JP2001203385A - Nitride semiconductor light emitting diode - Google Patents

Abstract

(57) [Problem] To provide a nitride semiconductor light emitting diode having a light emission peak wavelength of 370 nm or less that can obtain good ohmic contact and suppress self absorption and improve light emission output. An active layer includes a nitride semiconductor layer having an emission peak wavelength of 370 nm or less, and a p-type contact layer includes a p-type contact layer.
Al _a containing p-type impurity at high concentration on the side in contact with the electrode
A _first p containing Ga _1-a N (0 ≦ a <0.05)
The first p-type contact layer, the first p-type contact layer being in contact with the first p-type contact layer on the active layer side of the first p-type contact layer, the p-type impurity having a lower concentration than the first p-type contact layer, and the Al composition ratio being the first.
Al _b Ga ₁ -bN (0 <b <
It is formed and a second p-type contact layer comprising a 0.1) will be, n-type contact layer further contact with the n _electrode, Al _d Ga _1-d N a (0 <d <0.1) Comprising.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor device (In _X Al _Y Ga ₁ ) used for a light emitting device such as a light emitting diode (LED), a laser diode (LD), a solar cell, an optical sensor, and a light receiving device. _-XY N, 0 ≦ X, 0 ≦ Y, X
+ Y ≦ 1), especially when the emission peak wavelength is 370 nm.
The present invention relates to the following nitride semiconductor light emitting diodes that emit light in the ultraviolet region.

[0002]

2. Description of the Related Art In recent years, ultraviolet LEDs have become practical. For example, Applied Physics, Vol. 68, No. 2 (199
9) On p152 to p155, on a sapphire substrate,
GaN buffer layer, n-type GaN contact layer (film thickness: 4
μm), n-type AlGaN cladding layer, undoped InG
aN active layer (In composition is almost zero), p-type AlG
aN cladding layer, p-type GaN contact layer (film thickness: 0.
12 μm) are described. And this ultraviolet LED, under certain conditions,
When the emission peak is 371 nm, the emission output is 5 mW. On the other hand, when the emission wavelength is shorter than this, self absorption occurs because the n-type and p-type contact layers are GaN, and the emission output is reduced. It is stated that it will drop sharply. Furthermore, in order to prevent the reduction of the light emission output and to shorten the oscillation wavelength, it is suggested that the self absorption can be prevented by using AlGaN for the n-type and p-type contact layers.

[0003]

However, simply,
A having a high Al composition ratio enough to prevent self-absorption sufficiently
When the contact layer is grown with lGaN, it becomes difficult to obtain good ohmic contact with the electrode. This is probably because AlGaN physically inactivates the dopant or changes in the work function with the metal serving as the electrode due to fluctuations in the Fermi level. It is considered that ohmic contact may not be easily obtained. Such a decrease in ohmic contact is large in the p-type contact layer. Also, as described above, if the contact layer is doped with a large amount of impurities in order to improve the point where the inclusion of the Al composition causes inactivation of the dopant and makes it difficult to obtain an ohmic contact, the amount of the impurities is substantially proportional to the amount of the impurities. As a result, impurity levels are formed, so that self-absorption increases, and the light emission output may decrease due to a decrease in crystallinity.

Further, it is conceivable that the contact layer is made of GaN and the film thickness is reduced to reduce the self-absorption relatively. However, for example, when the film thickness of the p-type contact layer is reduced, the device characteristics are not sufficient. When the thickness of the n-type contact layer is reduced, the operation becomes complicated and it becomes difficult to expose the n-type contact layer.

[0005] As described above, in the light emitting diode having a light emission peak wavelength of 370 nm or less in the related art, self-absorption occurs in the contact layer and the light emission output is reduced.
If the contact layer is simply grown as AlGaN to prevent self-absorption by GaN, ohmic contact will be reduced. If the doping amount of impurities is further increased to obtain ohmic contact, the formation of impurity levels and the formation of crystal defects will occur. The increase causes self-absorption. Therefore, it is desired that ohmic contact be improved while preventing self-absorption.

Accordingly, an object of the present invention is to provide a nitride semiconductor light emitting diode having a light emission peak wavelength of 370 nm or less capable of obtaining good ohmic contact and suppressing self-absorption and improving light emission output. is there.

