JPH08330629A - Light-emitting nitride semiconductor element - Google Patents

Abstract

PURPOSE: To obtain a light-emitting nitride semiconductor element which lowers a Vf (a forward voltage) by a method wherein a p-type layer forming a positive electrode is constituted of a heavily acceptor-doped first p-type layer and a lightly doped second p-type layer. CONSTITUTION: A contact layer is constituted of a first p-type contact layer 71 in which a layer coming into contact with a positive electrode 9 is formed as a heavily acceptor-doped first nitride semiconductor layer and a second p-type contact layer 72 as a second nitride semiconductor layer acceptor-doped more lightly than the first p-type contact layer. The acceptor concentration of the first heavily doped p-type contact layer is adjusted to 1×10<17> to 5×10<21> /cm<3> . The acceptor concentration of the second lightly doped p-type contact layer 2 is adjusted to a range of 2×10<15> to 5×10<20> /cm<3> . The contact layer 71, 72 form the positive electrode 9, and they are layers which can form desirable ohmic contacts with the positive electrode 9. The closer they are perfect ohmic contacts, the more the Vf of a light-emitting element can be lowered.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a light emitting diode (LE
D), nitride semiconductors (In _a Al _b Ga _1-ab N, 0 ≦ a, 0 ≦ b, a + b used for laser diode (LD), etc.
<1) The present invention relates to a light emitting device having a double hetero structure having an active layer between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer.

[0002]

2. Description of the Related Art Nitride semiconductors (In _a Al _b Ga) have been used as materials for light emitting devices such as LEDs and LDs that emit ultraviolet to red light.
_1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1) are known.
Using this semiconductor material, we announced a blue LED with a luminous intensity of 1 cd in November 1993, a blue-green LED with a luminous intensity of 2 cd in April 1994, and a blue LED with a luminous intensity of 2 cd in October 1994. Announced. All of these LEDs have been commercialized and are now in practical use for displays, road signals, etc.

FIG. 2 shows a conventional blue color composed of a nitride semiconductor,
The structure of the light emitting chip of a blue-green LED is shown. Basically,
On the substrate 21, a buffer layer 22 made of GaN, an n-type contact layer 23 made of n-type GaN, and an n-type AlGa
An n-type clad layer 24 made of N, an active layer 25 made of n-type InGaN, a p-type clad layer 26 made of p-type AlGaN, and a p-type contact layer 27 made of p-type GaN.
It has a double hetero structure in which and are sequentially stacked. The n-type InGaN of the active layer 25 is doped with donor impurities such as Si and Ge and / or acceptor impurities such as Zn and Mg, and the emission wavelength of the LED element changes the In composition ratio of InGaN of the active layer. It is possible to change from ultraviolet to red by changing the kind of impurities to be doped into the active layer. Currently, an LED having an emission wavelength of 510 nm or less, in which an active layer is simultaneously doped with a donor impurity and an acceptor impurity, has been put into practical use.

[0004]

The conventional blue LED has a forward current (If) of 20 mA and a forward voltage (Vf) of 3.
The light emission output is 6 V to 3.8 V, and the light emission output is close to 3 mW, and the light emission output is 20 times or more that of the blue LED made of SiC. The forward voltage is low because the pn junction is formed, and the light emission output is high because the double hetero structure is realized. As described above, the LEDs currently put into practical use have extremely high performance, but light emitting elements such as LEDs and LDs with higher performance are required. For example, the Vf of the LED is 3.6 V or more as described above.
Although it has achieved a low value of 3.8 V, it is necessary to further reduce Vf in order to realize a light emitting element having a small electrode width and a small electrode area such as an LD.

Therefore, the present invention has been made in view of such circumstances, and an object thereof is to further improve the performance of a light emitting device made of a nitride semiconductor having a double hetero structure. , Specifically, V of the light emitting element
It is to provide an element having excellent luminous efficiency by further reducing f.

[0006]

The light emitting device of the present invention has
A nitride semiconductor light emitting device having an active layer for emitting light between a p-type nitride semiconductor layer and a p-type nitride semiconductor layer, wherein a positive electrode is formed on the surface of the p-type nitride semiconductor layer. The object semiconductor layer is a first p-type nitride semiconductor layer having a high acceptor impurity concentration in order from the side in contact with the positive electrode, and a second p-type nitride having a lower acceptor impurity concentration than the first p-type nitride semiconductor layer. And a semiconductor layer.

