CN105742416A - Preparation method for gallium nitride based LED epitaxial wafer with high light emitting efficiency - Google Patents

Abstract

The invention belongs to the field of optoelectronic devices, and in particular relates to a preparation method of gallium nitride-based LED epitaxial wafers with high luminous efficiency. The structure made by this method includes sequentially stacked low-temperature GaN nucleation layer, hollow GaN rough layer, non-doped GaN layer, N-type GaN layer, multi-quantum well active layer, electron blocking layer and P-type GaN layer. The growth of the GaN rough layer with hollow structure includes first growing the first 3D structure GaN layer, then treating the first 3D structure GaN layer with _H2 gas at high temperature, then growing the second 3D structure GaN layer, and finally growing the 3D structure GaN layer The fast merging of layers makes the holes evenly distributed in the process of merging islands. The present invention uses _H2 to process the 3D structure GaN layer, and the obtained GaN island structure is more uniform in size and spatial distribution, so that the cavities generated during the rapid merging process of the 3D structure GaN layer are also more uniform, and the hollow structure The GaN rough layer can reduce total internal reflection, which is beneficial to improve the light extraction efficiency of GaN-based LEDs.

Description

A preparation method of GaN-based LED epitaxial wafer with high luminous efficiency

technical field

The invention belongs to the field of optoelectronic devices, and in particular relates to a preparation method of gallium nitride-based LED epitaxial wafers with high luminous efficiency.

Background technique

Gallium nitride-based light-emitting diodes (LightEmittingDiode, LED) have the characteristics of high brightness, low energy consumption, long life, fast response and environmental protection, and are widely used in indoor and street lighting, traffic signals and outdoor displays, automotive lighting, LCD Backlight and many other fields. Therefore, high-power white LEDs are considered to be the lighting source of the 21st century.

In order to obtain high-brightness LEDs, the key is to improve the internal quantum efficiency and external quantum efficiency of the device. At present, the internal quantum efficiency of blue-light GaN-based LEDs can reach more than 80%, but the external quantum efficiency of high-power LED chips is usually only about 40%. The main factor that restricts the improvement of external quantum efficiency is the low light extraction efficiency of the chip, because the refractive index of GaN material (n=2.5) is different from that of air (n=1) and that of sapphire substrate (n=2.5). 1.75) is quite different, resulting in the critical angles of total reflection at the air-GaN interface and sapphire-GaN interface being only 23.6° and 44.4°, respectively, and only a small amount of light generated in the active region can escape from the bulk material. In order to improve the light extraction efficiency of the chip, the main technical solutions currently used at home and abroad include growth distributed Bragg reflector (DBR) structure, patterned substrate (PSS) technology, surface roughening technology and photonic crystal technology. PSS has high requirements on the regularity of the pattern, and the sapphire substrate is relatively hard. Whether it is dry etching or wet etching process, it is difficult to achieve the consistency and uniformity of the entire pattern, and the production process The requirements for equipment and process are very high, resulting in high cost. The manufacturing process of DBR and photonic crystal is relatively complex and costly, and the surface roughening technology adopts dry etching or wet etching process, which also presents great challenges.

Contents of the invention

The purpose of the present invention is to provide a method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency in view of the above-mentioned defects in the prior art, and the method is simple and the preparation cost is low.

The present invention is realized by adopting the following technical scheme: a method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency, comprising the following steps:

Step 1: clean the surface of the sapphire substrate in the hydrogen atmosphere of the reaction chamber, the temperature in the reaction chamber is 1060-1100°C, and the time is 5min-10min;

Step 2: Lower the temperature of the reaction chamber to 520-550°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 20-40nm, and the growth pressure is 400-700Torr;

Step 3: Raise the temperature of the reaction chamber to 950-1000° C. and keep it stable for 2 minutes to perform high-temperature annealing of the GaN nucleation layer. During this process, NH ₃ gas is introduced to prevent the complete decomposition of the GaN nucleation layer. Then the metal-organic source TMGa is introduced, and the GaN layer of the first 3D structure is grown on the surface of the GaN nucleation layer. The growth thickness is 200-300nm, and the growth pressure is 400-700Torr. islands and large GaN islands;

