JP2000188423A - Formation of nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly enhance the output of a nitride semiconductor device by forming on a second nitride semiconductor layer a third nitride semiconductor layer containing more p-type impurities than those in a first nitride semiconductor layer. SOLUTION: An LED device is structured by laminating on a sapphire substrate 1 a buffer layer 2 of GaN, an n-contact layer 3 of Si-doped GaN, an active layer 4 of InGaN of single quantum well structure, 30 Å in film thickness, a first p-side nitride semiconductor layer 5 of Mg-doped AlGaN, a second p-side nitride semiconductor layer 6 of GaN, doped with less Mg than in the first p-side nitride semiconductor layer 5, and a third p-side nitride semiconductor layer 7 of GaN, doped with more Mg than in the first p-side nitride semiconductor layer 5. A p-electrode 8 of a translucent metallic thin film is formed on the substantially entire surface of the third p-side nitride semiconductor layer 7, and a pad electrode 9 for bonding is formed at a coner of the p-electrode 8 with an n-electrode 10 formed on the surface of the n-side contact layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor (In _X Al _Y Ga _{1 -XYN} , 0 ≦ X,
The present invention relates to a method for forming an element comprising 0 ≦ Y and X + Y ≦ 1).

[0002]

2. Description of the Related Art A nitride semiconductor is used as a material for a high-brightness blue LED and a pure green LED by the present applicant.
It has just been put to practical use in ED displays and traffic signals. The LEDs used in these various devices are n
Between a p-type nitride semiconductor layer and a p-type nitride semiconductor layer, a single-quantum-well (SQW)
It has a double hetero structure in which an active layer made of GaN is sandwiched. Wavelengths such as blue and green are determined by the IGaN of the InGaN active layer.
It is determined by increasing or decreasing the n composition ratio. Blue LED
Is an emission wavelength of 450 nm and a half width of 20 n at 20 mA.
m, luminous intensity 2 cd, optical output 5 mW, external quantum efficiency 9.1%
It is. On the other hand, the green LED is also at 20 mA,
The emission wavelength is 525 nm, the half width is 30 nm, the luminous intensity is 6 cd, the optical output is 3 mW, and the external quantum efficiency is 6.3%.

[0003] The present applicant has recently used this material to
World's first laser oscillation at room temperature under lus current
First published {for example, Jpn.J.Appl.Phys.35 (1996) L7
4, Jpn.J.Appl.Phys.35 (1996) L217}. This laser element
Has an active layer with a multiple quantum well structure using InGaN.
Pulse width 2μs, pulse width
Under the condition of a cycle of 2 ms, the threshold current is 610 mA and the threshold current density is
8.7 kA / cm^Two, 410 nm oscillation. Improved
Laser element is also described in Appl.Phys.Lett. 69 (1996) 1477.
We announced. This laser device is a p-type nitride semiconductor
With a structure in which a ridge stripe is formed in part of the layer
Pulse width 1μs, pulse period 1ms, duty
-With a ratio of 0.1%, a threshold current of 187 mA and a threshold current density of 3
kA / cm ^Two, 410 nm oscillation. Further, the applicant
Announced for the first time continuous oscillation at room temperature. {Example
For example, Nikkei Electronics December 2, 1996 issue
, Appl.Phys.Lett.69 (1996) 3034, Appl.Phys.Lett.69
(1996) 4056 et al.], This laser device has a threshold
Value current density 3.6 kA / cm^Two, Threshold voltage 5.5V, 1.
At 5 mW output, it shows continuous oscillation for 27 hours.

[0004]

As described above, the light emitting device using the nitride semiconductor has already been put to practical use as an LED, but there are still insufficient points, and further improvement in the light emitting output is desired. In addition, LDs are currently under intensive research with a view to practical use, and it is desired not only to improve the output but also to extend the life. If the light emission output of a light emitting device such as an LED or LD can be improved, the light receiving efficiency of a light receiving device such as a solar cell or an optical sensor having a similar structure can be improved at the same time. Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for forming a nitride semiconductor device having a novel structure, and thereby to mainly provide a method for forming an LED or LD. The purpose is to improve the output.