Further, in the above light emitting device, the film thickness of the first p-type nitride semiconductor is 0.1 μm or less, more preferably 500 angstroms or less, and most preferably 200.
Adjust to less than Angstrom. If it is thicker than 0.1 μm, crystal defects due to impurities increase in the crystal itself, and Vf tends to increase.

[0008]

A technique for making the p layer a high carrier concentration p + type and a low carrier concentration p type is described in JP-A-6-151964, JP-A-6-151965, JP-A-6-151966 and the like. . The light emitting elements disclosed in these publications emit light by a homojunction of GaN. Therefore, with the pn junction interface as a reference, n is separated in the direction away from this junction interface.
The n-type GaN layer is a low carrier concentration n-type and a high carrier concentration n + type, and the p-type GaN is a low carrier concentration p-type and a high carrier concentration p + -type. By combining the n-layer and the p-layer having these two-stage carrier concentration, the long-life and light-emission luminance of the light-emitting element are improved.

On the other hand, the light emitting device of the present invention is different from the above publication in that the p-type layer of the light emitting device having the double hetero structure is a second p-type layer having a low acceptor impurity concentration and a first p-type layer having a high acceptor impurity concentration. Is a p-type layer. The light emitting element having the double hetero structure has a light emission output 10 times or more higher than that of the homojunction light emitting element. Therefore, even if the p-type layer is a combination of p + -type and p-type as in the above publication, the output is hardly increased. Rather, the present invention differs from the conventional art in that Vf of the double hetero structure is lowered rather than the light emission output to improve the light emission efficiency. Regarding the acceptor impurities, the carrier concentration is generally approximately proportional to the concentration of the acceptor impurities. However, in the case of a nitride semiconductor, after the semiconductor layer is doped with the acceptor impurities, annealing is performed at 400 ° C. or higher to obtain a complete p-type impurity. Acts as a mold. For this reason, the hole carrier concentration often changes depending on the annealing state, the annealing temperature, etc., and it is difficult to accurately measure the carrier concentration when the device structure is adopted. Therefore, in the present invention, the light emitting device is characterized by the acceptor impurity concentration. I am attaching.

Next, the light emitting device of the present invention has a conventional p
Instead of using the −n junction interface as a reference, the contact surface of the positive electrode is used as a reference, and the surface in contact with this positive electrode is used as the first p-type layer having a high impurity concentration and is in contact with the first p-type layer. The difference is that the second p-type layer has a low impurity concentration. By configuring the p layer with reference to the layer in contact with the positive electrode, V
f can be reduced.

Further, the light emitting device disclosed in the above publication,
The most different point from the light emitting device of the present invention is the film thickness of the p + layer. That is, in the above publication, the light emission output of the light emitting device is reduced unless the film thickness of the p + type semiconductor layer having a high carrier concentration is 0.2 μm or more. When the layer thickness is 0.2 μm or more, Vf
Will be higher. This is due to deterioration of crystallinity due to impurity doping. On the contrary, in the light emitting device of the present invention, the film thickness of the first p-type layer having a high impurity concentration is preferably 0.1 μm or less. By setting the thickness to 0.1 μm or less, Vf of the light emitting element can be effectively reduced.

[0012]

【Example】

Example 1 The light emitting device of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the present invention. This light emitting device includes a buffer layer 2, an n-type contact layer 3, an n-type cladding layer 4, an active layer 5, a p-type cladding layer 6, a second p-type contact layer 72 having a low acceptor impurity concentration, and an acceptor on a substrate 1. This shows a structure in which the first p-type contact layer 71 having a high impurity concentration is sequentially stacked. Further, the positive electrode 9 is formed on the first p-type contact layer 71, and the negative electrode 8 is formed on the n-type contact layer 3.

The substrate 1 includes sapphire (including A-plane, C-plane, R-plane), SiC (including 6H and 4H), ZnO,
A substrate having a lattice mismatch with a nitride semiconductor such as Si or GaAs, or a substrate having a lattice constant close to that of a nitride semiconductor made of an oxide single crystal such as NGO (neodymium gallium oxide) can be used.

The buffer layer 2 is composed of GaN, AlN, GaAl.
It is preferable to grow N or the like in a film thickness of 50 angstrom to 0.1 μm, for example, and it can be formed by growing at a low temperature of 400 ° C. to 600 ° C. according to the MOVPE method. The buffer layer 2 is provided to alleviate the lattice mismatch between the substrate 1 and the nitride semiconductor.
The buffer layer may not be formed when a substrate having a lattice constant close to that of a nitride semiconductor such as nO or a substrate lattice-matched to a nitride semiconductor is used.