Step 4: Raise the temperature of the reaction chamber to 1030-1110°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas to process GaN with 3D structure for 5-10min. During this process, H ₂ gas will etch the GaN layer of the first 3D structure, small GaN islands will be etched away, and large GaN islands will remain. , small GaN islands and large GaN islands have no clear size definition, but small GaN islands are easily etched away during the etching process, so the etched GaN islands are small GaN islands, and the remaining ones The GaN island is a large GaN island;

Step 5: Lower the temperature of the reaction chamber to 950-1000°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a second 3D GaN layer of 500-1000nm on the 3D GaN layer after H ₂ gas treatment , the growth pressure is 400-700Torr, and the enlarged 3D structure GaN layer is obtained;

Step 6: Raise the temperature of the reaction chamber to 1050-1200°C, and rapidly grow undoped GaN on the enlarged 3D GaN layer, so that the 3D island structure heals quickly, and finally forms a relatively uniform internal cavity and a flat surface GaN rough layer with a hollow structure, the growth thickness is 1~2um, and the growth pressure is 50-300Torr;

Step 7: Grow an unintentionally doped GaN layer with a thickness of 1~2um, a growth temperature of 1050-1200°C, and a growth pressure of 50-300Torr;

Step 8: growing a Si-doped GaN layer with a carrier concentration of 10 ¹⁸ -10 ¹⁹ cm ^-3 , a thickness of 1-3um, a growth temperature of 1050-1200°C, and a growth pressure of 50-300 Torr;

Step 9: grow 3-6 periods of multi-quantum well active layer, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 10-30% by mass fraction, the thickness of the well layer is 2-5nm, and the temperature The temperature is 700-800°C, the thickness of the barrier layer is 8-13nm, the growth temperature is 800-950°C, and the pressure during the growth process is 200-500Torr;

Step 10: growing a p-AlGaN electron blocking layer with a thickness of 20-50 nm, the Al component in this layer is 10-20% by mass fraction, the hole concentration is 10 ¹⁷ -10 ¹⁸ cm ^-3 , and the growth temperature is 850°C -1000℃, the pressure is 50-300Torr;

Step eleven: growing a Mg-doped GaN layer with a thickness of 100-300 nm, a growth temperature of 850-1000°C, a growth pressure of 100-500 Torr, and a hole concentration of 10 ¹⁷ -10 ¹⁸ cm ^-3 ;

Step 12: After the epitaxial growth is completed, lower the temperature of the reaction chamber to 650-800° C., perform annealing treatment in a nitrogen atmosphere for 5-15 minutes, and then lower it to room temperature, and end the growth to obtain an epitaxial wafer.

The epitaxial growth process of the present invention is carried out in the MOCVD reaction chamber of the metal organic chemical vapor deposition process (MOCVD). layer, non-doped GaN layer, N-type GaN layer, multi-quantum well active layer, electron blocking layer, and P-type GaN layer. In the epitaxial growth process of the present invention, trimethylgallium (TMGa), triethylgallium (TEGa ), trimethylaluminum (TMAl), trimethylindium (TMIn) and ammonia (NH ₃ ) are Ga, Al, In and N sources respectively, silane (SiH ₄ ) and dimagnesocene (CP ₂ Mg) are N, P type dopant.

Through the above process, the present invention grows a hollow GaN rough layer with relatively uniform inner cavity and flat surface on the sapphire substrate. The GaN rough layer with hollow structure can reduce total internal reflection, which is beneficial to improve the light extraction efficiency of GaN-based LEDs. In addition, the two-step GaN3D structure growth process helps to change the growth direction of dislocations, reduces the dislocation density in the active region, and improves the crystal quality of the epitaxial wafer.

Description of drawings

Figure 1 is a flow chart of growing epitaxial wafers in the prior art, which sequentially grows a low-temperature GaN nucleation layer, non-doped GaN, N-type GaN, multi-quantum well active layer, electron blocking layer, and P-type GaN on a sapphire substrate. GaN layer.

