CN115881866B - LED epitaxial wafer, preparation method thereof and LED - Google Patents

Abstract

The invention discloses a light-emitting diode epitaxial wafer and a preparation method thereof, and an LED, wherein the light-emitting diode epitaxial wafer comprises a substrate, and a buffer layer, an undoped GaN layer, an N-type GaN layer, an active layer, an electron blocking layer and a P-type GaN layer which are sequentially laminated on the substrate; the buffer layer comprises a Cr layer and an Al layer sequentially laminated on the substrate _1‑x Cr _x An N layer, an AlN layer and an Al doped GaN layer, wherein, the value range of x is 0.1-1. The light-emitting diode epitaxial wafer provided by the invention can reduce lattice mismatch and thermal mismatch, reduce defect density, improve crystal quality, improve quantum well radiation recombination efficiency and improve light-emitting efficiency of the light-emitting diode.

Description

LED epitaxial wafer, preparation method thereof and LED

Technical Field

The invention relates to the technical field of photoelectricity, in particular to a light-emitting diode epitaxial wafer, a preparation method thereof and an LED.

Background

Group iii nitrides mainly include aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), and alloy materials thereof, and their forbidden band widths can be continuously adjustable between 6.2eV of AlN to 0.7eV of InN by changing the component contents of Al, ga, in the alloy thereof. The light-emitting range can be covered from an ultraviolet band of 200nm to an infrared band of 1770nm, so that the GaN-based alloy material can be used for manufacturing an infrared-to-ultraviolet light-emitting diode and a laser diode. Because the III nitride LED corresponds to a larger wave band and has excellent performance, the attention of academia and industry is gradually improved, and the III nitride light-emitting device gradually enters the life of people, at present, the main application of the III nitride LED comprises the fields of a display screen backlight source, outdoor display, illumination, traffic lights, car lights and the like, almost every corner in our life has the body shadow of the LED, the application field of the III nitride LED is continuously widened, and the market value of the III nitride LED is continuously improved.

For GaN-based LEDs, the most ideal substrate material is the GaN material itself. However, the GaN single crystal substrate is difficult to prepare and has a high cost. Therefore, epitaxy of GaN materials is often performed on heterogeneous substrates, with sapphire (α -Al) being the currently commonly used substrate material ₂ O ₃ ) Silicon carbide (6H-SiC) and silicon (Si). Of these, sapphire substrates are most commonly used, but there is a lattice mismatch of about 13.3% and a thermal expansion coefficient mismatch of about 25.5% between sapphire and GaN. A large lattice mismatch will result in about 10 in GaN epitaxial material ⁸ cm ^-3 Dislocation of density. These dislocations can act as non-radiative recombination centers, causing carriers to be trapped by defects, reducing carrier lifetime and mobility, severely affecting LED performance. The large thermal mismatch causes huge compressive stress in the epitaxial layer in the cooling process, and even a large number of cracks can be generated in the epitaxial wafer in severe cases.

Disclosure of Invention

The invention aims to solve the technical problem of providing a light-emitting diode epitaxial wafer, which reduces lattice mismatch and thermal mismatch, reduces defect density, improves crystal quality, improves quantum well radiation recombination efficiency and improves light-emitting efficiency of a light-emitting diode.

The invention also aims to provide a preparation method of the light-emitting diode epitaxial wafer, which has simple process and can stably prepare the light-emitting diode epitaxial wafer with good luminous efficiency.

In order to solve the technical problems, the invention provides a light-emitting diode epitaxial wafer, which comprises a substrate, and a buffer layer, an undoped GaN layer, an N-type GaN layer, an active layer, an electron blocking layer and a P-type GaN layer which are sequentially laminated on the substrate;

the buffer layer comprises a Cr layer and an Al layer sequentially laminated on the substrate _1-x Cr _x An N layer, an AlN layer and an Al doped GaN layer, wherein, the value range of x is 0.1-1.

