CN106159046A - A kind of LED epitaxial structure improving GaN crystal quality - Google Patents

Abstract

An LED epitaxial structure for improving GaN crystal quality relates to the field of light emitting diode epitaxial technology. The invention comprises a patterned substrate, a GaN buffer layer, a U-type GaN layer, an N-type GaN layer, an InGaN well layer, a GaN barrier layer, an electron blocking layer and a P-type GaN layer in order from bottom to top. Its structural feature is that the U-type GaN layer includes a U1-type GaN layer and a U2-type GaN layer from bottom to top. The U2-type GaN layer includes alternately grown 2D-type GaN layers and 3D-type GaN layers. Compared with the prior art, the invention can effectively reduce the spontaneous polarization and the piezoelectric polarization, increase the probability of radiation recombination, and thus achieve the purpose of enhancing the light extraction efficiency of the LED.

Description

An LED epitaxial structure with improved GaN crystal quality

technical field

The invention relates to the technical field of light-emitting diode epitaxy, in particular to an LED epitaxy structure capable of improving the quality of GaN crystals.

Background technique

GaN-based materials are direct bandgap semiconductors, and their bandgap is continuously adjustable from 1.8-6.2V. It is widely used in backlight, display screen, sensor, communication and lighting and other fields due to its long life, environmental protection and durability. Therefore, many LED experts and scholars are committed to the research and development of LED brightness, and the influence of epitaxial growth method on brightness is particularly important.

The radiation recombination efficiency is the key point of the epitaxial growth process affecting the brightness. There are many factors affecting it, such as quantum confinement effect, polarization effect, deep energy level caused by defects and impurities, which will reduce the radiation recombination efficiency. The defect density is the main factor affecting the internal quantum efficiency. During the growth process, due to the lattice mismatch and thermal mismatch between the substrate and the epitaxial layer, there are a large number of non-radiative defects inside the LED, and the dislocation density reaches 10 ⁹ cm ^-2 ~10 ¹¹ cm ⁻² . The resulting spontaneous polarization and piezoelectric effect lead to a strong built-in electric field, causing the wave functions of electrons and holes to be separated in spatial distribution, that is, the quantum-confined Stark effect QCSE, which reduces the luminous efficiency, and with As the injection current increases and the temperature of the device increases, the wavelength will drift and the luminous efficiency will also decrease, that is, the Droop phenomenon. Too many defects will also cause tunneling breakdown of the PN junction, which will greatly reduce the antistatic ability of the device and easily lead to device failure.

In the prior art, referring to FIG. 1 , the LED epitaxial structure is as follows from bottom to top: patterned substrate 1, GaN buffer layer 2, U1-type gallium nitride layer 3, N-type gallium nitride layer 4, and InGaN well layer 5 , GaN barrier layer 6, electron blocking layer 7 and P-type gallium nitride layer 8. The above conventional LED epitaxial wafer structure cannot effectively overcome the lattice mismatch between the patterned substrate 1 and the GaN material, resulting in spontaneous polarization and piezoelectric polarization. The energy band is seriously bent, which reduces the ability of the quantum well to confine carriers, resulting in a larger leakage current. Moreover, the bending of the energy band causes holes with a very low concentration to not be evenly distributed in the active region composed of the InGaN well layer 5 and the GaN barrier layer 6, thereby reducing the recombination probability and affecting the quality of GaN crystals.

Contents of the invention

In view of the deficiencies in the above prior art, the purpose of the present invention is to provide an LED epitaxial structure with improved GaN crystal quality. It can effectively reduce spontaneous polarization and piezoelectric polarization, and increase the probability of radiation recombination, thereby achieving the purpose of enhancing the light extraction efficiency of LEDs.

In order to achieve the above-mentioned purpose of the invention, the technical solution of the present invention is realized in the following manner:

An LED epitaxial structure that improves the quality of GaN crystals, which includes a patterned substrate, a GaN buffer layer, a U-type GaN layer, an N-type GaN layer, an InGaN well layer, a GaN barrier layer, an electron blocking layer, and a P-type GaN layer from bottom to top. GaN layer. Its structural feature is that the U-type GaN layer includes a U1-type GaN layer and a U2-type GaN layer from bottom to top. The U2-type GaN layer includes alternately grown 2D-type GaN layers and 3D-type GaN layers.