[0007]

That is, the present invention can achieve the object of the present invention by the following constitutions (1) to (6). (1) In a nitride semiconductor device having at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on a substrate, the active layer has an emission peak wavelength of 370n.
m or less, and as the p-type nitride semiconductor layer, a p-type contact layer in contact with a p-electrode has an Al _a containing a high concentration of p-type impurities on a side in contact with the p-electrode.
A _first p containing Ga _1-a N (0 ≦ a <0.05)
The first p-type contact layer, the first p-type contact layer being in contact with the first p-type contact layer on the active layer side of the first p-type contact layer, containing a p-type impurity at a lower concentration than the first p-type contact layer;
Al _b Ga having a higher l composition ratio than the first p-type contact layer
_A second p-type contact layer containing _1-bN (0 <b <0.1), and further, as the n-type nitride semiconductor layer, an n-type contact layer in contact with an n-electrode. Comprises Al _d Ga _1-d N (0 <d <0.1). (2) The nitride according to (1), wherein the first p-type contact layer in contact with the p-electrode contains a p-type impurity at 1 × 10 ¹⁹ to 1 × 10 ²² / cm ^3. Object semiconductor light emitting diode. (3) The nitride semiconductor light-emitting diode according to the above (1) or (2), wherein the second p-type contact layer contains a p-type impurity of 1 × 10 ²⁰ / cm ³ or less. . (4) The thickness of the first p-type contact layer in the p-type contact layer is 100 to 500 Å, and the thickness of the second p-type contact layer is 400
The nitride semiconductor light-emitting diode according to the above (1), which has a thickness of ２０００2000 Å. (5) The n-type contact layer contains 1 × 1 n-type impurities.
The nitride semiconductor light-emitting diode according to the above (4), which contains 0 ¹⁷ to 1 × 10 ¹⁹ / cm ³ . (6) Al is provided between the active layer and the n-type contact layer.
_e Ga _1-e N has a first nitride semiconductor layer comprises a (0 <e <0.3), further, between the active layer and the p-type contact layer, Al _f Ga _{1- f N (0 <f <0.4} ) nitride semiconductor light emitting diode according to (1), characterized in that it comprises a second nitride semiconductor layer comprises a.

That is, according to the present invention, the n-type contact layer is made of AlGaN having a specific Al composition ratio, and the p-type contact layer is formed of a first p-type contact layer having a high p-type impurity concentration and a small Al composition ratio. And a second p-type contact layer having a low p-type impurity concentration and a high Al composition ratio, and a first contact layer having a high p-type impurity concentration is formed on the side in contact with the p-electrode. A good ohmic contact can be obtained and self-absorption can be suppressed, and a nitride semiconductor light emitting diode having a good emission output and a light emission peak wavelength of 370 nm or less can be obtained. Here, in the present invention, the high or low p-type impurity concentration in the p-type contact layer and the high or low Al composition ratio mean that
The relative relationship between a first p-type contact layer and a second p-type contact layer that constitute a p-type contact layer is shown.

The present inventors have made various studies on the point that as described above, simply including an Al composition to prevent self-absorption causes a decrease in ohmic contact due to inactivation of impurities and the like. As a result, the n-type contact layer is made of AlGaN having a specific Al composition ratio, and the p-type contact layer has a two-layer structure of a layer for obtaining ohmic contact and a layer for securing a film thickness for maintaining device characteristics. Thought about doing it. The present inventor has proposed that the first p-type electrode having a high p-type impurity concentration and a low p-electrode ratio in contact with the p-electrode having a low Al composition ratio as described above
Forming a p-type contact layer with the p-type contact layer and a second p-type contact layer having a low impurity concentration and a high Al composition ratio, and further combining the n-type contact layer with a specific Al composition ratio to form an ohmic contact And it was possible to prevent self-absorption, thereby achieving a nitride semiconductor light emitting diode having a good light emission output.

Further, in the present invention, the first p-type
The tact layer contains 1 × 10 p-type impurities. ¹⁹~ 1 × 10^{twenty two}/ C
m^Three, Preferably 5 × 10²⁰~ 5 × 10^{twenty one}/ Cm^ThreeContains
Is preferable in that good ohmic contact is obtained.
Still further, in the present invention, the second p-type contact layer
Has a p-type impurity of 1 × 10²⁰/ Cm^ThreeBelow, preferably
5 × 10¹⁸~ 5 × 10¹⁹/ Cm^ThreeIf contained, the element
To maintain the characteristics, increase the thickness of the p-type contact layer.
However, it is preferable in that self absorption can be prevented.