In one embodiment, the Al _1-x Cr _x In the N layer, the Cr component content gradually decreases from being close to the substrate to being far away from the substrate;

in the Al-doped GaN layer, the content of Al components gradually decreases from being close to the substrate to being far away from the substrate.

Preferably, the Al _1-x Cr _x In the N layer, the Cr component content gradually decreases from (0.5-1) to (0.1-0.5) from the substrate to the substrate.

Preferably, in the Al-doped GaN layer, the Al component content gradually decreases from (0.6-1) to (0.1-0.5) from the direction approaching the substrate to the direction separating from the substrate.

In one embodiment, the Cr layer has a thickness of 0.5nm to 5nm;

the Al is _1-x Cr _x The thickness of the N layer is 1nm-20nm;

the thickness of the AlN layer is 5nm-50nm;

the thickness of the Al doped GaN layer is 10nm-100nm.

In order to solve the problems, the invention also provides a preparation method of the light-emitting diode epitaxial wafer, which comprises the following steps:

s1, preparing a substrate;

s2, sequentially depositing a buffer layer, an undoped GaN layer, an N-type GaN layer, an active layer, an electron blocking layer and a P-type GaN layer on the substrate;

growing a buffer layer on the substrate, comprising:

sequentially depositing Cr layer and Al on the substrate _1-x Cr _x The buffer layer is obtained by the N layer, the AlN layer and the Al doped GaN layer, wherein the value range of x is 0.1-1.

In one embodiment, the growing a buffer layer on the substrate further comprises:

carrying out heat treatment on the AlN layer before the Al-doped GaN layer is deposited;

the heat treatment includes: at H ₂ In the atmosphere, at 1100-1300 DEG CThermal annealing is performed.

In one embodiment, the Cr layer, al _1-x Cr _x The N layer or AlN layer is deposited by the following method:

the sputtering power of the reaction chamber is controlled to be 2KW-5KW, the sputtering temperature is 300 ℃ to 800 ℃, the sputtering pressure is 1torr-50torr, and the sputtering atmosphere is N ₂ And Ar, introducing materials to finish sputtering deposition.

In one embodiment, the Al doped GaN layer is deposited by the following method:

the temperature of the reaction chamber is controlled to be 700-900 ℃, the pressure is controlled to be 50-300 torr, and the sputtering atmosphere is N ₂ And NH ₃ And introducing an Al source, a Ga source and an N source to finish deposition.

Correspondingly, the invention further provides an LED, and the LED comprises the LED epitaxial wafer.

The implementation of the invention has the following beneficial effects:

the invention provides a light-emitting diode epitaxial wafer, wherein the buffer layer comprises a Cr layer and an Al layer which are sequentially laminated on a substrate _1-x Cr _x An N layer, an AlN layer and an Al doped GaN layer, wherein, the value range of x is 0.1-1. The nucleation size of the Cr layer on the sapphire substrate is regulated and controlled at the initial stage of AlN, so that the AlN recrystallization efficiency is effectively improved, and the potential barrier of crystal axis torsion is reduced. The Al is _1-x Cr _x The introduction of Cr into the N layer is beneficial to improving the crystal quality and strain relaxation, thereby greatly improving the photoelectric performance of the device. The AlN layer controls crystal defects, improves the quality of the subsequently grown crystal, provides a nucleation point for the subsequent GaN growth, and is beneficial to the film formation of the GaN epitaxial material and the improvement of the crystal quality. The Al doped GaN layer can relieve stress between the AlN layer and the GaN epitaxial layer caused by lattice mismatch and thermal mismatch, and improves the crystal quality of the subsequent deposited GaN epitaxial layer. The four sublayers of the buffer layer cooperate with each other to finally reduce lattice mismatch and thermal mismatch, reduce defect density, improve crystal quality, improve quantum well radiation recombination efficiency and improve luminous efficiency of the light-emitting diode.

Drawings

Fig. 1 is a schematic structural diagram of an led epitaxial wafer according to the present invention.

