMG, TMI
An active layer 6 having a single quantum well structure is grown by growing an undoped In _0.4 Ga _0.6 N layer with a thickness of 30 Å using (trimethylindium) and ammonia.

(P-side cladding layer 7)
0 ℃, TMG, TMA, ammonia, Cp2Mg
Using (cyclopentadienyl magnesium), a p-side cladding layer 7 of p-type Al _0.1 Ga _0.9 N doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. This layer acts as a carrier confinement layer, and is a nitride semiconductor containing Al, preferably Al _Y Ga _1-Y N (0 <Y
It is desirable to grow <1). In order to grow a layer having good crystallinity, Al _Y Ga ₁ -YN having a Y value of 0.3 or less is preferred.
It is desirable to grow the layer to a thickness of 0.5 μm or less.

(P-side contact layer 8) Subsequently, at 1050 ° C.
And using TMG, ammonia and Cp ₂ Mg,
A p-side contact layer 8 made of p-type GaN doped with × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. The p-side contact layer 8 is also formed of In _X Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1), and the composition thereof is not particularly limited. However, when it is preferably GaN, a nitride semiconductor layer with few crystal defects is easily obtained, and a preferable ohmic contact with a p-electrode material is easily obtained.

After the reaction is completed, the temperature is lowered to room temperature, and the wafer is placed in a reaction vessel in a nitrogen atmosphere at a temperature of 700.degree.
Anneal at ℃ to further reduce the resistance of the p-type layer.

After annealing, the wafer is taken out of the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer 8, and etching is performed from the p-side contact layer side by an RIE (reactive ion etching) apparatus. Do
As shown in FIG. 1, the surface of the second nitride semiconductor layer 4 is exposed.

After the etching, almost all of the uppermost p-side contact layer is formed of a light-transmitting p-electrode 9 containing 200 Å of Ni and Au, and a bonding Au on the p-electrode 9. p pad electrode 10
It is formed with a film thickness of μm. On the other hand, the surface of the second nitride semiconductor layer 4 exposed by etching has n containing W and Al
The electrode 11 is formed. Finally, an insulating film 12 made of SiO ₂ is formed as shown in FIG. 1 to protect the surface of the p-electrode 9, and the wafer is separated by scribing to form a film 35.
An LED element of 0 μm square is used.

This LED device emits pure green light of 520 nm at a forward voltage of 20 mA, and has a buffer layer made of GaN on a sapphire substrate, an n-side contact layer made of Si-doped GaN, and an InG having a single quantum well structure.
Compared to a conventional green light emitting LED in which an active layer made of aN, a p-side clad layer made of Mg-doped AlGaN, and a p-side contact layer made of Mg-doped GaN are sequentially stacked, the Vf at 20 mA is 0.1 The output was improved by about 0.2 V and the output by 5% to 10%.

[Embodiment 2] FIG. 2 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention, which is taken when the device is cut in a direction perpendicular to the resonance direction of laser light. 3 shows the structure. Hereinafter, a second embodiment will be described with reference to this drawing.

On the substrate 20 made of sapphire (C-plane), a buffer layer 21 is grown to a thickness of 200 angstroms in the same manner as in the first embodiment.

(First Nitride Semiconductor Layer 22) After the growth of the buffer layer 20, the temperature is increased to 1020 ° C.
At 5 ° C., a first nitride semiconductor layer 22 made of undoped GaN is grown to a thickness of 5 μm.

(Second nitride semiconductor layer 23)
At 020 ° C., a second nitride semiconductor layer made of n-type GaN doped with Si using a silane gas as an impurity gas is 3 μm.
It is grown to a thickness of m. The resistivity of the second nitride semiconductor layer was also 5 × 10 ⁻³ Ω · cm.

(Third Nitride Semiconductor Layer 24) Next, the temperature is set to 800 ° C., and the third nitride semiconductor layer 24 made of undoped In _0.05 Ga _0.95 N is formed using TMG, TMI, and ammonia by 500 Å. It grows with the film thickness of.

(N-side cladding layer 25)
0 ° C and TMA, TMG, NH ₃ , Si
N-type Al doped with 1 × 10 ¹⁷ / cm ³ using H _4
An n-side clad layer having a superlattice structure in which 40 Å of _0.25 Ga _0.75 N layers and 40 Å of undoped GaN layers are alternately stacked is grown. This n-side cladding layer acts as a carrier confinement layer and a light confinement layer.

(N-side light guide layer 26)
An n-side optical guide layer 26 of n-type GaN doped with Si at 1 × 10 ¹⁹ / cm ³ is grown at a temperature of 0.2 ° C. to a thickness of 0.2 μm. The n-side light guide layer 26 functions as a light guide layer of an active layer, and is preferably used to grow GaN or InGaN, and is usually grown to a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. desirable. This n-side light guide layer may be undoped.