Further, in the present invention, the thickness of the first p-type contact layer in the p-type contact layer is 100
~ 500 angstroms, preferably 150-300
When the thickness is angstrom, even if the p-type impurity concentration is increased, the self-absorption due to the impurity level can be relatively reduced and the ohmic contact with the p-electrode can be improved if the film thickness is set to be small. The second p-type contact layer has a thickness of 400 to 2,000 angstroms;
Preferably, the thickness is from 800 to 1200 angstroms to prevent self-absorption and maintain device characteristics.

Further, according to the present invention, the n-type contact layer containing Al has an n-type impurity concentration of 1 × 10 ¹⁷ to 1 × 1.
0 ¹⁹ / cm ³ , preferably 1 × 10 ¹⁸ to 1 × 10 ¹⁹ / c
m ³ is preferable in terms of preventing self-absorption, maintaining ohmic contact, and improving light emission output. As described above, when the Al composition ratio of the n-type contact layer and the n-type impurity concentration are specified and combined, as in the case of the p-type contact layer, it is preferable in terms of ohmic contact and crack prevention and improvement in light emission output. .

Further, according to the present invention, a first nitride semiconductor layer containing Al _e Ga _{1 -e} N (0 <e <0.3) is provided between the active layer and the n-type contact layer. has further between the active layer and the p-type contact _{layer, Al f Ga 1-f N} (0
By having the second nitride semiconductor layer containing <f <0.4), the confinement of carriers in the active layer can be improved,
It is preferable from the viewpoint of improving light emission output. Further, when the Al composition ratio of each of the first nitride semiconductor layer and the second nitride semiconductor layer is set in the above range and the Al composition ratio and the impurity concentration of the contact layer are combined, the prevention of crack generation,
Ohmic contact can be made favorable, which is preferable in terms of improvement in light emission output. Since the first nitride semiconductor layer and the second nitride semiconductor layer have a function as a clad layer, in the present invention, the first nitride semiconductor layer is hereinafter referred to as an n-type clad layer, The nitride semiconductor layer is a p-type cladding layer. However, it is not limited to this.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to FIG. FIG. 1 is a schematic sectional view of a nitride semiconductor device according to one embodiment of the present invention. In FIG.
On a substrate 1, a buffer layer 2, Al _d Ga _1-d N (0 <d <
0.1), n-type contact layer 3, Al _e Ga
N _- type cladding layer 4 containing _1-e N (0 <e <0.3); active layer 5 of In _g Ga _1-g N (0 ≦ g <0.1);
a p-type cladding layer 6 containing l _f Ga _1-f N (0 <f <0.4), a second p-type cladding layer containing Al _b Ga _1-b N (0 <b <0.1) Type contact layer 7b and Al _a Ga _1-a N
A nitride semiconductor device having a p-type contact layer 7 composed of a first p-type contact layer 7a containing (0 ≦ a <0.05) and having an emission peak wavelength of 370 nm or less is described. ing. Then, the n-type contact layer 3
, An n-electrode is formed in contact with the first p-type contact layer 7 a of the p-type contact layer 7.
First, the n-type contact layer 3 and the p-type contact layer 7 of the present invention will be described.

[N-type contact layer 3] In the present invention,
As the n-type contact layer 3, at least Al_dGa_1-d
N (0 <d <0.1, preferably 0.01 <d <0.0
5) A nitride semiconductor layer comprising: Al composition ratio is
When the content is within the above range, the crystallinity and the ohmic property are prevented while the self-absorption is prevented.
This is preferable in terms of sonic contact. Further, the n-type contact
Layer 3 contains 1 × 10 n-type impurities.¹⁷~ 1 × 10¹⁹/ C
m ^Three, Preferably 1 × 10¹⁸~ 1 × 10¹⁹/ Cm^ThreeConcentration of
If contained, maintain ohmic contact and crack
It is preferable in terms of prevention of production and maintenance of crystallinity. Thus n
Composition ratio and n-type impurity concentration of the n-type contact layer
The combination of can prevent self-absorption and
It is preferable from the viewpoint of preventing a mic contact and a crack. n-type impurity
Is not particularly limited, for example, Si, Ge, etc.
And preferably Si. n-type contact layer
The film thickness of No. 3 is not particularly limited, but is preferably 0.1 to 20 μm.
Preferably, it is 1 to 10 μm. Film thickness
Within this range, the vicinity of the interface (for example, with the n-type cladding layer)
Of the crystallinity (as a base) and the decrease in resistivity
It is preferred in that respect.