Fig. 2 is a flow chart of growing an epitaxial wafer in the present invention, which sequentially stacks and grows a low-temperature GaN nucleation layer, a GaN layer with a first 3D structure, a GaN layer with a second 3D structure, and a fast process for growing a GaN layer with a 3D structure on a sapphire substrate. Merge layer, non-doped GaN, N-type GaN, multi-quantum well active layer, electron blocking layer, P-type GaN layer.

Fig. 3 is a schematic diagram after growing a GaN layer with a first 3D structure on the epitaxial wafer.

FIG. 4 is a schematic diagram after H ₂ high temperature treatment of the GaN layer of the first 3D structure.

FIG. 5 is a schematic diagram after growing a GaN layer of a second 3D structure.

FIG. 6 is a schematic diagram of voids formed inside after GaN layers with a 3D structure are rapidly merged.

Fig. 7 is a comparison diagram of light output power distribution of LED chips made by using the epitaxial wafer grown by the method provided by the present invention and the epitaxial wafer grown by the common method respectively.

detailed description

Embodiment one:

A method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency, comprising the following steps:

Step 1: clean the surface of the sapphire substrate in the hydrogen atmosphere of the MOCVD reaction chamber, the temperature in the reaction chamber is 1060 ° C, and the time is 10 minutes;

Step 2: Lower the temperature of the reaction chamber to 520°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 20nm, and the growth pressure is 400Torr;

Step 3: Raise the temperature of the reaction chamber to 950°C. During the heating process, NH ₃ gas is introduced to prevent the complete decomposition of the GaN nucleation layer, and then the metal-organic source TMGa is introduced to grow the first 3D structure on the surface of the GaN nucleation layer. GaN layer with a growth thickness of 200nm and a growth pressure of 400Torr, the GaN layer of the first 3D structure includes small GaN islands and large GaN islands;

Step 4: Raise the temperature of the reaction chamber to 1030°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas is introduced. The GaN layer of the first 3D structure is processed for 10 minutes. During this process, the _H2 gas will etch the GaN layer of the 3D structure. The small GaN islands in the GaN layer of the first 3D structure will be etched away, and the large GaN The island remains;

Step 5: Lower the temperature of the reaction chamber to 950°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a second 3D structure GaN layer of 500 nm on the 3D structure GaN layer after H ₂ gas treatment, and the growth pressure is 400Torr, get enlarged 3D structure GaN layer;

Step 6: Raise the temperature of the reaction chamber to 1050°C, and rapidly grow undoped GaN on the enlarged GaN layer of the 3D structure, so that the 3D island structure heals quickly, and finally forms a hollow with relatively uniform internal voids and a flat surface Structured GaN rough layer, the growth thickness is 1um, and the growth pressure is 50Torr;

Step 7: growing an unintentionally doped GaN layer with a thickness of 1um, a growth temperature of 1050°C, and a growth pressure of 50Torr;

Step 8: growing a Si-doped GaN layer with a carrier concentration of 10 ¹⁸ cm ^-3 , a thickness of 1 um, a growth temperature of 1050°C, and a growth pressure of 50 Torr;

Step 9: grow three periods of multi-quantum well active layers, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 30% by mass fraction, the thickness of the well layer is 2nm, and the growth temperature is 700°C. The layer thickness is 8nm, the growth temperature is 800°C, and the pressure during the growth process is 200Torr;

Step 10: growing a 20nm-thick p-AlGaN electron blocking layer, in which the Al component is 10% by mass fraction, the hole concentration is 10 ¹⁷ cm ^-3 , the growth temperature is 850°C, and the pressure is 50 Torr;

Step eleven: growing a Mg-doped GaN layer with a thickness of 100 nm, a growth temperature of 850°C, a growth pressure of 100 Torr, and a hole concentration of 10 ¹⁷ cm ^-3 ;

Step 12: After the epitaxial growth is completed, lower the temperature of the reaction chamber to 650°C, perform annealing treatment in a nitrogen atmosphere for 15 minutes, then lower it to room temperature, and end the growth to obtain an epitaxial wafer. The epitaxial wafer is cleaned, deposited, photolithography and After etching, a single small-sized chip is made.