(Active Layer 27) At a temperature of 800 ° C., a well layer made of Si-doped In _0.2 Ga _0.8 N is grown to a thickness of 25 Å. Next, only by changing the molar ratio of TMI, the Si-doped In _0.01
A barrier layer made of Ga _0.99 N is grown to a thickness of 50 Å. This operation is repeated twice to finally form a multiple quantum well structure in which well layers are stacked.

(P-side cap layer 28)
20 ° C, TMG, TMA, ammonia, Cp ₂ M
with g, the band gap energy than the active layer is large, Al _0.3 Ga was 1 × 10 ²⁰ / cm3 doped with Mg
_A p-side cap layer 28 of _0.7 N is grown to a thickness of 300 Å. The p-side cap layer 28 is preferably of a p-type, but may be of an i-type in which the carrier is compensated by doping an n-type impurity due to its small thickness.
The thickness of the p-side cap layer 28 is adjusted to 0.1 μm or less, more preferably 500 Å or less, and most preferably 300 Å or less. This is because if the layer is grown with a thickness greater than 0.1 μm, cracks are easily formed in the p-side cap layer 28, and it is difficult to grow a nitride semiconductor layer having good crystallinity. In addition, carriers cannot pass through the energy barrier due to the tunnel effect. A
When the composition ratio of 1 is higher, the LD element is more likely to oscillate if it is formed thinner. For example, A with a Y value of 0.2 or more
In the case of l _Y Ga _{1 -Y} N, it is desirable to adjust the thickness to 500 Å or less. Although the lower limit of the film thickness of the p-side cap layer 28 is not particularly limited, it is preferable that the film be formed with a film thickness of 10 Å or more.

(P-side light guide layer 29)
A p-side light guide layer 26 made of GaN doped with Mg at 1 × 10 ¹⁸ / cm ³ is grown at 0.2 ° C. to a thickness of 0.2 μm. The p-side light guide layer 29 acts as a light guide layer of an active layer, like the n-side light guide layer 26, and serves as a GaN, I
It is desirable to grow nGaN, preferably to a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. The p-side light guide layer is doped with a p-type impurity, but may be made of an undoped nitride semiconductor.

(P-side cladding layer 30)
P-type Al doped with Mg at 1 × 10 ²⁰ / cm ³
_A p-side cladding layer 30 having a superlattice structure in which 40 layers of _0.25 Ga _0.75 N layers and 40 angstroms of undoped GaN layers are alternately laminated is grown. This p-side cladding layer acts as a carrier confinement layer and an optical confinement layer like the n-side cladding layer.
By making the side cladding layer side a superlattice, the resistance of the p-layer tends to decrease and the threshold value tends to decrease more.

(P-side contact layer 31) Finally, on the p-side cladding layer 30, Mg was added at 2 × 10 ²⁰ /
A p-side contact layer 31 made of GaN doped with cm ³ is grown to a thickness of 150 Å.

After the reaction is completed, the temperature is lowered to room temperature, and the wafer is placed in a nitrogen atmosphere in a reaction vessel.
Annealing is performed at ° C. to further reduce the resistance of the layer doped with the p-type impurity.

After annealing, the wafer was taken out of the reaction vessel and, as shown in FIG.
The side contact layer 31 and the p-side cladding layer 30 are etched to form a ridge shape having a stripe width of 4 μm. In particular, by forming a layer of a nitride semiconductor layer containing Al or higher which is higher than the active layer into a ridge shape, light emission of the active layer is concentrated on the lower portion of the ridge, the transverse mode is easily united, and the threshold value is lowered. Cheap. After the formation of the ridge, a mask is formed on the surface of the ridge, and the surface of the second nitride semiconductor layer 23 on which the n-electrode 34 is to be formed is exposed, as shown in FIG. Let it.

Next, a p-electrode 32 made of Ni and Au is formed on almost the entire upper surface of the ridge of the p-side contact layer 31. On the other hand, an n-electrode 34 made of Ti and Al is formed on almost the entire surface of the stripe-shaped second nitride semiconductor layer 23.
It should be noted that substantially the entire surface refers to an area of 80% or more. Thus, the second nitride semiconductor layer 2 is symmetrical with respect to the p-electrode 32.
Exposing 3 and providing an n-electrode on almost the entire surface of the second layer 23 is also very advantageous in lowering the threshold value. Further, after an insulating film 35 made of SiO ₂ is formed between the p electrode and the n electrode, the p pad electrode 3 made of Au is electrically connected to the p electrode 32 via the insulating film 35.
Form 3

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 20 on which the nitride semiconductor is not formed is wrapped using a diamond abrasive. The thickness of the substrate is 50 μm. After lapping, the substrate surface is mirror-finished by polishing with a finer abrasive at 1 μm.