[P-type contact layer 7] In the present invention,
As the p-type contact layer 7, at least a first p-type contact layer 7a having a high p-type impurity concentration and a low Al composition ratio in contact with a p-electrode and a second p-type contact layer having a low p-type impurity concentration and a high Al composition ratio are provided. It is formed from the contact layer 7b. As described above, by forming the p-type contact layer 7 with two types of layers having different p-type impurity concentrations and Al composition ratios, a good ohmic contact can be obtained with the first p-type contact layer 7a. When the p-type contact layer is adjusted to a thickness that can maintain the device characteristics, even when the thickness of the second p-type contact layer 7b is increased, the self-absorption can be prevented because the Al composition ratio is high. . In other words, in the p-type contact layer 7, the first p-type contact layer 7a for obtaining ohmic contact and the second p-type contact layer 7 for securing the film thickness to the extent that the device characteristics can be maintained while preventing self absorption. It is composed of two layers including a contact layer 7b. Hereinafter, the first p-type contact layer 7a and the second p-type contact layer 7b will be described. First p-type contact layer 7
“a” has a higher impurity concentration and a lower Al composition ratio than the second p-type contact layer 7b.

As such a first p-type contact layer 7a, a nitride semiconductor containing Al _a Ga _1-a N (0 ≦ a <0.05, preferably 0 <a <0.01) Layers can be mentioned. When the Al composition ratio is within the above range, even if the p-type impurity concentration is highly doped, inactivation of the impurity can be prevented, and favorable ohmic contact with the p-electrode can be obtained, which is preferable. Also, the first p-type contact layer 7a
Is preferable in terms of prevention of self-absorption when the Al content is within the above range, and is also preferable in terms of crystallinity. The Al composition ratio of the first p-type contact layer 7a is adjusted to be lower than the Al composition ratio of the second p-type contact layer 7b within the above range.

Examples of the p-type impurity concentration of the first p-type contact layer 7a, is not particularly limited, but preferably the degree to which ohmic contact with the p electrode can be obtained satisfactorily, for example specifically, 1 × 10 ¹⁹ ~ It is 1 × 10 ²² / cm ³ , preferably 5 × 10 ^{20 to} 5 × 10 ²¹ / cm ³ . When the p-type impurity concentration is within the above range, good ohmic contact can be obtained, which is preferable. The p-type impurity concentration of the first p-type contact layer 7a is within the above range,
It is adjusted to be higher than the impurity concentration of b. Also,
The thickness of the first p-type contact layer 7a is not particularly limited, but may be any thickness that allows good ohmic contact with the p-electrode. For example, specifically, 100 to 5
00 angstrom, preferably 150-300 angstrom. With such a film thickness, even if the Al composition ratio is reduced, the film thickness is relatively small, so that self absorption can be prevented. Further, a high ohmic contact is obtained by containing a high concentration of p-type impurities. preferable.

Next, as the second p-type contact layer 7b, Al _b Ga ₁ -bN (0 <b <0.1, preferably 0.
01 <b <0.05). When the Al composition ratio is in the above range, it is preferable in terms of prevention of self-absorption as in the case of the n-type contact layer, and furthermore, it is also preferable in terms of crystallinity and ohmic contact. Also,
The Al composition ratio of the second p-type contact layer 7b is adjusted to be higher than that of the first p-type contact layer 7a within the above range. The p-type impurity concentration of the second p-type contact layer 7b is desirably contained to such an extent that the second p-type contact layer 7b exhibits p-type.
× 10 ²⁰ / cm ³ or less, preferably 5 × 10 ^{18 to} 5 × 1
0 ¹⁹ / cm ³ . It is preferable that the p-type impurity concentration is in the above range in order to prevent self-absorption by forming impurity levels. The p-type impurity concentration of the second p-type contact layer 7b is adjusted to be lower than that of the first p-type contact layer 7a within the above range.

The thickness of the second p-type contact layer 7b is not particularly limited.
Is between 400 and 1200 angstroms, preferably 80
0 to 1200 angstroms. It is preferable that the thickness of the second p-type contact layer 7b be within the above range, since the thickness can be adjusted to a level that can maintain the device characteristics while preventing self-absorption. The p-type impurity contained in the p-type contact layer 7 is not particularly limited, but preferably includes, for example, Mg.