[0005]

That is, the present invention can be achieved by the following constitutions. (1) an active layer forming step of forming an active layer including at least a nitride semiconductor layer, and a first nitride semiconductor layer forming step of forming a first nitride semiconductor layer containing a p-type impurity on the active layer Forming a second nitride semiconductor layer on the first nitride semiconductor layer, the second nitride semiconductor layer containing a smaller amount of p-type impurity than the p-type impurity concentration of the first nitride semiconductor layer; Forming a third nitride semiconductor layer on the second nitride semiconductor layer, the third nitride semiconductor layer containing a larger amount of p-type impurities than the p-type impurity concentration of the first nitride semiconductor layer A method for forming a nitride semiconductor device, comprising at least a semiconductor layer forming step. (2) The method for forming a nitride semiconductor device according to (1), wherein the p-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁷ or more and 1 × 10 ²⁰ or less. (3) The p-type impurity concentration of the second nitride semiconductor layer is less than 1 × 10 ^20.
Or the method for forming a nitride semiconductor device according to (2). (4) The p-type impurity concentration of the third nitride semiconductor layer is 1 × 10 ¹⁸ or more and 1 × 10 ²¹ or less, according to any one of the above (1) to (3). Of forming a nitride semiconductor device.

That is, according to the present invention, the p-type impurity concentration of a plurality of specific p-side nitride semiconductor layers stacked on the active layer is defined, and the plurality of p-side nitrides further defining the p-type impurity concentration are defined. By defining the stacking order of the semiconductor layers, LED, LD
This is a forming method capable of improving the output of the device. In the present invention, the active layer and the first nitride semiconductor layer do not have to be formed in contact with each other, and the first nitride semiconductor layer and the second nitride semiconductor layer are formed in contact with each other. The second nitride semiconductor layer and the third nitride semiconductor layer need not be formed in contact with each other.

[0007]

FIG. 1 is a schematic sectional view showing the structure of a nitride semiconductor device according to one embodiment of the present invention, and specifically shows the structure of an LED device. As the element structure, GaN is provided on a substrate 1 made of sapphire.
Buffer layer 2 made of Si-doped GaN, n-side contact layer 3 (also n-side clad layer), active layer 4 made of InGaN having a single quantum well structure having a thickness of 30 angstroms, and first layer made of Mg-doped AlGaN p-side nitride semiconductor layer 5, second p-side nitride semiconductor layer 6 made of GaN doped with a smaller amount of Mg than first p-side nitride semiconductor layer 5, Mg formed of first p-side nitride semiconductor A third p-side nitride semiconductor layer 7 made of GaN doped more than the layer 5 is laminated. A p-electrode 8 made of a light-transmitting metal thin film is formed on almost the entire surface of the third p-side nitride semiconductor layer 7, and a pad electrode 9 for bonding is formed at a corner of the entire electrode 8. I have. On the other hand, an n-electrode 10 is formed on the surface of the n-side contact layer 3 exposed by etching from the p-side nitride semiconductor layer side.

As described above, the device according to the present invention provides the second p-side nitride semiconductor layer whose p-side impurity concentration is to be defined to be smaller than the p-side impurity concentration of the first p-side nitride semiconductor layer. The light-emitting element output can be improved by forming the third p-side nitride semiconductor layer in which the p-side impurity concentration is largely specified in a specific stacking order. That is, a third p-side nitride semiconductor layer heavily doped with a p-type impurity acting as a contact layer and a position closer to the active layer than the third p-side nitride semiconductor layer are provided. The impurity is the first p
A second p-side nitride semiconductor layer doped less than the side nitride semiconductor layer, and a p-type impurity less than the third and more than the second at a position closer to the active layer than the second nitride semiconductor By providing the doped first p-side nitride semiconductor layer, the output of the entire device can be improved.