Embodiment two:

A method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency, comprising the following steps:

Step 1: clean the surface of the sapphire substrate in the hydrogen atmosphere of the MOCVD reaction chamber, the temperature in the reaction chamber is 1100°C, and the time is 5 minutes;

Step 2: Lower the temperature of the reaction chamber to 550°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 40nm, and the growth pressure is 700Torr;

Step 3: Raise the temperature of the reaction chamber to 1000°C. During the heating process, NH ₃ gas is introduced to prevent the complete decomposition of the GaN nucleation layer, and then the metal-organic source TMGa is introduced to grow the first 3D structure on the surface of the GaN nucleation layer. GaN layer with a growth thickness of 300nm and a growth pressure of 700Torr, the GaN layer of the first 3D structure includes small GaN islands and large GaN islands;

Step 4: Raise the temperature of the reaction chamber to 1050°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas is introduced. The GaN layer with the first 3D structure is processed for 9 minutes. During this process, the _H2 gas will etch the GaN layer with the 3D structure. The small GaN islands in the GaN layer with the first 3D structure will be etched away, and the large GaN The island remains;

Step 5: Lower the temperature of the reaction chamber to 1000°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a second 3D structure GaN layer of 1000 nm on the 3D structure GaN layer after H ₂ gas treatment, and the growth pressure is 700Torr, get enlarged 3D structure GaN layer;

Step 6: Raise the temperature of the reaction chamber to 1200°C, and rapidly grow undoped GaN on the enlarged GaN layer of the 3D structure, so that the 3D island structure heals quickly, and finally forms a hollow with relatively uniform internal voids and a flat surface Structured GaN rough layer, the growth thickness is 2um, and the growth pressure is 300Torr;

Step 7: growing an unintentionally doped GaN layer with a thickness of 2um, a growth temperature of 1200°C, and a growth pressure of 300Torr;

Step 8: growing a Si-doped GaN layer with a carrier concentration of 10 ¹⁹ cm ^-3 , a thickness of 3um, a growth temperature of 1200°C, and a growth pressure of 300Torr;

Step 9: grow 4 periods of multi-quantum well active layers, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 10% by mass fraction, the thickness of the well layer is 5nm, the growth temperature is 800°C, and the barrier layer is The layer thickness is 13nm, the growth temperature is 950°C, and the pressure during the growth process is 500Torr;

Step 10: growing a p-AlGaN electron blocking layer with a thickness of 50 nm, the Al component in this layer is 20% by mass fraction, the hole concentration is 10 ¹⁸ cm ^-3 , the growth temperature is 1000°C, and the pressure is 300 Torr;

Step eleven: growing a Mg-doped GaN layer with a thickness of 300 nm, a growth temperature of 1000°C, a growth pressure of 500 Torr, and a hole concentration of 10 ¹⁸ cm ^-3 ;

Step 12: After the epitaxial growth is completed, lower the temperature of the reaction chamber to 800°C, perform annealing treatment in a nitrogen atmosphere for 5 minutes, then lower it to room temperature, and end the growth to obtain an epitaxial wafer. The epitaxial wafer is cleaned, deposited, photolithography and After etching, a single small-sized chip is made.

Embodiment three:

A method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency, comprising the following steps:

Step 1: clean the surface of the sapphire substrate in the hydrogen atmosphere of the MOCVD reaction chamber, the temperature in the reaction chamber is 1080 ° C, and the time is 7 minutes;

Step 2: Lower the temperature of the reaction chamber to 530°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 30nm, and the growth pressure is 500Torr;

Step 3: Raise the temperature of the reaction chamber to 960°C. During the heating process, NH ₃ gas is introduced to prevent the complete decomposition of the GaN nucleation layer, and then the metal-organic source TMGa is introduced to grow the first 3D structure on the surface of the GaN nucleation layer. GaN layer with a growth thickness of 220nm and a growth pressure of 500Torr, the GaN layer of the first 3D structure includes small GaN islands and large GaN islands;