In the above LED epitaxial structure, the U2-type GaN layer is grown in a hydrogen-nitrogen mixed environment, and the growth period is 3-30 periods.

In the above-mentioned LED epitaxial structure, the 2D GaN layer in the U2 GaN layer grows first, and then the 3D GaN layer grows alternately.

In the above LED epitaxial structure, the growth temperature of the 2D-type GaN layer is 1050-1110°C, the thickness is 0.05-0.5um, and the growth pressure is 100-300torr; the growth temperature of the 3D-type GaN layer is 990-1050°C, and the growth thickness is 0.05-0.5um, the growth pressure is 400-650torr.

Due to the adoption of the above structure, the present invention uses 3D and 2D superlattice growth structures in the process of growing blue LEDs, so that the quality of the underlying GaN crystal grows better. The structure of the present invention can effectively reduce the spontaneous polarization and piezoelectric polarization caused by the lattice mismatch between the patterned substrate and the GaN material, increase the probability of radiation recombination, reduce the dislocation density, improve the quality of the GaN crystal, and achieve The purpose of enhancing the light output efficiency of LED.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

FIG. 1 is a schematic diagram of an LED epitaxial structure in the prior art;

Fig. 2 is the schematic diagram of LED epitaxial structure of the present invention;

FIG. 3 is a schematic diagram of the structure of U2-type GaN layer epitaxy in the present invention.

detailed description

Referring to Fig. 2 and Fig. 3, the present invention includes a patterned substrate 1, a GaN buffer layer 2, a U-type GaN layer, an N-type GaN layer 4, an InGaN well layer 5, a GaN barrier layer 6, and an electron blocking layer 7 from bottom to top. and a p-type GaN layer 8 . The U-type GaN layer includes a U1-type GaN layer 3 and a U2-type GaN layer 40 from bottom to top. The U2-type GaN layer 40 includes alternately grown 2D-type GaN layers 401 and 3D-type GaN layers 402 , wherein the 2D-type GaN layer 401 grows first, and then the 3D-type GaN layer 402 re-grows. The U2-type GaN layer 40 is grown in a hydrogen-nitrogen mixed environment, and the growth period is 3-30 periods. The growth temperature of the 2D type GaN layer 401 is 1050-1110°C, the thickness is 0.05-0.5um, and the growth pressure is 100-300torr; the growth temperature of the 3D type GaN402 layer is 990-1050°C, the growth thickness is 0.05-0.5um, and the growth pressure is 400-650torr.

The LED epitaxial structure provided by the present invention can effectively reduce the stress caused by lattice mismatch between the patterned substrate 1 and the GaN layer by growing the U2-type GaN layer 40 between the U1-type GaN layer 3 and the N-type GaN layer 4 , thereby reducing the generation of dislocations; and the U2-type GaN layer 40 can function as a mask layer, and the threading dislocation of the substrate terminates at the interface between the substrate and the U2-type GaN layer 40 and is blocked. The structure of the present invention can reduce the lattice defects caused by the lattice fit between the patterned substrate 1 and the epitaxial layer, promote the lateral growth of the epitaxial layer, reduce the epitaxial defect density to below the order of 10 ⁶ cm ^{- 2} , and improve the epitaxial layer quality.

Moreover, the present invention uses the U2-type GaN layer 40 grown between the U1-type GaN layer 3 and the N-type GaN layer 4 to achieve later lateral epitaxial growth, reduce defects, and effectively block partial dislocations from extending to the N-type GaN layer 4 or the light-emitting layer, and concentrate another part of the dislocations in the region of the U2-type GaN layer 40, which improves the crystal quality of the epitaxial wafer, thereby increasing the low dislocation area of the epitaxial layer, reducing the dislocation density, and effectively reducing the dislocation caused by the patterned substrate. The spontaneous polarization and piezoelectric polarization caused by the lattice mismatch between the bottom 1 and the GaN material can increase the recombination probability of the wave function in the active region and improve the brightness of the epitaxial wafer.