Wherein: substrate 1, buffer layer 2, undoped GaN layer 3, N-type GaN layer 4, active layer 5, electron blocking layer 6, P-type GaN layer 7, cr layer 21, al _1-x Cr _x An N layer 22, an AlN layer 23, and an Al-doped GaN layer 24.

Detailed Description

The present invention will be described in further detail below in order to make the objects, technical solutions and advantages of the present invention more apparent.

Unless otherwise indicated or contradicted, terms or phrases used herein have the following meanings:

in the present invention, "preferred" is merely to describe embodiments or examples that are more effective, and it should be understood that they are not intended to limit the scope of the present invention.

In the invention, the technical characteristics described in an open mode comprise a closed technical scheme composed of the listed characteristics and also comprise an open technical scheme comprising the listed characteristics.

In the present invention, the numerical range is referred to, and both ends of the numerical range are included unless otherwise specified.

In order to solve the above problems, the present invention provides a light emitting diode epitaxial wafer, as shown in fig. 1, comprising a substrate 1, and a buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, an active layer 5, an electron blocking layer 6, and a P-type GaN layer 7 sequentially stacked on the substrate 1;

the buffer layer 2 comprises a Cr layer 21 and Al sequentially laminated on the substrate 1 _1-x Cr _x An N layer 22, an AlN layer 23 and an Al doped GaN layer 24, wherein the value of x is in the range of 0.1-1.

The Cr layer 21 regulates and controls the nucleation size of AlN which is epitaxially grown on the sapphire substrate 1 in the initial stage, so that the AlN recrystallization efficiency is effectively improved, and the potential barrier of crystal axis torsion is reduced. The Al is _1-x Cr _x The introduction of Cr into the N layer 22 is beneficial to improving crystal quality and strain relaxation, thereby greatly improving the optoelectronic performance of the device. The AlN layer 23 controls crystal defects, improves the quality of the crystal to be grown subsequently, provides nucleation sites for the growth of GaN to be grown subsequently, and is beneficialFilm formation and crystal quality improvement of GaN epitaxial material. The Al doped GaN layer 24 can relieve stress between the AlN layer 23 and the GaN epitaxial layer caused by lattice mismatch and thermal mismatch, and improve the crystal quality of the GaN epitaxial layer deposited later. The four sub-layers of the buffer layer 2 cooperate with each other to finally reduce lattice mismatch and thermal mismatch, reduce defect density, improve crystal quality, improve quantum well radiation recombination efficiency and improve luminous efficiency of the light-emitting diode.

In one embodiment, the Al _1-x Cr _x In the N layer 22, the Cr component content gradually decreases from the vicinity of the substrate 1to the direction away from the substrate 1; preferably, the Al _1-x Cr _x In the N layer 22, the Cr component content gradually decreases from (0.5-1) to (0.1-0.5) in a direction from approaching the substrate 1to separating from the substrate 1. In one embodiment, the Al-doped GaN layer 24 has an Al component content gradually decreasing from the direction closer to the substrate 1to the direction farther from the substrate 1. Preferably, in the Al-doped GaN layer 24, the Al component content gradually decreases from (0.6-1) to (0.1-0.5) in a direction from approaching the substrate 1to separating from the substrate 1. The Al component content gradually decreases along the direction of the epitaxial layer, so that the lattice mismatch between the substrate 1 and the GaN epitaxial layer can be reduced, and the crystal quality can be improved.

In addition, the thickness of each layer of the buffer layer 2 also affects the light emitting efficiency of the final light emitting diode. In one embodiment, the Cr layer 21 has a thickness of 0.5nm to 5nm; the Al is _1-x Cr _x The thickness of the N layer 22 is 1nm-20nm; the thickness of the AlN layer 23 is 5nm-50nm; the thickness of the Al doped GaN layer 24 is 10nm-100nm. It should be noted that, too thick Cr layer 21 will cause too large thermal expansion coefficient of the buffer layer 2 deposited later, and serious crack of the epitaxial layer; the Al is _1-x Cr _x The thickness of the N layer 22, the AlN layer 23 or the Al doped GaN layer 24 in the above range can not only avoid the degradation of crystal quality caused by too thick buffer thickness, but also reduce the lattice mismatch between the GaN epitaxial layer and the substrate 1, improve the crystal quality of the GaN epitaxial layer, reduce the extension of the deposition direction of the defect epitaxial layer, and reduce the light emitting efficiency of the light emitting diode.