Step 4: Raise the temperature of the reaction chamber to 1070°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas is introduced. The GaN layer with the first 3D structure is processed for 9 minutes. During this process, the _H2 gas will etch the GaN layer with the 3D structure. The small GaN islands in the GaN layer with the first 3D structure will be etched away, and the large GaN The island remains;

Step 5: Lower the temperature of the reaction chamber to 960°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a 3D GaN layer of 700 nm on the 3D GaN layer after H ₂ gas treatment, with a growth pressure of 500 Torr. Get enlarged 3D structure GaN layer;

Step 6: Raise the temperature of the reaction chamber to 1100°C, and rapidly grow undoped GaN on the enlarged GaN layer of the 3D structure, so that the 3D island structure heals quickly, and finally forms a hollow with relatively uniform internal voids and a flat surface Structured GaN rough layer, the growth thickness is 1.2um, and the growth pressure is 120Torr;

Step 7: grow an unintentionally doped GaN layer with a thickness of 1.2um, a growth temperature of 1100°C, and a growth pressure of 120Torr;

Step 8: growing a Si-doped GaN layer with a carrier concentration of 3×10 ¹⁸ cm ^-3 , a thickness of 2um, a growth temperature of 1100°C, and a growth pressure of 120 Torr;

Step 9: grow 5 periods of multi-quantum well active layers, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 25% by mass fraction, the thickness of the well layer is 3nm, the growth temperature is 730°C, and the barrier layer is The layer thickness is 10nm, the growth temperature is 850°C, and the pressure during the growth process is 300Torr;

Step 10: growing a p-AlGaN electron blocking layer with a thickness of 30nm, the Al component in this layer is 12% by mass fraction, the hole concentration is 2×10 ¹⁷ cm ^-3 , the growth temperature is 930°C, and the pressure is 120 Torr;

Step eleven: growing a Mg-doped GaN layer with a thickness of 200 nm, a growth temperature of 930°C, a growth pressure of 400 Torr, and a hole concentration of 3×10 ¹⁷ cm ^-3 ;

Step 12: After the epitaxial growth is completed, reduce the temperature of the reaction chamber to 700°C, perform annealing treatment in a nitrogen atmosphere for 12 minutes, then lower it to room temperature, and end the growth to obtain an epitaxial wafer. The epitaxial wafer is cleaned, deposited, photolithography and After etching, a single small-sized chip is made.

Embodiment four:

A method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency, comprising the following steps:

Step 1: clean the surface of the sapphire substrate in the hydrogen atmosphere of the MOCVD reaction chamber, the temperature in the reaction chamber is 1070°C, and the time is 8 minutes;

Step 2: Lower the temperature of the reaction chamber to 540°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 25nm, and the growth pressure is 600Torr;

Step 3: Raise the temperature of the reaction chamber to 970°C. During the heating process, NH ₃ gas is introduced to prevent the complete decomposition of the GaN nucleation layer, and then the metal-organic source TMGa is introduced to grow the first 3D structure on the surface of the GaN nucleation layer. GaN layer with a growth thickness of 240nm and a growth pressure of 600Torr, the GaN layer of the first 3D structure includes small GaN islands and large GaN islands;

Step 4: Raise the temperature of the reaction chamber to 1090°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas is introduced. The GaN layer with the first 3D structure is processed for 7 minutes. During this process, the _H2 gas will etch the GaN layer with the 3D structure. The small GaN islands in the GaN layer with the first 3D structure will be etched away, and the large GaN The island remains;

Step 5: Lower the temperature of the reaction chamber to 970°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a second 3D structure GaN layer of 800 nm on the 3D structure GaN layer after H ₂ gas treatment, and the growth pressure is 600Torr, get enlarged 3D structure GaN layer;

Step 6: Raise the temperature of the reaction chamber to 1150°C, and rapidly grow undoped GaN on the enlarged GaN layer of the 3D structure, so that the 3D island structure heals quickly, and finally forms a hollow with relatively uniform internal voids and a flat surface Structured GaN rough layer, the growth thickness is 1.4um, and the growth pressure is 190Torr;

Step 7: grow an unintentionally doped GaN layer with a thickness of 1.4um, a growth temperature of 1150°C, and a growth pressure of 190Torr;