The active layer 4 has a single quantum well structure or a multiple quantum well structure including a nitride semiconductor layer containing at least In. The well layer has a thickness of 100 angstrom or less, more preferably 70 angstrom or less.
It is desirable to constitute in _{X Ga 1-X N (0} <X ≦ 1),
The barrier layer has a band gap energy higher than that of the well layer, _namely, In _Y Al _Z Ga _{1 -YZ} N (0 ≦ Y, 0 ≦ Z, Y + Z).
≦ 1) is desirably set to a film thickness of 200 angstroms or less, more preferably 150 angstroms or less.

The first p-side nitride semiconductor layer 5 only needs to be formed of a nitride semiconductor layer containing a p-type impurity, and may or may not particularly be in contact with the active layer. As the semiconductor, a nitride semiconductor having a band gap energy larger than that of the active layer is selected. For example, as described above, Al _x Ga ₁ -xN (0
≦ X ≦ 1) is preferably grown. The p-type impurity concentration doped in the first p-side nitride semiconductor layer 5 is 1 × 10 ¹⁷ /
cm ³ or more and 1 × 10 ²⁰ / cm ³ or less, preferably 1 × 10 ¹⁸
/ Cm ³ or more, more preferably 1 × 10 ¹⁹ / cm ³ . However, within this range, adjustment is made so that the number is larger than the second nitride semiconductor layer and smaller than the third nitride semiconductor layer. It is preferable that the p-type impurity concentration is within the above range for obtaining the effects of the present invention. As a p-type impurity that can be doped into the first p-type nitride semiconductor layer 5, for example, a group II element such as Mg, Zn, Cd, Ca, Be, or Sr is preferably doped. Further, the first nitride semiconductor layer may be a superlattice layer in which two types of nitride semiconductor layers having different compositions are stacked. When a superlattice layer is used, the thickness of the nitride semiconductor layer constituting the superlattice layer is 10
The film thickness is adjusted to 0 Å or less, more preferably 70 Å or less, and most preferably 50 Å or less. When the film thickness is in this range, it is preferable in terms of light emission output and forward voltage. In the present invention, when the first nitride semiconductor layer 5 is a superlattice layer, the crystallinity of the nitride semiconductor layer is improved, and the output is further improved. When forming a superlattice layer, the p-type impurity may be doped into both layers, or may be doped into either one of the layers.

The second nitride semiconductor layer 6 is desirably formed in contact with the first nitride semiconductor layer 5, but is not particularly required to be formed in contact therewith. For example, first and second
An undoped nitride semiconductor layer having a thickness of several hundred angstroms or less can be grown between the nitride semiconductor layer and the nitride semiconductor layer. The p-type impurity doped into the second nitride semiconductor layer 6 is desirably adjusted so as to be smaller than each of the first and third nitride semiconductor layers 5 and 6, specifically, 1 × 10 5 Less than ²⁰ / cm ³ , preferably below 1 × 10 ¹⁹ / cm ³ ,
More preferably, it is adjusted to 1 × 10 ¹⁸ / cm ³ . Also the second
The nitride semiconductor layer may not be doped with an impurity. Further, within this range, the number is adjusted so as to be smaller than that of each of the first and third nitride semiconductor layers. It is preferable that the p-type impurity concentration is within the above range for obtaining the effects of the present invention. The p-type impurity doped in the second nitride semiconductor layer may be the same as the impurity that can be doped in the first nitride semiconductor layer. The composition of the second nitride semiconductor layer is not particularly limited, but is preferably the same as that of the third nitride semiconductor layer. The thickness of the second nitride semiconductor layer is 2 μm.
m, more preferably 1 μm or less, most preferably 0.5 μm or less. When the film thickness is in this range, it is preferable in terms of light emission output and forward voltage. Further, the second nitride semiconductor layer may have a multilayer structure (including a superlattice) of a nitride semiconductor, and the p-type impurity concentration of the nitride semiconductor layer forming the multilayer film may be gradually reduced. .