The n-type contact layer 3 is a layer for forming the negative electrode 8. It is preferable to grow GaN, AlGaN, InAlGaN or the like to have a film thickness of, for example, 1 μm to 10 μm. A favorable ohmic contact with the material can be obtained. As the material of the negative electrode 8, for example, Ti and Al, Ti and Au, etc. can be preferably used.

The n-type cladding layer 4 is composed of GaN, AlGaN,
InAlGaN or the like is, for example, 500 Å
It is preferable to grow the film with a thickness of 0.5 μm, and by selecting GaN or AlGaN among them, a layer with good crystallinity can be obtained. It is also possible to omit either the n-type cladding layer 4 or the n-type contact layer 3. If either is omitted, the remaining layer acts as an n-type cladding layer and an n-type contact layer.

The active layer 5 is made of InGaN, InAlGaN, A whose band gap energy is smaller than that of the cladding layer.
Any nitride semiconductor such as lGaN may be used, and in particular, InGaN in which the composition ratio of indium is appropriately changed according to a desired band gap is preferable. Further, the active layer 5 may have a multi-quantum well structure in which thin films are laminated by combining InGaN / GaN, InGaN / InGaN (having different compositions), for example. In the active layer having either a single quantum well structure or a multiple quantum well structure, the active layer may be either n-type or p-type. Luminescence or quantum well level luminescence is obtained, and LED
It is particularly preferable for realizing a device and an LD device. When the active layer has a single quantum well (SQW) structure or a multi-quantum well (MQW: multiquantum well) structure, a light emitting device having a very high output can be obtained. SQ
W and MQW refer to the structure of the active layer in which light emission between quantum levels by non-doped InGaN is obtained, and for example, SQW.
Then, the active layer is composed of a single composition of In _X Ga _1-X N (0 ≦ X <1)
By making the film thickness of In _X Ga _1-X N 100 angstroms or less, more preferably 70 angstroms or less, strong light emission between quantum levels can be obtained. MQW is In _X Ga _{1 -X} N with different composition ratios.
A multilayer film is formed by laminating a plurality of thin films (including X = 0 and X = 1 in this case). Thus, by making the active layer SQW and MQW, light emission between quantum levels is about 365 nm to 660.
Emission up to nm is obtained. As described above, the thickness of the quantum well layer is preferably 70 Å or less. In the multiple quantum well structure, it is desirable that the well layer is made of In _X Ga _{1 -X} N and the barrier layer is also made of In _Y Ga _{1 -Y} N (Y <X, including Y = 0 in this case). Particularly preferably, when the well layer and the barrier layer are formed of InGaN, they can be grown at the same temperature, so that an active layer having good crystallinity can be obtained. When the thickness of the barrier layer is 150 angstroms or less, more preferably 120 angstroms or less, a high-power light emitting device can be obtained. Further, the active layer 5 may be doped with a donor impurity and / or an acceptor impurity. If the crystallinity of the impurity-doped active layer is the same as that of the non-doped one, doping with the donor impurity can further increase the interband emission intensity as compared with the non-doped one. Doping with an acceptor impurity can bring the peak wavelength to a low energy side of about 0.5 eV lower than the peak wavelength of band-to-band emission, but the full width at half maximum becomes wider.
When the acceptor impurity and the donor impurity are doped at the same time, the emission intensity of the active layer doped with only the acceptor impurity can be further increased. Particularly when realizing an active layer doped with an acceptor impurity, it is preferable that the conductivity type of the active layer be n-type by simultaneously doping with a donor impurity such as Si. The active layer 5 can be grown to have a film thickness of, for example, several angstroms to 0.5 μm. However, when the active layer has a single quantum well structure or a multiple quantum well structure to reduce the thickness of the nitride semiconductor layer forming the active layer, the In layer between the n-type cladding layer 4 and the active layer 5 is
It is preferable to form the second n-type cladding layer 40 made of an n-type nitride semiconductor containing

The p-type cladding layer 6 is composed of GaN, AlGaN,
InAlGaN or the like is, for example, 500 Å
It is preferable to grow the film with a thickness of 0.5 μm, and by selecting GaN or AlGaN among them, a layer with good crystallinity can be obtained. The p-type clad layer 6 can be omitted.