Here, as described above, the first p-type contact layer 7a and the second p-type contact layer 7b constituting the p-type contact layer 7 have the same impurity concentration and Al composition ratio. However, the first p-type contact layer 7a is adjusted to have a higher impurity concentration and a lower Al composition ratio with respect to the second p-type contact layer 7b within the described ranges. Thereby, a good effect can be obtained. If the p-type contact layer 7 is formed of only a layer having a low Al composition ratio or only a layer having a high impurity concentration, good ohmic contact can be obtained but self-absorption cannot be sufficiently prevented. It becomes difficult to obtain both prevention of self-absorption together with ohmic contact. In the p-type contact layer 7, a good ohmic contact is obtained by the first p-type contact layer 7a having a high p-type impurity concentration and a small Al composition ratio, and the second p-type contact layer 7 has a low p-type impurity concentration and a large Al composition ratio. The structure is such that ohmic contact and prevention of self-absorption are obtained by the respective layers such that self-absorption can be prevented and element characteristics can be maintained by the p-type contact layer 7b. Then, the layers of the first p-type contact layer 7a and the second p-type contact layer 7b act synergistically to obtain an element having good light emission output by good ohmic contact and prevention of self-absorption. it can. Further, in the current nitride semiconductor, it is more difficult to form the p-type than the n-type, and it is important to prevent the p-side self-absorption and the p-side self-absorption especially by the p-side emission due to the device structure. .

Further, as described above, the Al composition ratio of the n-type contact layer 3 is specified, preferably, the impurity concentration is specified in addition to the Al composition ratio. A first p-type contact layer 7a having a high impurity concentration and a low Al composition ratio and a low p-type impurity concentration A
Combining the formation with the second p-type contact layer 7b having a high l composition ratio can more favorably prevent self-absorption without causing a decrease in ohmic contact, and is more preferable in terms of improving light emission output.

Further, other layers constituting the device will be described below. [Substrate 1] In the present invention, as the substrate 1, sapphire having a sapphire C-plane, an R-plane or an A-plane as a main surface, an insulating substrate such as spinel (MgA1 ₂ O ₄ ), SiC ( 6H, 4H, 3C), Si, Zn
A semiconductor substrate such as O, GaAs, or GaN can be used.

[Buffer Layer 2] In the present invention, as the buffer layer 2, Ga _h Al ₁ -hN (where h is 0 <h ≦ 1)
Range. ), The crystallinity of the composition is more remarkably improved as the composition of Al is smaller, and the buffer layer 2 is more preferably made of GaN. The thickness of the buffer layer 2 is 0.002 to 0.5
μm, preferably in the range of 0.005 to 0.2 μm, more preferably 0.01 to 0.02 μm. When the thickness of the buffer layer 2 is in the above range, the crystal morphology of the nitride semiconductor becomes good, and the crystallinity of the nitride semiconductor grown on the buffer layer 2 is improved. The growth temperature of the buffer layer 2 is 200 to 900 ° C., preferably 40 ° C.
Adjust to the range of 0 to 800 ° C. When the growth temperature is in the above range, a favorable polycrystal is formed, and this polycrystal is preferable because the crystallinity of the nitride semiconductor grown on the buffer layer 2 as a seed crystal can be improved. The buffer layer 2 grown at such a low temperature may be omitted depending on the type of the substrate, the growth method, and the like.

[N-type contact layer 3] A nitride semiconductor containing AlGaN containing the above-mentioned n-type impurity.

[N-type cladding layer 4]
The type cladding layer 4 has a composition that is larger than the band gap energy of the active layer 5 and is not particularly limited as long as carriers can be confined in the active layer 5, but a preferable composition is Al _e Ga _{1 -e.} N (0 <e <0.
3, preferably 0.1 <e <0.2). It is preferable that the n-type cladding layer is made of such AlGaN in terms of confining carriers in the active layer. n
The thickness of the mold cladding layer is not particularly limited, but is preferably 0.01 to 0.1 μm, more preferably 0.0 to 0.1 μm.
3 to 0.06 μm. The n-type impurity concentration of the n-type cladding layer is not particularly limited, but is preferably 1 × 10 ¹⁷ to
1 × 10 ²⁰ / cm ³ , more preferably 1 × 10 ¹⁸
１1 × 10 ¹⁹ / cm ³ . It is preferable that the impurity concentration be in this range in terms of resistivity and crystallinity.

