CN109904066B

CN109904066B - Preparation method of GaN-based light-emitting diode epitaxial wafer

Info

Publication number: CN109904066B
Application number: CN201910069065.4A
Authority: CN
Inventors: 曹阳; 乔楠; 王群; 郭炳磊; 吕蒙普; 胡加辉; 李鹏
Original assignee: HC Semitek Zhejiang Co Ltd
Current assignee: HC Semitek Zhejiang Co Ltd
Priority date: 2019-01-24
Filing date: 2019-01-24
Publication date: 2021-10-01
Anticipated expiration: 2039-01-24
Also published as: CN109904066A

Abstract

The invention discloses a preparation method of a GaN-based light-emitting diode epitaxial wafer, belonging to the field of GaN-based light-emitting diodes. The method comprises the following steps: providing a substrate; depositing a buffer layer, an undoped GaN layer, an N-type GaN layer, a defect barrier layer, a multi-quantum well layer, an electronic barrier layer, a P-type GaN layer and a P-type contact layer on the substrate in sequence, wherein the P-type GaN layer comprises a first GaN sublayer and a second GaN sublayer, the first GaN sublayer is positioned between the electronic barrier layer and the second GaN sublayer, and the N-type GaN layer is adopted during deposition of the first GaN sublayer₂And H₂The mixed gas is used as a carrier gas, and N is adopted when the second GaN sub-layer is deposited₂As a carrier gas.

Description

Preparation method of GaN-based light-emitting diode epitaxial wafer

Technical Field

The invention relates to the field of GaN-based light emitting diodes, in particular to a preparation method of a GaN-based light emitting diode epitaxial wafer.

Background

A GaN (gallium nitride) -based LED (Light Emitting Diode), also called a GaN-based LED chip, generally includes an epitaxial wafer and an electrode fabricated on the epitaxial wafer. The epitaxial wafer generally comprises: a substrate, and a GaN-based epitaxial layer grown on the substrate. The GaN-based epitaxial layer includes a buffer layer, an undoped GaN layer, an N-type GaN layer, an MQW (multi Quantum Well) layer, an electron blocking layer, a P-type GaN layer, and a contact layer, which are sequentially stacked. When current is injected into the GaN-based LED, electrons in an N-type region such as an N-type GaN layer and holes in a P-type region such as a P-type GaN layer enter the MQW active region and recombine to emit visible light.

The conventional P-type GaN layer is generally formed by MOCVD (Metal-organic Chemical Vapor Deposition)Phase precipitation) method, in the MOCVD method, N is used₂And H₂Mixed gas as carrier gas, NH₃As the nitrogen source, trimethyl gallium or triethyl gallium is used as the gallium source. The P-type GaN layer thus grown has a low hole concentration.

Disclosure of Invention

The embodiment of the invention provides a preparation method of a GaN-based light emitting diode epitaxial wafer, which can effectively improve the hole concentration of a P-type GaN layer. The technical scheme is as follows:

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

providing a substrate;

depositing a buffer layer, an undoped GaN layer, an N-type GaN layer, a defect barrier layer, a multi-quantum well layer, an electronic barrier layer, a P-type GaN layer and a P-type contact layer on the substrate in sequence, wherein the P-type GaN layer comprises a first GaN sublayer and a second GaN sublayer, the first GaN sublayer is positioned between the electronic barrier layer and the second GaN sublayer, and the N-type GaN layer is adopted during deposition of the first GaN sublayer₂And H₂The mixed gas is used as a carrier gas, and N is adopted when the second GaN sub-layer is deposited₂As a carrier gas.

Optionally, in the mixed gas, N₂And H₂The flow ratio of (1): 10-1: 2.

optionally, in the mixed gas, N₂The flow rate of (A) is more than or equal to 20L/min, H₂The flow rate of (A) is less than or equal to 100L/min.