Next, the contact layer 7 which is a feature of the present invention.
1, 72 will be described. The contact layers 71, 72
Is a layer that forms the positive electrode 9 and obtains a preferable ohmic contact with the positive electrode 9. The closer to a perfect ohmic contact, the lower the Vf of the light emitting element can be. Therefore, in this contact layer, the layer in contact with the positive electrode 9 is the first p-type contact layer 71 which is the first nitride semiconductor layer having a high acceptor impurity concentration, and the acceptor impurity is higher than that of the first p-type contact layer. And a second p-type contact layer 72 which is a second nitride semiconductor having a low concentration.

The first p-type contact layer 71 and the second p-type contact layer 72 are preferably formed of a nitride semiconductor having the same composition, for example, GaN, AlGaN, I.
It is possible to grow nAlGaN or the like. By selecting GaN among them, preferable ohmic contact with the material of the positive electrode 9 can be obtained.

The high-concentration first p-type contact layer 71 has an acceptor impurity concentration of 1 × 10 ^{17 to} 5 × 10 ²¹ / cm ^3.
It is desirable to adjust to. If it is lower than 1 × 10 ¹⁷ / cm ³ , it is difficult to obtain ohmic contact with the electrode.
When it is higher than 10 ²¹ / cm ^3, the crystallinity of the nitride semiconductor is deteriorated due to impurities, and Vf tends to be high.

On the other hand, a low concentration second p-type contact layer 7
The acceptor impurity concentration of 2 is 2 × 10 ^{15 to} 5 × 10 ²⁰
It is desirable to adjust to the range of / cm ³ . 2 x 10 ¹⁵ / c
If it is lower than m ³ , the resistance as p-type becomes high, so Vf
Tends to be higher. When it is higher than 5 × 10 ²⁰ / cm ^3, it is difficult to balance with the high-concentration first p-type contact layer 71, and there is a tendency that improvement of Vf cannot be expected so much.

As described above, the hole carrier concentration of the contact layers 71 and 72 changes the concentration of the acceptor impurities doped into the nitride semiconductor, or the contact layers 71 and 72 doped with the acceptor impurities.
Can be adjusted by annealing at 400 ° C. or higher, but it is difficult to measure an accurate value. Approximate value is 400 at the acceptor impurity concentration.
By performing the annealing at a temperature of not less than ° C, for example, the first p-type contact layer 71 having a hole carrier concentration of about 1 x 10 ^{16 to} 5 x 10 ¹⁹ / cm ³ is obtained, and the hole carrier concentration of about 1 x 10 ¹⁵ to 1 is obtained. A second p-type contact layer 72 of × 10 ¹⁹ / cm ³ is obtained.

A metal containing Ni and Au can be used as the material of the positive electrode 9 that can obtain a preferable ohmic contact with the first p-type contact layer 71. Ni and Au
A positive electrode containing a can obtain a preferable ohmic contact with p-type GaN.

The light emitting device of the present invention is, for example, MOVPE (metal organic chemical vapor deposition), MBE (molecular beam vapor deposition), H
In _a Al _b Ga _{1 -ab} N (0 ≦ a, 0 ≦ is formed on the substrate by using a vapor phase growth method such as DVPE (hydride vapor phase growth method).
It is obtained by stacking b, a + b ≦ 1) with conductivity types such as n-type and p-type. Although the n-type nitride semiconductor can be obtained in a non-doped state, it can be obtained by introducing a donor impurity such as Si, Ge, and S into the semiconductor layer during crystal growth.

On the other hand, the p-type nitride semiconductor layer is made of Mg, Z
Although it can be obtained by introducing acceptor impurities such as n, Cd, Ca, Be, and C into the semiconductor layer during crystal growth, as described above, annealing is performed at 400 ° C. or higher after the introduction of acceptor impurities. Thereby, a more preferable p-type is obtained.

Next, the light emitting device of FIG. 1 will be specifically described. The following example shows a growth method by the MOVPE method.

First, TMG (trimethylgallium) and N
Sapphire substrate 1 set in a reaction vessel using H ₃
Of the GaN buffer layer 2 at 500 ° C. on the C surface of
It is grown to a film thickness of 0 angstrom.

Next, the temperature is raised to 1050 ° C. and TMG,
Si-doped n-type GaN using silane gas in addition to NH _3.
The n-type contact layer 23 is made to have a thickness of 4 μm.

Subsequently, TMA (trimethylaluminum) was added to the source gas, and the n-type cladding layer 4 made of Si-doped n-type Al0.3Ga0.7N layer was also formed at 0.150 ° C. to 0.1%.
Grow with a film thickness of μm.