The third nitride semiconductor layer 7 is preferably a contact layer for forming a p-electrode.
If the value is set to Al _x Ga ₁ -xN (0 ≦ X ≦ 0.3) having a value of 0.3 or less, a favorable ohmic is obtained with the p electrode. The p-type impurity concentration of the third nitride semiconductor layer 7 is 1 × 10 ¹⁸ / cm
³ or more and 1 × 10 ²¹ / cm ³ or less, preferably 1 × 10 ¹⁹ / cm ³
It is desirable to adjust to not less than cm ³ , more preferably to 2 × 10 ²⁰ / cm ³ . Also, within this range, the first and second
Is adjusted to be more than each of the nitride semiconductor layers. It is preferable that the p-type impurity concentration is within the above range for obtaining the effects of the present invention. It is preferable that the thickness of the third nitride semiconductor layer be adjusted to be smaller than that of the second nitride semiconductor layer. That is, the contact resistance is reduced by reducing the thickness of the third p-type nitride semiconductor layer acting as the contact layer and doping the p-type impurity with a high concentration, so that Vf (forward voltage) decreases. Tends to be easy. Specifically, the thickness of the third nitride semiconductor layer is adjusted to 1 μm or less, more preferably 0.1 μm or less, and most preferably 0.05 μm or less. When the film thickness is in this range, it is preferable in terms of light emission output and forward voltage.

[0013] The other structures constituting the nitride semiconductor device of the present invention are not particularly limited, and may be any as long as they satisfy at least the structure of the present invention.

[0014]

The present invention will now be described by way of examples, which should not be construed as limiting the invention. In the embodiment of the present invention, a MOCVD method is used as a method for forming a nitride semiconductor device.

Example 1 A substrate having a sapphire (0001) plane as a main surface was prepared, and a buffer layer made of GaN was formed at 200 ° C. at 500 ° C. using TMG (trimethylgallium) and ammonia as a source gas. Grow with.

Next, the temperature is raised to 1050 ° C. and TM
An n-type GaN layer doped with 1 × 10 ¹⁹ / cm ^{3 of} Si is grown to a thickness of 5 μm using G, ammonia, and a monosilane gas as an impurity gas.

Next, at a temperature of 800 ° C., a well layer of undoped In _0.4 Ga _0.6 N is grown to a thickness of 25 Å as an active layer using TMI (trimethyl indium), TMG and ammonia.

Next, the temperature is raised to 1050 ° C., TMG, ammonia, and Cp ₂ Mg (cyclopentadienyl magnesium) as an impurity gas, and Mg is added to 1 × 10 ¹⁹ / cm 2.
^A first nitride semiconductor layer made of ^3- doped p-type Al _0.3 Ga _0.7 N is grown to a thickness of 200 Å. This first nitride semiconductor layer functions as a layer for confining carriers.

After the growth of the first nitride semiconductor layer, the source gas is stopped, and then TMG, ammonia, and Cp ₂ Mg are again flowed, and a first layer of GaN doped with Mg at 1 × 10 ¹⁸ / cm ³ at 1050 ° C. 2 is grown to a thickness of 0.18 μm.

After the growth of the second nitride semiconductor layer, a third nitride semiconductor layer doped with 2 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 300 Å using TMG, ammonia and Cp ₂ Mg. .

The wafer on which the nitride semiconductor has been grown as described above is placed in a reaction vessel in a nitrogen atmosphere at 700.degree.
Annealing is performed at a temperature of ° C. to further reduce the resistance of the layer doped with the p-type impurity. After annealing, the wafer is taken out of the reaction container, and the wafer is etched from the third nitride semiconductor layer side of the uppermost layer by the RIE apparatus to expose the surface of the n-side contact layer on which the n-electrode is to be formed. A full-surface electrode made of Ni / Au is formed with a thickness of 200 Å on almost the entire surface of the third nitride semiconductor layer as the uppermost layer, and a pad electrode made of Au is formed with a thickness of 1 μm on a part of the whole electrode. I do. On the other hand, an n-electrode made of W and Au is formed on the exposed surface of the n-side contact layer.

The wafer on which the electrodes were formed as described above was separated into chips having a size of 350 μm square, and light was emitted.
At 0 mA, Vf 3.2 V, emission wavelength 525 nm,
The light output was 3.5 mW and the external quantum efficiency was 7.3%, which was about 1.3 times higher than the conventional green LED.