Correspondingly, the invention provides a preparation method of the light-emitting diode epitaxial wafer, which comprises the following steps:

s1, preparing a substrate 1;

in one embodiment, the substrate 1 is a sapphire substrate 1; sapphire is the most commonly used substrate 1 material at present, and the sapphire substrate has the advantages of mature preparation process, low price, easy cleaning and processing and good stability at high temperature.

S2, a buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, an active layer 5, an electron blocking layer 6 and a P-type GaN layer 7 are sequentially deposited on the substrate 1.

In one embodiment, step S2 comprises the steps of:

s21, growing a buffer layer 2 on the substrate 1, including:

sequentially depositing Cr layers 21 and Al on the substrate 1 _1-x Cr _x The buffer layer 2 is obtained by an N layer 22, an AlN layer 23 and an Al doped GaN layer 24, wherein the value range of x is 0.1-1.

Preferably, the buffer layer 2 on the substrate 1 further includes: heat treating the AlN layer 23 prior to deposition of the Al-doped GaN layer 24; the heat treatment includes: at H ₂ And (3) performing thermal annealing at 1100-1300 ℃ in the atmosphere. The introduction of the heat treatment matched with Cr can obviously improve the crystal quality and the strain relaxation, thereby greatly improving the photoelectric performance of the device.

Preferably, the Cr layer 21, al _1-x Cr _x The N layer 22 or AlN layer 23 is deposited by the following method: the sputtering power of the reaction chamber is controlled to be 2KW-5KW, the sputtering temperature is 300 ℃ to 800 ℃, the sputtering pressure is 1torr-50torr, and the sputtering atmosphere is N ₂ Ar is introduced into the material to finish sputtering deposition;

the Al doped GaN layer 24 is deposited by the following method: the temperature of the reaction chamber is controlled to be 700-900 ℃, the pressure is controlled to be 50-300 torr, and the sputtering atmosphere is N ₂ And NH ₃ And introducing an Al source, a Ga source and an N source to finish deposition.

S22, depositing an undoped GaN layer 3 on the buffer layer 2.

Preferably, the growth temperature of the undoped GaN layer 3 is 1050-1200 ℃, the pressure is 100-600 torr, and the thickness is 1-5 μm. More preferably, the undoped GaN layer 3 is grown at 1100 ℃ under a growth pressure of 150torr and a growth thickness of 2 μm-3 μm. The undoped GaN layer 3 has higher growth temperature and lower pressure, the prepared GaN crystals have better quality, meanwhile, the thickness is increased along with the increase of the thickness of the GaN, the compressive stress can be released through stacking faults, the line defects are reduced, the crystal quality is improved, the reverse leakage is reduced, but the consumption of Ga source materials by the thickness of the GaN layer is increased, and the epitaxial cost of an LED is greatly increased, so that the thickness of the undoped GaN layer 3 of the conventional LED epitaxial wafer is 2-3 mu m, the production cost is saved, and the GaN material has higher crystal quality.

S23, depositing an N-type GaN layer 4 on the undoped GaN layer 3.

Preferably, the growth temperature of the N-type GaN layer 4 is 1050-1200 ℃, the pressure is 100-600 torr, the thickness is 2-3 μm, and the Si doping concentration is 1X 10 ¹⁹ atoms/cm ³ -5×10 ¹⁹ atoms/cm ³ 。

More preferably, the growth temperature of the N-type GaN layer 4 is 1120 ℃, the growth pressure is 100torr, the growth thickness is 2 μm-3 μm, and the Si doping concentration is 2.5X10 ¹⁹ atoms/cm ³ . The N-type GaN layer 4 provides sufficient electrons for the LED to emit light, and the resistivity of the N-type GaN layer 4 is higher than that of the transparent electrode on the P-type GaN layer 7, so that the N-type GaN layer 4 has sufficient Si doping, and the N-type GaN layer 4 has sufficient thickness to effectively release the luminous efficiency of the stress LED.