Embodiment one

The growth method of the LED epitaxial structure of the present invention is:

1) The device is baked at a high temperature in an MOCVD reactor to remove residual impurities on the surface of the patterned substrate 1 .

2) Slowly lower the temperature between 400-800°C, and grow a layer of GaN buffer layer 2 on the patterned substrate 1.

3) Raise the temperature rapidly, at 1000-1200°C, grow a U1-type GaN layer 3 on the GaN buffer layer 2, grow for 5-50min, and have a thickness of 0.5-5um.

4) Re-grow a U2-type GaN layer 40 on the U1-type GaN layer 3:

a) First grow a 2D-type GaN layer 401 at a growth temperature of 1050° C., a thickness of 0.05 μm, and a growth pressure of 100 torr;

b) Then grow the 3D GaN layer 402 by rapid cooling and pressurization, the growth temperature is 990°C, the growth thickness is 0.05um, and the growth pressure is 400torr;

c) The growth cycle of the U2-type GaN layer 40 for improving GaN crystal quality is 30 cycles.

5) N-type GaN layer 5 is grown at a growth temperature of 1000-1200°C and a growth thickness of 0.5-5um.

6) Growth active area:

First grow the In _X Ga _1-X N well layer 5 at a temperature of 500-900° C., a growth thickness of 3-5 nm, a growth pressure of 100-500 torr, and an In composition of 0<x<1. Then rapidly raise the temperature to 600-1000° C. to grow an N-type GaN barrier layer 6 with a thickness of 5-15 nm and a growth pressure of 100-500 torr. The In _X Ga _1-X N well layer 5 grows N-type and is doped with elements For Si, the doping concentration is 2x10 ¹⁷ -2x10 ¹⁸ cm ^{- 3} .

7) Grow the P-type Al _x Ga _1-x N electron blocking layer 7 at 700-900°C, the Al composition is 0<x<1, and the thickness is 50-500 angstroms.

8) Finally, a P-type GaN layer 8 is grown at a growth temperature of 850-1050°C, with a thickness of 2000-10000 angstroms and a Mg concentration of 5x10 ¹⁸ ~5x10 ²³ cm ^{- 3} .

Embodiment two

The growth method of the LED epitaxial structure of the present invention is:

1) The device is baked at a high temperature in an MOCVD reactor to remove residual impurities on the surface of the patterned substrate 1 .

2) Slowly lower the temperature between 400-800°C, and grow a layer of GaN buffer layer 2 on the patterned substrate 1.

3) Raise the temperature rapidly, at 1000-1200°C, grow a U1-type GaN layer 3 on the GaN buffer layer 2, grow for 5-50min, and have a thickness of 0.5-5um.

4) Re-grow a U2-type GaN layer 40 on the U1-type GaN layer 3:

a) First grow a 2D GaN layer 401 at a growth temperature of 1080°C, a thickness of 0.1um, and a growth pressure of 200torr;

b) Then grow the 3D GaN layer 402 by rapid cooling and pressurization, the growth temperature is 1020°C, the growth thickness is 0.1um, and the growth pressure is 500torr;

c) The growth cycle of the U2-type GaN layer 40 for improving GaN crystal quality is 15 cycles.

5) N-type GaN layer 4 is grown at a growth temperature of 1000-1200°C and a growth thickness of 0.5-5um.

6) Growth active area:

First grow the In _X Ga _1-X N well layer 5 at a temperature of 500-900° C., a growth thickness of 3-5 nm, a growth pressure of 100-500 torr, and an In composition of 0<x<1. Then rapidly raise the temperature to 600-1000° C. to grow an N-type GaN barrier layer 6 with a thickness of 5-15 nm and a growth pressure of 100-500 torr. The In _X Ga _1-X N well layer 5 grows N-type, and the doping element is Si, the doping concentration is 2x10 ¹⁷ -2x10 ¹⁸ cm ^{- 3} .