Step 8: growing a Si-doped GaN layer with a carrier concentration of 5×10 ¹⁸ cm ^-3 , a thickness of 1.5um, a growth temperature of 1150°C, and a growth pressure of 190 Torr;

Step 9: grow six periods of multiple quantum well active layers, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 15% by mass fraction, the thickness of the well layer is 4nm, the growth temperature is 780°C, and the barrier layer is The layer thickness is 9nm, the growth temperature is 920°C, and the pressure during the growth process is 450Torr;

Step 10: growing a 40nm-thick p-AlGaN electron blocking layer, the Al component in this layer is 14% by mass fraction, the hole concentration is 5×10 ¹⁷ cm ^-3 , the growth temperature is 970°C, and the pressure is 190 Torr;

Step eleven: growing a Mg-doped GaN layer with a thickness of 260nm, a growth temperature of 970°C, a growth pressure of 300Torr, and a hole concentration of 8×10 ¹⁷ cm ^-3 ;

Step 12: After the epitaxial growth is completed, lower the temperature of the reaction chamber to 780°C, perform annealing treatment in a nitrogen atmosphere for 7 minutes, then lower it to room temperature, and end the growth to obtain an epitaxial wafer. The epitaxial wafer has been cleaned, deposited, photolithography and After etching, a single small-sized chip is made.

Embodiment five:

A method for preparing gallium nitride-based LED epitaxial wafers with high luminous efficiency, comprising the following steps:

Step 1: clean the surface of the sapphire substrate in the hydrogen atmosphere of the MOCVD reaction chamber, the temperature in the reaction chamber is 1090°C, and the time is 6 minutes;

Step 2: Lower the temperature of the reaction chamber to 545°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 35nm, and the growth pressure is 650Torr;

Step 3: Raise the temperature of the reaction chamber to 980°C. During the heating process, NH ₃ gas is introduced to prevent the complete decomposition of the GaN nucleation layer, and then the metal-organic source TMGa is introduced to grow the first 3D structure on the surface of the GaN nucleation layer. GaN layer with a growth thickness of 260nm and a growth pressure of 550Torr, the GaN layer of the first 3D structure includes small GaN islands and large GaN islands;

Step 4: Raise the temperature of the reaction chamber to 1110°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas is introduced. The GaN layer of the first 3D structure is processed for 5 minutes. During this process, the _H2 gas will etch the GaN layer of the 3D structure. The small GaN islands in the GaN layer of the first 3D structure will be etched away, and the large GaN The island remains;

Step 5: Lower the temperature of the reaction chamber to 980°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a second 3D structure GaN layer of 1000 nm on the 3D structure GaN layer after H ₂ gas treatment, and the growth pressure is 650Torr, get enlarged 3D structure GaN layer;

Step 6: Raise the temperature of the reaction chamber to 1080°C, and rapidly grow undoped GaN on the enlarged GaN layer of the 3D structure, so that the 3D island structure heals quickly, and finally forms a hollow with relatively uniform internal voids and a flat surface Structured GaN rough layer, the growth thickness is 1.6um, and the growth pressure is 260Torr;

Step 7: grow an unintentionally doped GaN layer with a thickness of 1.6um, a growth temperature of 1080°C, and a growth pressure of 260Torr;

Step 8: growing a Si-doped GaN layer with a carrier concentration of 7×10 ¹⁸ cm ^-3 , a thickness of 2.5um, a growth temperature of 1080°C, and a growth pressure of 260 Torr;

Step 9: grow 5 periods of multi-quantum well active layers, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 20% by mass fraction, the thickness of the well layer is 3nm, the growth temperature is 760°C, and the barrier layer is The layer thickness is 12nm, the growth temperature is 890°C, and the pressure during the growth process is 400Torr;

Step 10: growing a p-AlGaN electron blocking layer with a thickness of 30nm, the Al component in this layer is 16% by mass fraction, the hole concentration is 3×10 ¹⁷ cm ^-3 , the growth temperature is 950°C, and the pressure is 260 Torr;

Step eleven: growing a Mg-doped GaN layer with a thickness of 220 nm, a growth temperature of 950°C, a growth pressure of 200 Torr, and a hole concentration of 5×10 ¹⁷ cm ^-3 ;

Step 12: After the epitaxial growth is completed, lower the temperature of the reaction chamber to 750°C, perform annealing treatment in a nitrogen atmosphere for 10 minutes, then lower it to room temperature, and end the growth to obtain an epitaxial wafer. The epitaxial wafer is cleaned, deposited, photolithography and After etching, a single small-sized chip is made.