And S24, growing an active layer 5 on the N-type GaN layer 4.

Preferably, the active layer 5 is an InGaN quantum well layer and an AlGaN quantum barrier layer which are alternately stacked, and the stacking period is 6-12, wherein the growth temperature of the InGaN quantum well layer is 790-810 ℃, the thickness of the InGaN quantum well layer is 2-5 nm, and the growth pressure is 50-300 torr; the AlGaN quantum barrier layer has a growth temperature of 800-900 ℃, a thickness of 5-15 nm, a growth pressure of 50-300 torr and an Al component content of 0.01-0.1.

More preferably, the active layer 5 is an InGaN quantum well layer and an AlGaN quantum barrier layer which are alternately stacked, the stacking period number is 10, wherein the growth temperature of the InGaN quantum well layer is 795 ℃, the thickness is 3.5nm, the pressure is 200torr, and the in component content is 0.22; the AlGaN quantum barrier layer has a growth temperature of 855 ℃, a thickness of 9.8nm, a growth pressure of 200torr and an Al component content of 0.05. The active layer 5 is an electron and hole recombination region, and the reasonable structural design can obviously increase the overlapping degree of electron and hole wave functions, so that the luminous efficiency of the LED device is improved.

And S25, growing an electron blocking layer 6 on the active layer 5.

Preferably, the electron blocking layer 6 is an AlInGaN layer with a thickness of 10nm-40nm, a growth temperature of 900-1000 ℃ and a pressure of 100-300 torr, wherein the Al component content is 0.005-0.1, and the in component content is 0.01-0.2.

More preferably, the electron blocking layer 6 is an AlInGaN layer with a thickness of 15nm, wherein the Al component content gradually changes from 0.01 to 0.05 along the growth direction of the epitaxial layer, the in component content is 0.01, and the growth temperature is 965 ℃ and the growth pressure is 200torr. The electron blocking layer 6 can not only effectively limit electron overflow, but also reduce blocking of holes, and improve injection efficiency of the holes into the quantum wells.

And S26, growing a P-type GaN layer 7 on the electron blocking layer 6.

Preferably, the growth temperature of the P-type GaN layer 7 is 900-1050 ℃, the thickness is 10-50 nm, the growth pressure is 100-600 torr, and the doping concentration of Mg is 1X 10 ¹⁹ atoms/cm ³ -1×10 ²¹ atoms/cm ³ 。

More preferably, the growth temperature of the P-type GaN layer 7 is 985 ℃, the thickness is 15nm, the growth pressure is 200torr, and the doping concentration of Mg is 2 multiplied by 10 ²⁰ atoms/cm ³ . Too high a Mg doping concentration can damage the crystal quality, while a lower doping concentration can affect the hole concentration. Meanwhile, for the LED structure containing the V-shaped pits, the higher growth temperature of the P-type GaN layer 7 is favorable for combining the V-shaped pits, so that the LED epitaxial wafer with a smooth surface is obtained.

Correspondingly, the invention further provides an LED, and the LED comprises the LED epitaxial wafer. The photoelectric efficiency of the LED is effectively improved, and other items have good electrical properties.