Optionally, N is added during deposition of the second GaN sub-layer₂The flow rate of (A) is 20 to 100L/min.

Optionally, the growth temperature of the first GaN sublayer is 900-1000 ℃, and the growth temperature of the second GaN sublayer is 930-1050 ℃.

Optionally, the growth pressure of the first GaN sublayer and the growth pressure of the second GaN sublayer are both 100-300 Torr.

Optionally, the thickness of the first GaN sublayer is 10-50 nm, and the thickness of the second GaN sublayer is 50-100 nm.

Optionally, theThe first GaN sublayer and the second GaN sublayer are both doped with Mg, and the Mg doping concentration in the first GaN sublayer is 10¹⁸～10¹⁹cm^-3And the Mg doping concentration in the second GaN sublayer is higher than that in the first GaN sublayer.

Optionally, the electron blocking layer is Al_xGa_1-xN layer, 0.1<x<0.5。

Optionally, the electron blocking layer is doped with Mg, and the doping concentration of Mg is 2 x 10¹⁷～2×10¹⁸cm^-3。

The technical scheme provided by the embodiment of the invention has the following beneficial effects: the P-type GaN layer comprises a first GaN sub-layer and a second GaN sub-layer, and N is adopted during deposition of the first GaN sub-layer₂And H₂The mixed gas is used as a carrier gas, and N is adopted when the second GaN sub-layer is deposited₂As carrier gas, the first GaN sublayer is positioned between the electron blocking layer and the second GaN sublayer, so that the P-type GaN layer is divided into two sections for growth, and the second GaN sublayer only adopts N₂As a carrier gas, H is reduced compared to a conventional P-type GaN layer₂The introduction of the compound reduces the formation of Mg-H compound, avoids non-radiative recombination caused by taking a deep energy level receptor caused by the Mg-H compound as a hole trap, and improves the hole concentration. At the same time, the latter section only adopts N₂As carrier gas, in pure N₂A smoother planar layer (namely a second GaN sublayer) is obtained in a high-temperature environment compared with the previous section, and V-shaped defects extending upwards from the MQW layer can be inhibited, so that the quality of grown crystals of the P-type GaN layer is higher, and the hole concentration is further improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a flow chart of a method for fabricating an epitaxial wafer of a GaN-based light emitting diode according to an embodiment of the invention;

fig. 2 is a flowchart of a method for manufacturing an epitaxial wafer of a GaN-based light emitting diode according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the related art, the P-type GaN layer adopts N₂And H₂The mixed gas is used as a carrier gas, and because the P-type GaN layer needs to be doped with Mg highly to generate enough holes, the Mg has low solubility in GaN and is easy to form Mg-H complexes with H, and deep level acceptors caused by the complexes are used as hole traps to cause non-radiative recombination, so that the hole concentration is reduced. In addition, the H atomic mass is small, and the Mo (metal organic Source) brought in is little; the mass of N atoms is large, and much Mo is brought in. Mo is a high-purity metal organic compound material and is a raw material for metal organic chemical vapor phase epitaxy and deposition. When the amount of Mo introduced is small, the thickness of the P-type GaN layer is not high, and when the P-type GaN layer is too thin, the voltage of the LED chip is high.

Fig. 1 illustrates a method for preparing an epitaxial wafer of a GaN-based light emitting diode according to an embodiment of the invention. Referring to fig. 1, the process flow includes the following steps.

Step 101, providing a substrate.

Step 102, depositing a buffer layer, an undoped GaN layer, an N-type GaN layer, a defect barrier layer, a multi-quantum well layer, an electron barrier layer, a P-type GaN layer and a P-type contact layer on the substrate in sequence.

The P-type GaN layer comprises a first GaN sub-layer and a second GaN sub-layer. The first GaN sublayer is located between the electron blocking layer and the second GaN sublayer. When depositing the first GaN sub-layer, N is adopted₂And H₂The mixed gas of (2) as a carrier gas. When depositing the second GaN sub-layer, N is adopted₂As a carrier gas.