After polishing the substrate, the polished surface 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 is formed, and finally the bar is cut in a direction parallel to the p-electrode 32 to form a laser device. When this device was placed on a heat sink and laser oscillation was attempted at room temperature, the threshold current density was 2.5 kA / c at room temperature.
At m ² and a threshold voltage of 4.0 V, continuous oscillation at an oscillation wavelength of 405 nm was confirmed. The lifetime was 500 hours or more, and the lifetime was improved 10 times or more as compared with the conventional nitride semiconductor laser device.

Example 3 In Example 1, the temperature was raised to 800 ° C. during the growth of the third nitride semiconductor
Undoped In _0.05 G using G, TMI and ammonia
An LED element was obtained in the same manner as in Example 1, except that a _0.95 N layer was grown to a thickness of 200 Å.
An element having substantially the same characteristics as in Example 1 was obtained.

[0043]

As described above, in the device of the present invention, the undoped first nitride semiconductor layer between the active layer and the substrate is the second nitride semiconductor doped with an n-type impurity. Then, the second nitride semiconductor layer doped with an n-type impurity can be grown as a thick film with good crystallinity. Further, the undoped third nitride semiconductor becomes an underlayer having good crystallinity for the nitride semiconductor layer grown on the third nitride semiconductor. Therefore, the resistivity of the second nitride semiconductor layer can be reduced and the carrier concentration can be increased, so that a very efficient nitride semiconductor element can be realized. As described above, according to the present invention, a light-emitting element having a low Vf and a low threshold value can be realized. Therefore, a heat generation amount of the element is reduced and an element with improved reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of an LED element according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a structure of a laser device according to another embodiment of the present invention.

[Explanation of symbols]

 1, 20 ... substrate 2, 21 ... buffer layer 3, 22 ... first nitride semiconductor layer 4, 23 ... second nitride semiconductor layer 5, 24 ... third Nitride semiconductor layer 6, 27 ... Active layer 7, 30 ... p-side cladding layer 8, 31 ... p-side contact layer 25 ... n-side light guide layer 26 ... n-side cladding layer 28 ... p-side cap layer 29 ... p-side light guide layer 9, 32 ... p-electrode 10, 33 ... p-pad electrode 11, 34 ... n-electrode 35 ... insulating film

Continued on the front page F term (reference) 5F041 AA24 CA05 CA34 CA40 CA46 CA65 5F073 AA13 AA45 AA74 CA07 CB05 CB07 DA05 DA35 EA23

Claims (10)

[Claims] An undoped first nitride semiconductor layer, an n-conductivity-type second nitride semiconductor layer doped with an n-type impurity, and an undoped layer between a substrate and an active layer in this order from a substrate side. A third nitride semiconductor layer, wherein the second nitride semiconductor layer is a single layer, an n-electrode is formed on the second nitride semiconductor layer, and the first nitride semiconductor layer Wherein the second nitride semiconductor layer and the third nitride semiconductor layer have the same composition. 2. The nitride semiconductor light emitting device according to claim 1, wherein said first nitride semiconductor layer, said second nitride semiconductor layer, and said third nitride semiconductor layer are made of GaN. . 3. The nitride semiconductor light emitting device according to claim 1, wherein said second nitride semiconductor layer has a superlattice structure. 4. An undoped first nitride semiconductor layer, an n-conductivity-type second nitride semiconductor layer doped with an n-type impurity, and an undoped layer between the substrate and the active layer in this order from the substrate side. A third nitride semiconductor layer, wherein the second nitride semiconductor layer is a single layer, an n-electrode is formed on the second nitride semiconductor layer, and the third nitride semiconductor layer Has a resistivity of 0.1Ω · cm
A nitride semiconductor light emitting device characterized by being larger than the above. 5. The method according to claim 1, wherein the third nitride semiconductor layer is made of In _y Ga.
The nitride semiconductor light emitting device according to claim 4, wherein the nitride semiconductor light emitting device is InGaN represented by _1-yN , and an In mixed crystal ratio y of the InGaN is 0.1 or less. 6. An undoped first nitride semiconductor layer, an n-type conductive second nitride semiconductor layer doped with an n-type impurity, and an undoped layer between the substrate and the active layer in this order from the substrate side. A third nitride semiconductor layer, wherein the second nitride semiconductor layer is a single layer, an n-electrode is formed on the second nitride semiconductor layer, and the first nitride semiconductor layer Is a nitride semiconductor light-emitting device. 7. The nitride semiconductor light emitting device according to claim 6, wherein said first nitride semiconductor layer is Al _X Ga _1-X N having an X value of 0.2 or less. 8. The resistivity of the third nitride semiconductor layer is:
The nitride semiconductor light-emitting device according to claim 6, wherein the nitride semiconductor light-emitting device is larger than 0.1 Ω · cm. 9. The semiconductor device according to claim 1, further comprising a buffer layer grown at a lower temperature than the first nitride semiconductor layer between the substrate and the first nitride semiconductor layer. The nitride semiconductor light emitting device according to any one of the above. 10. The nitride semiconductor light emitting device according to claim 1, wherein a thickness of said third nitride semiconductor layer is 0.5 μm or less.