The invention is further illustrated by the following examples:

example 1

The embodiment provides a light-emitting diode epitaxial wafer, which comprises a substrate, and a buffer layer, an undoped GaN layer, an N-type GaN layer, an active layer, an electron blocking layer and a P-type GaN layer which are sequentially laminated on the substrate;

the buffer layer comprises a Cr layer and an Al layer sequentially laminated on the substrate _1-x Cr _x An N layer, an AlN layer and an Al doped GaN layer;

wherein the Al is _1-x Cr _x In the N layer, the Cr component content gradually decreases from 0.6 to 0.1 from the substrate to the substrate;

in the Al doped GaN layer, the content of Al components gradually decreases from 0.7 to 0.1 from the direction from the substrate to the substrate;

the thickness of the Cr layer is 3nm; the Al is _1-x Cr _x The thickness of the N layer is 10nm; the thickness of the AlN layer is 25nm; the thickness of the Al doped GaN layer is 55nm.

Example 2

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: the thickness of the Cr layer is 1nm; the Al is _1-x Cr _x The thickness of the N layer is 10nm; the thickness of the AlN layer is 25nm; the thickness of the Al doped GaN layer is 55nm. The remainder was the same as in example 1.

Example 3

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: the thickness of the Cr layer is 3nm; the Al is _1-x Cr _x The thickness of the N layer is 15nm; the thickness of the AlN layer is 25nm; the thickness of the Al doped GaN layer is 55nm. The remainder was the same as in example 1.

Example 4

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: the thickness of the Cr layer is 3nm; the Al is _1-x Cr _x The thickness of the N layer is 15nm; the thickness of the AlN layer is 35nm; the saidThe thickness of the Al doped GaN layer was 55nm. The remainder was the same as in example 1.

Example 5

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: the thickness of the Cr layer is 3nm; the Al is _1-x Cr _x The thickness of the N layer is 10nm; the thickness of the AlN layer is 25nm; the thickness of the Al doped GaN layer is 65nm. The remainder was the same as in example 1.

Example 6

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: the Al is _1-x Cr _x In the N layer, the Cr component content gradually decreases from 1to 0.5 from the substrate to the substrate. The remainder was the same as in example 1.

Example 7

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: the Al is _1-x Cr _x In the N layer, the Cr component content gradually decreases from 0.5 to 0.1 from the substrate to the substrate. The remainder was the same as in example 1.

Example 8

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: in the Al doped GaN layer, the content of Al component gradually decreases from 1to 0.5 from the direction close to the substrate to the direction far away from the substrate. The remainder was the same as in example 1.

Example 9

The present embodiment provides a light emitting diode epitaxial wafer, which is different from embodiment 1 in that: in the Al doped GaN layer, the content of Al component gradually decreases from 0.6 to 0.1 from the direction close to the substrate to the direction far away from the substrate. The remainder was the same as in example 1.

Comparative example 1

This comparative example differs from example 1 in that the buffer layer is a 35nm AlN buffer layer, and the remainder is the same as example 1.

The light-emitting diode epitaxial wafers prepared in example 1-example 9 and comparative example 1 were prepared into 10×24mil chips using the same chip process conditions, 300 LED chips were extracted, the photoelectric properties of the chips were tested, and the light efficiency improvement rates of example 1-example 9 relative to comparative example 1 were calculated, and the specific test results are shown in table 1.

TABLE 1 example 1-example 9 Performance test results of LEDs

From the above results, the buffer layer of the LED epitaxial wafer provided by the present invention comprises a Cr layer and an Al layer sequentially laminated on the substrate _1-x Cr _x An N layer, an AlN layer and an Al doped GaN layer, wherein, the value range of x is 0.1-1. The nucleation size of the Cr layer on the sapphire substrate is regulated and controlled at the initial stage of AlN, so that the AlN recrystallization efficiency is effectively improved, and the potential barrier of crystal axis torsion is reduced. The Al is _1-x Cr _x The introduction of Cr into the N layer is beneficial to improving the crystal quality and strain relaxation, thereby greatly improving the photoelectric performance of the device. The AlN layer controls crystal defects, improves the quality of the subsequently grown crystal, provides a nucleation point for the subsequent GaN growth, and is beneficial to the film formation of the GaN epitaxial material and the improvement of the crystal quality. The Al doped GaN layer can relieve stress between the AlN layer and the GaN epitaxial layer caused by lattice mismatch and thermal mismatch, and improves the crystal quality of the subsequent deposited GaN epitaxial layer. The four sublayers of the buffer layer cooperate with each other to finally reduce lattice mismatch and thermal mismatch, reduce defect density, improve crystal quality, improve quantum well radiation recombination efficiency and improve luminous efficiency of the light-emitting diode.