The n-type cladding layer may be a multilayer film (including a superlattice structure) in addition to the single layer described above. In the case of a multilayer film layer, a multilayer film layer composed of the above Al _e Ga _1-e N and a nitride semiconductor layer having a smaller band gap energy may be used. , In _k Ga _1-k N
(0 ≦ k <1), Al _j Ga _1-j N (0 ≦ j <1, e>
j). The thickness of each layer forming the multilayer film layer is
Although not particularly limited, in the case of a superlattice structure, the thickness of one layer is 100 angstrom or less, preferably 70 angstrom or less, more preferably 10 to 40 angstrom. It can be a layer composed of a composition. In the case where the n-type cladding layer is a multilayer film layer including a layer having a large band gap energy and a layer having a small band gap energy, at least one of the layer having a large band gap energy and the layer having a small band gap energy is doped with an n-type impurity. May be. When doping both the layer having a large band gap energy and the layer having a small band gap energy, the doping amount may be the same or different.

[Active Layer 5] In the present invention, the active layer 5 includes a nitride semiconductor having a composition such that the emission peak wavelength is 370 nm or less. Preferably In _g G
a _1-g N (0 ≦ g <0.1) nitride semiconductor; The In composition ratio of the active layer decreases as the emission peak wavelength becomes shorter, but the In composition ratio becomes almost zero. The thickness of the active layer is not particularly limited, but may be a thickness at which a quantum effect can be obtained, for example, preferably 0.001 to 0.01 μm, and more preferably 0.003 to 0.007 μm. is there. It is preferable that the film thickness is in the above range in terms of light emission output.
In addition to the single quantum well structure as described above, the active layer has a multiplex structure including the above-mentioned In _g Ga _{1 -g} N as a well layer and a barrier layer having a composition having a band gap energy larger than that of the well layer. It may be a quantum well structure. The active layer may be doped with impurities.

Adjustment of the In composition ratio of the active layer is not particularly limited as long as the In composition ratio at which the emission peak wavelength becomes 370 nm or less is used. Specific values include, for example, calculation of the following theoretical values. A value obtained from the equation can be given as an approximate value. However, the wavelength obtained by actually emitting light has a quantum level having a quantum well structure, so that the energy of the wavelength (Eλ) is larger than the band gap energy (Eg) of InGaN. There is a tendency to shift to a shorter wavelength side than the required emission wavelength.

[Calculation formula of theoretical value] Eg = (1-χ) 3.40 + 1.95χ-Bχ (1-
χ) wavelength (nm) = 1240 / Eg Eg: band gap energy of InGaN well layer χ: composition ratio of In 3.40 (eV): band gap energy of GaN 1.95 (eV): band gap energy of InN B : Indicates a bowing parameter, which is 1 to 6 eV. The variation of the Boeing parameter like this is
In recent studies, from SIMS analysis and the like, it has been conventionally assumed that the crystal has no distortion, but it is set to 1 eV. It is becoming clear that

Although there is a slight difference between the oscillation wavelength considered from the specific In composition ratio obtained from the SIMS analysis of the well layer and the like as described above and the oscillation wavelength when actually oscillated, The oscillation wavelength is adjusted to be a desired wavelength.

[P-type cladding layer 6]
The type cladding layer 6, a larger composition than the band gap energy of the active layer 5 is not particularly limited as long as it can confine carriers in the active layer 5, preferably, Al _f Ga _1-f N (0 <f <0.4, preferably 0.15 <f <0.3).
When the p-type cladding layer is made of such AlGaN,
This is preferable in terms of confining carriers in the active layer. The thickness of the p-type cladding layer is not particularly limited, but is preferably 0.01 to 0.15 μm, more preferably 0.01 to 0.15 μm.
4 to 0.08 μm. The p-type impurity concentration of the p-type cladding layer is not particularly limited, but is preferably 1 × 10 ¹⁸ to
1 × 10 ²¹ / cm ³ , more preferably 1 × 10 ¹⁹
５5 × 10 ²⁰ / cm ³ . It is preferable that the p-type impurity concentration is within the above range, since the bulk resistance is reduced without lowering the crystallinity.