According to the embodiment of the invention, the P-type GaN layer comprises the first GaN sublayer and the second GaN sublayer, and N is adopted when the first GaN sublayer is deposited₂And H₂The mixed gas is used as a carrier gas, and N is adopted when the second GaN sub-layer is deposited₂As carrier gas, the first GaN sublayer is located between the electron blocking layer and the second GaN sublayer, so that the P-type GaN layer is divided into two sections for growth, and the second GaN sublayer, the later section, adopts only N₂As a carrier gas, H is reduced compared to a conventional P-type GaN layer₂The introduction of the compound reduces the formation of Mg-H compound, avoids non-radiative recombination caused by taking a deep energy level receptor caused by the Mg-H compound as a hole trap, and improves the hole concentration. At the same time, the latter section only adopts N₂As carrier gas, in pure N₂A smoother planar layer (namely a second GaN sublayer) is obtained in a high-temperature environment compared with the previous section, and V-shaped defects extending upwards from the MQW layer can be inhibited, so that the quality of grown crystals of the P-type GaN layer is higher, and the hole concentration is further improved.

Furthermore, the preceding segment, the first GaN sub-layer, employs N₂And H₂The mixed gas of (A) is used as a carrier gas, and the synthetic N is₂And H₂The amount of Mo brought in balances the thickness of the P-type GaN layer, and avoids the influence of the over-thickness of the P-type GaN layer on the brightness.

When the preceding section adopts N₂And H₂The mixed gas of (A) is used as carrier gas and only N is adopted in the next section₂When the carrier gas is combined, the average molecular density of the previous section is relatively low, which is beneficial to molecular motion and is beneficial to the hole to diffuse to the MQW layer as soon as possible; the crystal quality of the latter section is better, the concentration of the holes is higher than that of the former section, but the average molecular density is higher, and the diffusion speed of the holes is lower than that of the holes in the former section.

Fig. 2 shows a method for preparing an epitaxial wafer of a GaN-based light emitting diode according to an embodiment of the invention. Referring to fig. 2, the process flow includes the following steps.

Step 201, providing a substrate, and placing the substrate into a reaction chamber of an MOCVD device.

Illustratively, the Substrate may be PSS (Patterned Sapphire Substrate). PSS is on sapphire substrate (Al)₂O₃) Growing a mask for dry etching, etching a pattern on the mask by using a standard photoetching process, etching the sapphire by using an ICP (Inductively Coupled Plasma) etching technology, and removing the mask to form the sapphire substrate. And growing the GaN material on the PSS to change the longitudinal epitaxy of the GaN material into the transverse epitaxy. On one hand, the dislocation density of the GaN epitaxial material can be effectively reduced, so that the non-radiative recombination of an active region is reduced, the reverse leakage current is reduced, and the service life of the LED is prolonged; on the other hand, light emitted from the active region is scattered for multiple times through the interface of the GaN substrate and the sapphire substrate, so that the emergence angle of total reflection light is changed, the emergence probability of the light of the flip LED from the sapphire substrate is increased, and the light extraction efficiency is improved.

Specifically, the substrate is placed on a substrate tray in a reaction chamber of the MOCVD equipment, and the substrate tray is heated and driven to rotate. Illustratively, the substrate tray may be a graphite tray. As the substrate tray rotates, the substrate will rotate with the substrate tray.

In this embodiment, a GaN-based epitaxial layer on a substrate will be grown by the MOCVD method. In the MOCVD method, ammonia gas can be used as a nitrogen source, trimethyl gallium or triethyl gallium is used as a gallium source, trimethyl indium is used as an indium source, trimethyl aluminum is used as an aluminum source, silane is used as an N-type dopant, and magnesium cyclopentadienyl is used as a P-type dopant. It should be noted that the temperature and pressure controlled in the growth process described below actually refer to the temperature and pressure in the reaction chamber of the MOCVD equipment.