While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the principles of the invention, such changes and modifications are also intended to be within the scope of the invention.

Claims (7)

1. The light-emitting diode epitaxial wafer is characterized by comprising a substrate, and a buffer layer, an undoped GaN layer, an N-type GaN layer, an active layer, an electron blocking layer and a P-type GaN layer which are sequentially laminated on the substrate;

the buffer layer comprises a Cr layer and an Al layer sequentially laminated on the substrate _1-x Cr _x An N layer, an AlN layer and an Al doped GaN layer;

the Al is _1-x Cr _x In the N layer, the Cr component content gradually decreases from being close to the substrate to being far away from the substrate;

in the Al-doped GaN layer, the content of Al components gradually decreases from being close to the substrate to being far away from the substrate;

the Al is _1-x Cr _x In the N layer, the Cr component content gradually decreases from (0.5-1) to (0.1-0.5) from the substrate to the substrate;

in the Al doped GaN layer, the content of Al component gradually decreases from (0.6-1) to (0.1-0.5) from the direction from the substrate to the substrate;

the Al is _1-x Cr _x The N layer is deposited by the following method:

the sputtering power of the reaction chamber is controlled to be 2KW-5KW, the sputtering temperature is 300 ℃ to 800 ℃, the sputtering pressure is 1torr-50torr, and the sputtering atmosphere is N ₂ And Ar, introducing materials to finish sputtering deposition.

2. The light-emitting diode epitaxial wafer of claim 1, wherein the Cr layer has a thickness of 0.5nm to 5nm;

the Al is _1-x Cr _x The thickness of the N layer is 1nm-20nm;

the thickness of the AlN layer is 5nm-50nm;

the thickness of the Al doped GaN layer is 10nm-100nm.

3. A method for preparing the light-emitting diode epitaxial wafer according to any one of claims 1to 2, comprising the steps of:

s1, preparing a substrate;

s2, sequentially depositing a buffer layer, an undoped GaN layer, an N-type GaN layer, an active layer, an electron blocking layer and a P-type GaN layer on the substrate;

growing a buffer layer on the substrate, comprising:

sequentially depositing Cr layer and Al on the substrate _1-x Cr _x The buffer layer is obtained by the N layer, the AlN layer and the Al doped GaN layer, wherein the value range of x is 0.1-1.

4. The method for preparing a light emitting diode epitaxial wafer according to claim 3, wherein growing a buffer layer on the substrate further comprises:

carrying out heat treatment on the AlN layer before the Al-doped GaN layer is deposited;

the heat treatment includes: at H ₂ And (3) performing thermal annealing at 1100-1300 ℃ in the atmosphere.

5. The method for manufacturing a light-emitting diode epitaxial wafer according to claim 3, wherein the Cr layer and Al layer _1-x Cr _x The N layer or AlN layer is deposited by the following method:

the sputtering power of the reaction chamber is controlled to be 2KW-5KW, the sputtering temperature is 300 ℃ to 800 ℃, the sputtering pressure is 1torr-50torr, and the sputtering atmosphere is N ₂ And Ar, introducing materials to finish sputtering deposition.

6. The method for preparing a light-emitting diode epitaxial wafer according to claim 3, wherein the Al-doped GaN layer is deposited by the following method:

the temperature of the reaction chamber is controlled to be 700-900 ℃, the pressure is controlled to be 50-300 torr, and the sputtering atmosphere is N ₂ And NH ₃ And introducing an Al source, a Ga source and an N source to finish deposition.

7. An LED comprising the light emitting diode epitaxial wafer according to any one of claims 1-2.

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