The p-type cladding layer may be a multilayer layer (including a superlattice structure) in addition to the single layer as described above. For multilayer film, the above Al _f Ga _1-f N, but may be a multilayer film made of it than the band gap energy smaller nitride semiconductor layer, for example, as a small layer bandgap energy As in the case of the n-type cladding layer, In _k Ga _{1 -kN} (0 ≦ k <1), Al _j
Ga _1-j N (0 ≦ j <1, f> j). The thickness of each layer forming the multilayer film layer is not particularly limited, but in the case of a superlattice structure, the thickness of each layer is 100 Å or less, preferably 70 Å or less, more preferably 10 to 40 Å. In the case of a single layer that does not form a structure, it can be a layer having the above composition. Further, when the p-type cladding layer is a multilayer film layer including a layer having a large band gap energy and a layer having a small band gap energy, at least one of the layer having a large band gap energy and the layer having a small band gap energy is doped with a p-type impurity. May be. When doping both the layer having a large band gap energy and the layer having a small band gap energy, the doping amount may be the same or different.

[P-type contact layer 7] It is a nitride semiconductor containing AlGaN containing the above-mentioned p-type impurity.

In the present invention, various types of p-electrode and n-electrode can be used, and are appropriately selected from known electrode materials and the like. Specific examples of the electrode include those described in Examples below. Although the present invention has been described with reference to FIG. 1 as an embodiment of the element structure, the emission peak wavelength is 370 nm or less, and the specific n-type contact layer and p-type contact layer of the present invention as described above are used. If this is the case, the effect of the present invention can be obtained. In addition to FIG. 1, other layers may be formed in order to improve element characteristics such as electrostatic withstand voltage, forward voltage, and life characteristics.

In the device of the present invention, an annealing process is performed in order to make the p-side layer p-type and have a low resistance. The annealing process is described in Japanese Patent No. 2540791.
As described above, after growing a gallium nitride-based compound semiconductor doped with a p-type impurity by a vapor phase growth method, the gallium nitride-based compound semiconductor is heated at 400 ° C. in an atmosphere substantially containing no hydrogen.
There is a method in which a heat treatment is performed at the above temperature to generate hydrogen from a gallium nitride-based compound semiconductor doped with a p-type impurity to make the semiconductor p-type.

[0037]

The present invention will be described below in more detail with reference to examples which are embodiments of the present invention. However, the present invention is not limited to this.

Example 1 In Example 1, the nitride semiconductor device shown in FIG. 1 was manufactured. (Substrate 1) The surface of the substrate 1 made of sapphire (C plane) is cleaned at 1050 ° C. in a hydrogen atmosphere in a reaction vessel.

(Buffer Layer 2) Subsequently, in a hydrogen atmosphere,
At 510 ° C., a buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of about 200 angstroms using ammonia and TMG (trimethylgallium).

(N-type contact layer 3) Next, at 1050 ° C., using TMG, TMA (trimethylaluminum), ammonia, and silane (SiH ₄ ), Si is formed at 5 × 10 ¹⁸ / c.
An n-type contact layer 3 made of m ³ -doped n-type Al _0.04 Ga _0.96 N is grown to a thickness of 4 μm.

(N-type cladding layer 4) Next, at 1050 ° C., T
Using MG, TMA, ammonia, silane, Si is 5 ×
An n-type cladding layer 4 made of n-type Al _0.18 Ga _0.82 N doped with 10 ¹⁷ / cm ³ is formed to a thickness of 400 Å.

(Active Layer 5) Next, at 700 ° C. in a nitrogen atmosphere.
Undoped In using TMI, TMG and ammonia
An active layer made of GaN is grown to a thickness of 55 Å. The In composition ratio is so small (almost zero) that it cannot be measured.

(P-type cladding layer 6) Next, in a hydrogen atmosphere,
TMG, TMA, ammonia, Cp ₂ Mg at 1050 ° C
Using (cyclopentadienyl magnesium), a p-type cladding layer 6 made of Al _0.2 Ga _0.8 N doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 600 Å.

(P-type contact layer 7) Subsequently, on the p-type cladding layer 6, TMG, TMA, ammonia, Cp ₂ M
g of Al doped with 1 × 10 ¹⁹ / cm ^{3 of} Mg
_A second p-type contact layer 7b made of _0.04 Ga _0.96 N is grown to a thickness of 0.1 μm, and then the gas flow rate is adjusted to make Al _0.01 G doped with 2 × 10 ²¹ / cm ³ Mg.
The second p-type contact layer 7b made of a _0.99 N
It is grown to a thickness of 2 μm.