Step 202, the substrate is processed.

Wherein the substrate is treated to clean the surface of the substrate. Illustratively, the processing of the substrate includes: annealing for 8 minutes in a hydrogen atmosphere in the reaction cavity and keeping the temperature between 1000 ℃ and 1200 ℃.

Step 203, depositing a buffer layer on the substrate.

The buffer layer may be a GaN layer or an AlN layer. Taking the GaN layer as an example, the following growth method of the buffer layer is described, which includes: after the substrate is processed, the temperature of the reaction cavity is reduced to 400-600 ℃, the growth pressure is kept between 400Torr and 600Torr, and a low-temperature GaN buffer layer with the thickness of 15-35 nm is grown.

Illustratively, in growing the GaN buffer layer, N is employed₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂The flow rate of (A) may be 20 to 100L/min (liter per minute), H₂The flow rate of (A) may be 20 to 100L/min. NH as Nitrogen Source₃The flow rate of (A) may be 20 to 100L/min.

And step 204, annealing the buffer layer.

Wherein the annealing temperature is 1000-1200 ℃, the pressure range is 400-600 Torr, and the time is 5-10 minutes.

Illustratively, the atmosphere of the annealing treatment is N₂、H₂And NH₃Mixed gas of (2), N₂、H₂And NH₃The flow rate of the water is 20 to 100L/min.

Step 205, an undoped GaN layer is deposited on the buffer layer.

Illustratively, the undoped GaN layer is grown at a growth temperature of 1000 deg.C-1100 deg.C, a growth thickness of 1 to 5 μm, and a growth pressure of 100Torr to 500 Torr.

Illustratively, in growing the undoped GaN layer, N is employed₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂Flow rate and H₂The flow rate of the water is 20 to 100L/min. NH as Nitrogen Source₃The flow rate of (A) may be 20 to 100L/min.

Step 206, depositing an N-type GaN layer on the undoped GaN layer.

Illustratively, the thickness of the N-type GaN layer is between 1 and 5 micrometers, the growth temperature is between 1000 and 1200 ℃, and the growth pressure is between 100 and 500 Torr. The N-type GaN layer is doped with Si with the doping concentration of 10¹⁸cm^-3～10¹⁹cm^-3In the meantime.

Illustratively, in growing the N-type GaN layer, N is employed₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂Flow rate and H₂The flow rate of the water is 20 to 100L/min. NH as Nitrogen Source₃The flow rate of (A) may be 20 to 100L/min.

And step 207, depositing a defect blocking layer on the N-type GaN layer.

Wherein the defect blocking layer is used to block upwardly extending defects caused by the action of the underlying lattice-adapted stress. The defect blocking layer can be an N-type doped AlGaN sublayer, and the molar doping amount of Al can be 0-0.3. The thickness of the defect blocking layer can be 50-180 nm, the growth temperature can be 800-1100 ℃, and the growth pressure can be 300-500 Torr.

Illustratively, in growing the defect barrier layer, N is used₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂Flow rate and H₂The flow rate of the water is 20 to 100L/min. NH as Nitrogen Source₃The flow rate of (A) may be 20 to 100L/min.

And step 208, depositing a multi-quantum well layer on the defect barrier layer.

Wherein the MQW layer is 5 to 15 periods of In_aGa_1-aN(0<a<0.5) superlattice structure with alternately grown quantum wells and GaN quantum barriers. The thickness of the quantum well is about 3nm, the growth temperature range is 720-829 ℃, the pressure range is between 100Torr and 500 Torr: the thickness of the quantum barrier is between 9nm and 20nm, the growth temperature is between 850 ℃ and 959 ℃, and the growth pressure is between 100Torr and 500 Torr.