Example 2 In Example 1, the first nitride semiconductor layer was doped with Mg at 5 × 10 ¹⁹ / cm ³ ,
Is doped with 5 × 10 ¹⁷ / cm ³ of the nitride semiconductor layer,
When the third nitride semiconductor layer was doped with Mg at 1 × 10 ²⁰ / cm ³ and the other steps were performed in the same manner, an LED element having substantially the same characteristics as in Example 1 was obtained.

[Embodiment 3] FIG. 2 is a schematic sectional view showing the structure of one laser device according to the present invention. Hereinafter, a third embodiment of the present invention will be described with reference to FIG.

A GaN substrate 100 is prepared by growing a single crystal of GaN to a thickness of 120 μm on a substrate having a sapphire (0001) plane as a main surface via a buffer layer of GaN. With this GaN substrate 100 grown on sapphire, it was set in a reaction vessel, and the temperature was increased to 1050 ° C.
Ga doped with 1 × 10 ¹⁸ / cm ³ of Si on a substrate 100
An n-side buffer layer 11 of N is grown to a thickness of 4 μm. This n-side buffer layer is a buffer layer grown at a high temperature, for example, sapphire, Si
C, on a substrate made of a material different from a nitride semiconductor such as spinel,
It is distinguished from the buffer layer 2 in which AlN or the like is directly grown to a thickness of 0.5 μm or less.

(N-side cladding layer 12 = strained superlattice layer) Subsequently, n-type Al _0.3 doped with 1 × 10 ¹⁹ / cm ^{3 of} Si at 1050 ° C. using TMA (trimethylaluminum), TMG, ammonia and silane gas. A first layer of Ga _0.7 N is grown to a thickness of 40 Å, followed by stopping silane gas and TMA,
A second layer of aN is grown to a thickness of 40 Å. And the first layer + the second layer + the first layer + the second layer +
.. Constitute a strained superlattice layer,
The n-side cladding layer 12 composed of a strained superlattice having a total film thickness of 0.8 μm is alternately laminated by 00 layers.

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

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

(P-side cap layer 15)
Raise to 50 ° C, TMG, TMA, ammonia, Cp ₂ M
g (cyclopentadienyl magnesium), p-type Al _0.3 Ga doped with Mg at 1 × 10 ¹⁹ / cm ³ and having a larger band gap energy than the p-side light guide layer 16
_A p-side cap layer 17 of _0.7 N is grown to a thickness of 300 Å. 0.5μ for p-side cap layer
When the layer is grown to a thickness of not more than m, more preferably not more than 0.1 μm, the output is improved because the p-side cap layer functions as a barrier for confining carriers in the active layer. The lower limit of the thickness of the p-type cap layer 15 is not particularly limited, but is preferably formed to a thickness of 10 Å or more.

(P-side light guide layer 16) p-side cap layer 1
After 5 growth, the bandgap energy is smaller than that of the p-side cap layer 15 at 1050 ° C. in the same manner as in Example 1 using TMG, Cp ₂ Mg, and ammonia again.
A p-side optical guide layer 16 made of GaN doped with 1 × 10 ²⁰ / cm ³ is grown to a thickness of 0.1 μm. This layer acts as a light guide layer for the active layer.

(P-side cladding layer 17 = first nitride semiconductor layer) Subsequently, a layer made of p-type Al _0.3 Ga _0.8 N doped with Mg at 1 × 10 ²⁰ / cm ³ at 1050 ° C. is a 40 angstrom film. Then, only TMA is stopped, and a layer made of p-type GaN doped with Mg at 1 × 10 ¹⁹ / cm ³ is grown to a thickness of 40 Å. This operation is repeated 100 times, and the total film thickness is set to 0.
A p-side cladding layer 17 made of a strained superlattice layer of 8 μm is formed. The average concentration of Mg in the p-side cladding layer is 5 × 10
¹⁹ / cm ³ .