After the growth is completed, the wafer is annealed at 700 ° C. in a reaction vessel in a nitrogen atmosphere.
After further reducing the resistance of the mold layer, the wafer is taken out of the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer 7, and the p-type contact layer is formed by an RIE (reactive ion etching) apparatus. Etching from the side,
As shown in FIG. 1, the surface of the n-type contact layer 3 is exposed.

After the etching, almost all of the first p-type contact layer 7a of the uppermost p-type contact layer 7 is formed of a light-transmitting p-type layer containing Ni and Au having a thickness of 200 angstroms.
An electrode 8 and a p pad electrode 10 made of Au for bonding are formed on the p electrode 8 with a thickness of 0.2 μm. On the other hand, an n-electrode 9 containing W and Al is formed on the surface of the n-type contact layer 3 exposed by etching. Finally, after an insulating film made of SiO ₂ is formed to protect the surface of the p-electrode 8, the wafer is separated by scribing to obtain LED elements of 350 μm square.

This LED element has an emission peak wavelength of 370 nm at a forward voltage of 20 mA, and Vf is 3.
8V, the output is 2.0 mW. The light extraction efficiency of the LED of the first embodiment is such that the conventional n-type and p-type contact layers
It is almost 2.5 times as large as those not including l. As described above, since the ohmic contact is improved by the above-described element structure, the same Vf as that of the related art can be maintained, and the self-absorption can be prevented, so that the emission output can be improved.

[0048]

According to the present invention, as described above, the n-type contact layer and the p-type contact layer can be formed by changing the Al composition ratio and the impurity concentration.
Further, by forming the p-type contact layer from two layers, self-absorption can be effectively prevented without deteriorating ohmic contact, light extraction efficiency can be improved, and a nitride semiconductor device having a good light output of 370 nm or less can be provided. can do. Further, the present invention, by the combination of Mg concentration of the n-type and p-type contact layers and a specific cladding layer,
In addition to good ohmic contact and prevention of self-absorption, prevention of cracks and the like becomes good, and a better light emission output can be obtained.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 3 ... n-type contact layer 4 ... n-type cladding layer 5 ... Active layer 6 ... p-type cladding layer 7 ... p-type contact layer 7b ... 2nd p-type contact layer 7a ... 1st p-type contact layer 8 ... p electrode 9 ... n electrode 10 ... pad electrode

Claims (6)

[Claims] 1. A nitride semiconductor device having at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on a substrate, wherein the active layer has an emission peak wavelength of 370 nm or less. A p-type nitride semiconductor layer,
A p-type contact layer in contact with the p-electrode has an Al _a Ga _1-a N (0
≦ a <0.05), and a first p-type contact layer on the active layer side of the first p-type contact layer.
A p-type impurity in a lower concentration than the first p-type contact layer in contact with the p-type contact layer;
Al _b Ga ₁ -bN (0 <b <
Is formed and a second p-type contact layer comprising a 0.1) becomes, the further as the n-type nitride semiconductor layer, n-type contact layer in contact with the n electrode, Al _d Ga _1-d N (0 <d <0.
A nitride semiconductor light-emitting diode, comprising: 1). 2. The method according to claim 1, wherein the first p-type contact layer in contact with the p-electrode comprises a p-type impurity of 1 × 10 ¹⁹ to 1 × 10 ²² / cm ^3.
The nitride semiconductor light-emitting diode according to claim 1, wherein the light-emitting diode is contained. 3. The nitride semiconductor light-emitting diode according to claim 1, wherein the second p-type contact layer contains a p-type impurity at 1 × 10 ²⁰ / cm ³ or less. 4. The first p-type contact layer in the p-type contact layer.
The thickness of the p-type contact layer is 100 to 500 Å, and the thickness of the second p-type contact layer is
The nitride semiconductor light emitting diode according to claim 1, wherein the thickness is 400 to 2000 Å. 5. The nitride semiconductor light emitting diode according to claim 4, wherein said n-type contact layer contains an n-type impurity at 1 × 10 ¹⁷ to 1 × 10 ¹⁹ / cm ³ . 6. A first nitride semiconductor layer comprising Al _e Ga _{1 -eN} (0 <e <0.3) between the active layer and the n-type contact layer, further comprising: , Al _f Ga _{1 -fN} (0 <f <0...) Between the active layer and the p-type contact layer.
2. The nitride semiconductor light-emitting diode according to claim 1, further comprising a second nitride semiconductor layer containing (4).