Next, the temperature is lowered to 800 ° C. and TMG, TM
I (trimethylindium), NH ₃, Silane gas, D
Si + Zn-doped n-type using EZ (diethyl zinc)
The active layer 5 made of In0.05Ga0.95N has a thickness of 0.1 μm.
Grow thick.

Next, the temperature is raised to 1050 ° C. and TMG, T
A p-type clad layer 6 made of Mg-doped p-type Al0.3Ga0.7N is grown to a thickness of 0.1 μm using MA, NH ₃ , and Cp2Mg (cyclopentadienylmagnesium).

Next, at 1050 ° C., TMG, NH ₃ , Cp2M
Using g, a second p-type contact layer 72 made of Mg-doped p-type GaN is grown to a thickness of 0.5 μm. The Mg concentration of this second p-type contact layer was 1 × 10 ¹⁸ /
It was cm ^3.

Subsequently, the flow rate of Cp 2 Mg is increased at 1050 ° C. to grow the first p-type contact layer 71 made of Mg-doped p-type GaN with a film thickness of 200 Å. The Mg concentration of the first p-type contact layer 71 was 2 × 10 ¹⁹ / cm ³ .

After the reaction is completed, the temperature is lowered to room temperature, the wafer is taken out from the reaction container, and the wafer is annealed at 700 ° C. to further reduce the resistance of the p-type layer. Next, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer 7, and etching is performed until the surface of the n-type contact layer 3 is exposed. After etching, the negative electrode 8 made of Ti and Al is formed on the surface of the n-type contact layer 3, and the positive electrode 9 made of Ni and Au is formed on the surface of the first p-type contact layer 71. After the electrodes were formed, the wafer was separated into chips of 350 μm square to obtain LED elements. This LED element is If2
At 0 mA, Vf3.1 V, emission peak wavelength 450 nm,
Blue light emission with a half-value width of 70 nm was exhibited, and the emission output was 3 mW.

[Embodiment 2] A light emitting device was obtained in the same manner as in Embodiment 1 except that the thickness of the first p-type contact layer 71 was 500 angstroms.
In Vf3.2V, the light emission output was almost the same.

[Embodiment 3] A light emitting device was obtained in the same manner as in Embodiment 1 except that the thickness of the first p-type contact layer 71 was 0.1 μm.
f was 3.3 V and the light emission output was 2.9 mW.

[Embodiment 4] A light emitting device was obtained in the same manner as in Embodiment 1 except that the film thickness of the first p-type contact layer 71 was 0.3 μm. Vf at If 20 mA was obtained.
Was 3.7 V, and the emission output was 2.8 mW.

[Embodiment 5] In Embodiment 1, the second p
The Mg concentration of the mold contact layer 72 is 5 × 10¹⁷/cm ³When
Then, the Mg concentration of the first p-type contact layer 71 is set to 1 × 10.
¹⁹/cm³The LED element was obtained in the same manner except that
In fact, it showed almost the same characteristics as in Example 1.

[Embodiment 6] FIG. 3 is a schematic sectional view showing the structure of a light emitting device according to Embodiment 5. The difference between this light emitting device and the light emitting device of FIG. 1 is that n containing In is added as a new buffer layer between the n-type cladding layer 4 and the active layer 5.
The second n-type clad layer 40 made of a positive type nitride semiconductor is being formed. This second cladding layer 40
Is preferably formed to have a film thickness of 10 angstroms or more and 0.1 μm or less. Further, when the film thickness of the second n-type cladding layer 40 and the active layer 5 is 300 angstroms or more, the first n-type containing In is formed. The clad layer 40 and the active layer 5 containing In act as a buffer layer, and the n-type clad layer 4 and the p-type clad layer 6 can be grown with good crystallinity without cracks. Furthermore, this second n-type cladding layer 40
Growth of the active layer having a quantum structure in which no impurity is doped can be realized, and the full width at half maximum can be narrowed and high-power emission can be obtained. The second n-type cladding layer 4
0 may be GaN.