Illustratively, in growing the multiple quantum well layer, N is employed₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂The flow rate of (A) can be 20-100L/min, H₂The flow rate of (A) may be 0to 10L/min. NH as Nitrogen Source₃The flow rate of (A) may be 20 to 100L/min.

And step 209, depositing an electron barrier layer on the multi-quantum well layer.

Illustratively, the electron blocking layer is Al_xGa_1-xN(0.1<x<0.5) layer with a growth temperature between 850 ℃ and 1080 ℃, a growth pressure between 200Torr and 500Torr, and a growth thickness between 50nm and 150 nm.

Illustratively, in growing the electron blocking layer, N is used₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂Flow rate and H₂The flow rate of the water is 20 to 100L/min. NH as Nitrogen Source₃The flow rate of (A) may be 20 to 100L/min.

The electron blocking layer functions to block the overflow of electrons to some extent, and in addition, in this embodiment, the electron blocking layer can generate holes and increase the number of holes. Illustratively, the electron blocking layer is doped with Mg at a Mg doping concentration of 2X 10¹⁷～2×10¹⁸cm^-3. By doping the electron blocking layer with Mg, a certain number of holes can be generated, and the hole injection efficiency into the MQW region can be increased.

Step 210, depositing a P-type GaN layer on the electron blocking layer.

The P-type GaN layer comprises a first GaN sublayer and a second GaN sublayer, and the first GaN sublayer is located between the electron blocking layer and the second GaN sublayer. Illustratively, step 210 may include step a and step B.

And step A, depositing a first GaN sublayer on the electron blocking layer.

Wherein N is used in depositing the first GaN sublayer₂And H₂The mixed gas of (2) as a carrier gas. In a mixed gas, N₂And H₂The flow ratio of (1): 10-1: 2. preferably, N₂And H₂The flow ratio of (1): 10. by N₂Is much smaller than H₂Can be in a large amount of H₂Due to H, a first GaN sub-layer is grown under the atmosphere of₂Thermal conductivity ratio N of₂The temperature of the first GaN sublayer can therefore be adjusted to be lower than that of a conventional P-type GaN layer, which protects the MQW layer close to the first GaN sublayer.

Illustratively, in a mixed gas, N₂The flow rate of (A) is more than or equal to 20L/min, H₂The flow rate of (A) is less than or equal to 100L/min. Preferably, in the mixed gas, N₂The flow rate of (2) is 20L/min, H₂The flow rate of (2) is 100L/min.

Illustratively, the growth temperature of the first GaN sublayer is 900-1000 ℃, and the growth pressure of the first GaN sublayer and the second GaN sublayer is 100-300 Torr.

Illustratively, the thickness of the first GaN sublayer is 10-50 nm.

Illustratively, the first GaN sublayer is Mg-doped and has a Mg doping concentration of 10¹⁸～10¹⁹cm^-3。

And step B, depositing a second GaN sub-layer on the first GaN sub-layer.

Wherein N is used in depositing the second GaN sublayer₂As a carrier gas. Exemplarily, N₂The flow rate of (A) is 20 to 100L/min. Preferably, N₂The flow rate of (2) is 60L/min.

Illustratively, the growth temperature of the second GaN sublayer is 930-1050 ℃. The growth pressure of the first GaN sublayer and the second GaN sublayer is 100-300 Torr.

Illustratively, the thickness of the second GaN sublayer is 50-100 nm. The second GaN sublayer is thicker than the first GaN sublayer in consideration of the better crystal quality of the second GaN sublayer, the ability to provide a larger number of holes, and the ease of diffusion into the first GaN sublayer.

Illustratively, the second GaN sub-layer is doped with Mg with a Mg doping concentration higher than that of the first GaN sub-layer, for example, the Mg doping concentration of the second GaN sub-layer is 10²⁰～10²¹cm^-3. The Mg doping concentration in the second GaN sublayer is higher than that in the first GaN sublayer, so that the growing condition of the second GaN sublayer is considered to be easy for Mg to be incorporated, the crystal quality is good, a large number of holes can be provided, and the holes can be easily diffused to the first GaN sublayer.