(P-side contact layer 18 = second and third nitride semiconductor layers) Finally, at 1050 ° C., p-type doped with 1 × 10 ¹⁸ / cm ^{3 of} Mg on the p-side cladding layer 17 0.1 μm of GaN layer (second nitride semiconductor layer)
Then, a layer (third nitride semiconductor layer) made of p-type GaN doped with Mg at 2 × 10 ²⁰ / cm ³ is grown to a thickness of 200 Å. p
The side contact layer 18 is a p-type In _x Al _Y Ga _{1 -XYN}
(0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably Mg-doped GaN, the p-electrode 21
And the most preferable ohmic contact is obtained. Also p-type A
p-side cladding layer 1 having a strained superlattice structure containing l _Y Ga _1-Y N
7, the nitride semiconductor having a small band gap energy is used as the p-side contact layer, and its thickness is reduced to 500 Å or less.
The carrier concentration of the side contact layer 18 is increased, a favorable ohmic contact with the p-electrode is obtained, and the threshold current and voltage of the device are reduced.

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

After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 2, the uppermost p-side contact layer 18 and p-side clad layer 17 are etched by an RIE apparatus to have a stripe width of 4 μm. Ridge shape. As described above, by forming the layer above the active layer into a stripe-shaped ridge, light emission of the active layer is concentrated below the stripe ridge, and the threshold value is reduced. In particular, it is preferable that a layer of the p-side cladding layer 17 or more composed of the strained superlattice layer has a ridge shape.

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

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

After the electrodes are formed, the GaN substrate is cleaved on the M plane (a plane corresponding to the side surface of a hexagonal prism when the nitride semiconductor is approximated by a hexagonal system), and the cleavage plane is formed of a dielectric material composed of SiO ₂ and TiO _2. A multilayer film is formed, and finally, in a direction parallel to the p-electrode,
The bar is cut to form a laser element.

This laser chip was placed face-up (in a state where the substrate and the heat sink faced each other), and the electrodes were wire-bonded to perform laser oscillation at room temperature. At 0.0 kA / cm ² and a threshold voltage of 4.0 V, continuous oscillation at an oscillation wavelength of 405 nm was confirmed, and a life of 1000 hours or more was shown.

[0039]

As described above, according to the method for forming a nitride semiconductor device of the present invention, the concentration of the p-type impurity in the plurality of nitride semiconductor layers stacked on the active layer is defined within a specific range, and By specifying the order of the steps, the output of the nitride semiconductor device can be significantly improved. Further, the method of forming an element of the present invention can be used not only for light-emitting devices such as LEDs and LDs, but also for many electronic devices using nitride semiconductors such as other light-receiving devices.

[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 an LD device according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 3 ... n-side contact layer 4 ... Active layer 5 ... 1st p-side nitride semiconductor layer 6 ... 2nd p-side nitride semiconductor Layer 7: Third p-side nitride semiconductor layer 8: P electrode 9: Pad electrode 10: N electrode

Claims (4)

[Claims] 1. An active layer forming step of forming an active layer including at least a nitride semiconductor layer, and a first nitride semiconductor layer forming a first nitride semiconductor layer containing a p-type impurity on the active layer. Forming a second nitride semiconductor layer on the first nitride semiconductor layer, the second nitride semiconductor layer containing a smaller amount of p-type impurities than the p-type impurity concentration of the first nitride semiconductor layer Forming a third nitride semiconductor layer on the second nitride semiconductor layer, the third nitride semiconductor layer containing a larger amount of p-type impurities than the p-type impurity concentration of the first nitride semiconductor layer; A method for forming a nitride semiconductor device, comprising at least a step of forming a nitride semiconductor layer. 2. The method for forming a nitride semiconductor device according to claim 1, wherein the p-type impurity concentration of the first nitride semiconductor layer is 1 × 10 ¹⁷ or more and 1 × 10 ²⁰ or less. . 3. The method for forming a nitride semiconductor device according to claim 1, wherein the p-type impurity concentration of the second nitride semiconductor layer is less than 1 × 10 ²⁰ . 4. The method according to claim 1, wherein the p-type impurity concentration of the third nitride semiconductor layer is not less than 1 × 10 ^{18 and not} more than 1 × 10 ²¹ . A method for forming a nitride semiconductor device.