The second n-type cladding layer 40 acts as a buffer layer between the active layer 5 and the n-type cladding layer 4 containing Al and Ga. That is, since the second n-type cladding layer 40 containing In and Ga has a soft crystal property, the lattice constant mismatch between the n-type cladding layer 4 containing Al and Ga and the active layer 5 is caused. It has the function of absorbing the strain caused by the difference in thermal expansion coefficient. Therefore, even if the active layer has a single quantum well structure or a multiple quantum well structure and the thickness of the nitride semiconductor layer forming the active layer is reduced, cracks do not occur in the active layer 5 and the n-type cladding layer 4. The active layer is elastically deformed, and the crystal defects in the active layer are reduced.
That is, since the active layer has the quantum well structure, the crystallinity of the active layer is improved, and the light emission output is increased. further,
When the active layer has a quantum well structure, the light emission output increases due to the quantum effect and the exciton effect. In other words, in the conventional light emitting device, the thickness of the active layer is increased to, for example, 1000 angstroms or more to prevent cracks from forming in the cladding layer and the active layer. However, the active layer is always affected by the difference in coefficient of thermal expansion and strain due to lattice misalignment, and in conventional light emitting devices, the thickness of the active layer exceeds the elastically deformable critical film thickness. It cannot be deformed, many crystal defects are generated in the active layer, and the band-to-band emission does not emit much. This second n-type cladding layer 4
By forming 0, it is possible to dramatically improve the light emission output of the light emitting element when the active layer has a quantum structure.

Specifically, after growing the n-type cladding layer 4 in Example 1, the temperature was lowered to 800 ° C.
A second n-type cladding layer 40 made of Si-doped n-type In0.01Ga0.99N is grown to a thickness of 500 Å using G, TMI (trimethylindium), NH ₃ , and silane gas.

Then, using TMG, TMI, and NH ₃ , 80
An active layer 5 made of non-doped n-type In0.05Ga0.95N is grown to a thickness of 80 Å at 0 ° C. After that, when the p-type clad layer 6, the second p-type contact layer 72, and the first p-type contact layer 71 were grown into LED elements in the same manner as in Example 1, the LED elements were
Vf3.1V at f20mA, emission peak wavelength 400nm
Blue emission was exhibited, and the emission output was 12 mW. Further, the full width at half maximum of the emission spectrum was 20 nm, and the emission showed very good color purity.

[Embodiment 7] In Embodiment 6, the active layer 5 is used.
The composition of the non-doped In0.05Ga0.95N is 25 angstroms for the well layer and the non-doped In0.01Ga0.
A barrier layer of 99N is grown to a thickness of 50 Å. This operation was repeated 26 times, and finally well layers were laminated to grow the active layer 6 having a total thickness of about 2000 angstroms. After that, when an LED element was formed in the same manner as in Example 6, this LED element also showed Vf at If 20 mA.
It exhibited blue light emission with an emission peak wavelength of 400 nm at 3.1 V and an emission output of 12 mW. Further, the full width at half maximum of the emission spectrum was 20 nm, and the emission showed very good color purity.

[0045]

As described above, in the light emitting device of the present invention, in the light emitting device having the double hetero structure, the p-type layer forming the positive electrode is the first p-type layer having a high acceptor impurity concentration and the low impurity content. By setting the concentration of the second p-type layer, V
Since f can be reduced, the luminous efficiency is improved.
Therefore, when a large display using a large amount of LEDs, an outdoor advertising board, etc. are realized, a device with low power consumption can be realized, and its industrial utility value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the invention.

FIG. 2 is a schematic cross-sectional view showing the structure of a conventional light emitting element.

FIG. 3 is a schematic cross-sectional view showing the structure of a light emitting device according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... Substrate 2 ... Buffer layer 3 ... N-type contact layer 4 ... N-type clad layer 5 ... Active layer 6 ... P-type clad layer 72 ...・ ・ Second p-type contact layer 71 ・ ・ ・ ・ First p-type contact layer 8 ・ ・ ・ ・ Negative electrode 9 ・ ・ ・ ・ Positive electrode

Claims (3)

[Claims] 1. A nitride semiconductor light emitting device having an active layer for emitting light between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer, and a positive electrode formed on the surface of the p-type nitride semiconductor layer. In the first p-type nitride semiconductor layer, the first p-type nitride semiconductor layer having a high acceptor impurity concentration in order from the side in contact with the positive electrode, and the first p-type nitride semiconductor layer having a lower acceptor impurity concentration than the first p-type nitride semiconductor layer. And a second p-type nitride semiconductor layer. 2. The nitride semiconductor light emitting device according to claim 1, wherein the film thickness of the first p-type nitride semiconductor layer is 0.1 μm or less. 3. The nitride semiconductor light emitting device according to claim 1, wherein the positive electrode contains nickel and gold.