And 211, depositing a P-type contact layer on the P-type GaN layer.

Illustratively, the P-type contact layer is a GaN or InGaN layer with a thickness of 5nm to 300nm, a growth temperature range of 850 ℃ to 1050 ℃, and a growth pressure range of 100Torr to 300 Torr.

Illustratively, in growing the P-type contact layer, N is used₂And H₂The mixed gas of (2) as a carrier gas. N is a radical of₂Flow rate and H₂The flow rate of the water is 20 to 100L/min. As nitrogen sourceNH of (2)₃The flow rate of (A) may be 20 to 100L/min.

Step 212, annealing the P-type contact layer.

Illustratively, after the growth of the P-type contact layer is finished, the temperature in a reaction cavity of the MOCVD equipment is reduced, annealing treatment is carried out in a nitrogen atmosphere, the annealing temperature is 700-800 ℃, the annealing treatment is carried out for 5-15 minutes, and the temperature is reduced to room temperature, so that the epitaxial growth is finished.

By the annealing temperature of 700-800 ℃ which is higher than the traditional annealing temperature, MgH bonds of MgH compounds formed in the first GaN sublayer can be opened, Mg doping is improved, and MgH passivation is reduced.

When the preceding section adopts N₂And H₂The mixed gas of (A) is used as carrier gas and only N is adopted in the next section₂When implemented as a carrier gas, the average molecular density of the preceding stage is relatively low, which is advantageousThe molecular motion is favorable for the holes to diffuse to the MQW layer as soon as possible; the crystal quality of the latter section is better, the concentration of the holes is higher than that of the former section, but the average molecular density is higher, and the diffusion speed of the holes is lower than that of the holes in the former section.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A preparation method of a GaN-based light emitting diode epitaxial wafer is characterized by comprising the following steps:

providing a substrate;

depositing a buffer layer, an undoped GaN layer, an N-type GaN layer, a defect barrier layer, a multi-quantum well layer, an electronic barrier layer, a P-type GaN layer and a P-type contact layer on the substrate in sequence, wherein the P-type GaN layer comprises a first GaN sublayer and a second GaN sublayer, the first GaN sublayer is positioned between the electronic barrier layer and the second GaN sublayer, and the N-type GaN layer is adopted during deposition of the first GaN sublayer₂And H₂The mixed gas is used as a carrier gas, and N is adopted when the second GaN sub-layer is deposited₂As a carrier gas;

the growth temperature of the first GaN sublayer is 900-1000 ℃, and the growth temperature of the second GaN sublayer is 930-1050 ℃;

in the mixed gas, N₂And H₂The flow ratio of (1): 10-1: 2 in the mixed gas, N₂The flow rate of (A) is more than or equal to 20L/min, H₂Is less than or equal to 100L/min, N is present during deposition of said second GaN sub-layer₂The flow rate of the first GaN sublayer and the second GaN sublayer is 20-100L/min, and the growth pressures of the first GaN sublayer and the second GaN sublayer are both100-300 Torr, the thickness of the first GaN sublayer is 10-50 nm, the thickness of the second GaN sublayer is 50-100 nm, Mg is doped in the first GaN sublayer and the second GaN sublayer, and the Mg doping concentration in the first GaN sublayer is 10¹⁸～10¹⁹cm^-3The Mg doping concentration in the second GaN sublayer is higher than that in the first GaN sublayer; the electron blocking layer is Al_xGa_1-xN layer, 0.1<x<0.5, the electron blocking layer is doped with Mg, and the doping concentration of Mg is 2 multiplied by 10¹⁷～2×10¹⁸cm^-3；

The multiple quantum well layer is 5 to 15 periods of In_aGa_1-aN(0<a<0.5) superlattice structure with alternately grown quantum wells and GaN quantum barriers.