7) Grow the P-type Al _x Ga _1-x N electron blocking layer 7 at 700-900°C, the Al composition is 0<x<1, and the thickness is 50-500 angstroms.

8) Growing a P-type GaN layer 8 at a growth temperature of 850-1050°C, with a thickness of 2000-10000 angstroms, and a Mg concentration of 5x10 ¹⁸ ~5x10 ²³ cm ^{- 3} .

Embodiment Three

The growth method of the LED epitaxial structure of the present invention is:

1) The device is baked at a high temperature in an MOCVD reactor to remove residual impurities on the surface of the patterned substrate 1 .

2) Slowly lower the temperature between 400-800°C to grow a layer of GaN buffer layer 2.

3) Raise the temperature rapidly, between 1000-1200°C, grow a U1-type GaN layer 3 on the GaN buffer layer 2, grow for 5-50min, and have a thickness of 0.5-5um.

4) Growing U2-type GaN layer 40:

a) First grow a 2D GaN layer 401 at a growth temperature of 1110°C, a thickness of 0.5um, and a growth pressure of 300torr;

b) Then grow the 3D GaN layer 402 by rapid cooling and pressurization, the growth temperature is 1050°C, the growth thickness is 0.5um, and the growth pressure is 650torr;

c) The growth period of the U2-type GaN layer for improving GaN crystal quality is 3 periods.

5) N-type GaN layer 4 is grown at a growth temperature of 1000-1200°C and a growth thickness of 0.5-5um.

6) Growth active area:

First grow the In _X Ga _1-X N well layer 5 at a temperature of 500-900° C., a growth thickness of 3-5 nm, a growth pressure of 100-500 torr, and an In composition of 0<x<1. Then rapidly raise the temperature to 600-1000° C. to grow an N-type GaN barrier layer 6 with a thickness of 5-15 nm and a growth pressure of 100-500 torr. The In _X Ga _1-X N well layer 5 grows N-type, and the doping element is Si, the doping concentration is 2x10 ¹⁷ -2x10 ¹⁸ cm ^{- 3} .

7) Grow the P-type Al _x Ga _1-x N electron blocking layer 7 at 700-900°C, the Al composition is 0<x<1, and the thickness is 50-500 angstroms.

8) Growing a P-type GaN layer 8 at a growth temperature of 850-1050°C, with a thickness of 2000-10000 angstroms, and a Mg concentration of 5x10 ¹⁸ ~5x10 ²³ cm ^{- 3} .

The above is only a specific embodiment of the present invention, and is not limited to other implementations of the present invention. Any obvious modifications, replacements or improvements made within the technical route principles of the present invention shall belong to the present invention. within the scope of protection of the invention.

Claims (4)

1. An LED epitaxial structure that improves the quality of GaN crystals, which sequentially includes a patterned substrate (1), a GaN buffer layer (2), a U-type GaN layer, an N-type GaN layer (4), and an InGaN well layer from bottom to top (5), GaN barrier layer (6), electron blocking layer (7) and P-type GaN layer (8), characterized in that: the U-type GaN layer includes a U1-type GaN layer (3) and a U2-type GaN layer from bottom to top A GaN layer (40), the U2-type GaN layer (40) includes alternately grown 2D-type GaN layers (401) and 3D-type GaN layers (402). 2. The LED epitaxial structure for improving GaN crystal quality according to claim 1, characterized in that: the U2-type GaN layer (40) is grown in a hydrogen-nitrogen mixed environment, and the growth cycle is 3-30 cycles. 3. The LED epitaxial structure for improving GaN crystal quality according to claim 1 or 2, characterized in that: the 2D-type GaN layer (401) in the U2-type GaN layer (40) grows first, and then the 3D-type GaN layer (402) The pattern of regrowth alternates with growth. 4. The LED epitaxial structure for improving GaN crystal quality according to claim 3, characterized in that: the growth temperature of the 2D GaN layer (401) is 1050-1110°C, the thickness is 0.05-0.5um, and the growth pressure is 100 -300torr; the growth temperature of 3D type GaN (402) layer is 990-1050℃, the growth thickness is 0.05-0.5um, and the growth pressure is 400-650torr.