Figure 3-Figure 6 is a schematic diagram of the process of growing a hollow GaN rough layer in the present invention, wherein Figure 3 is a schematic diagram after growing a GaN layer with a first 3D structure on an epitaxial wafer, and it can be seen from Figure 3 that the size and distribution of GaN islands are different. Uniform; Fig. 4 is a schematic diagram of the first 3D GaN layer after H ₂ high temperature treatment. It can be seen from Fig. 4 that the small GaN islands are etched away by H ₂ , the number of islands becomes smaller and the size is more uniform; Fig. 5 shows the growth of the first 3D structure The schematic diagram after the GaN layer of the 23D structure, when GaN grows, it grows preferentially in the position with GaN islands, and grows slowly in other positions, and finally forms a GaN three-dimensional island structure with a larger size and a more uniform size and distribution. FIG. 6 is a schematic diagram of voids formed inside after GaN layers with a 3D structure are rapidly merged. The hollow GaN rough layer with relatively uniform internal cavity and flat surface can reduce total internal reflection and is beneficial to improve the light extraction efficiency of GaN-based LEDs. In addition, the two-step GaN3D structure growth process helps to change the growth direction of dislocations, reduces the dislocation density in the active region, and improves the crystal quality of the epitaxial wafer.

Fig. 7 is a comparison diagram of light output power distribution of LED chips made by using the epitaxial wafer grown by the method provided by the present invention and the epitaxial wafer grown by the common method respectively. The test condition is to randomly select 180 samples, the chip size is 8x10mil, and the test current is 20mA. The average light output power of the chip using the traditional method is 18.1mW, while the average light output power of the chip using the method provided by the present invention is 22.9mW, that is, the light output power of the chip grown by the method provided by the present invention is higher than that of the LED chip formed by the ordinary method. The output power has increased by about 26.5%.

Claims (1)

1. A preparation method of gallium nitride-based LED epitaxial wafer with high luminous efficiency, characterized in that it comprises the following steps: Step 1: Clean the substrate surface of the sapphire substrate in the hydrogen atmosphere of the reaction chamber, the temperature in the reaction chamber is 1060-1100°C, and the time is 5min-10min; Step 2: Lower the temperature of the reaction chamber to 520-550°C, and then grow a low-temperature GaN nucleation layer on the cleaned sapphire substrate, the thickness of the nucleation layer is 20-40nm, and the growth pressure is 400-700Torr; Step ₃ : Raise the temperature of the reaction chamber to 950-1000°C and stabilize it for 2 minutes to perform high-temperature annealing of the GaN nucleation layer. Source TMGa, start to grow the GaN layer of the first 3D structure on the surface of the GaN nucleation layer, the growth thickness is 200-300nm, the growth pressure is 400-700Torr, the GaN layer of the first 3D structure includes small GaN islands and large GaN island; Step 4: Raise the temperature of the reaction chamber to 1030-1110°C. During the heating process, NH ₃ gas is introduced to prevent the GaN layer of the first 3D structure from decomposing. After the heating is completed, the introduction of NH ₃ gas is turned off, and only H ₂ gas to process the GaN layer of the first 3D structure for 5-10min. During this process, the _H2 gas will etch the GaN layer of the 3D structure, and the small GaN islands in the GaN layer of the first 3D structure will be etched away , the large GaN islands are retained; Step 5: Lower the temperature of the reaction chamber to 950-1000°C, feed NH ₃ gas and metal-organic source TMGa, and continue to grow a second 3D GaN layer of 500-1000nm on the 3D GaN layer after H ₂ gas treatment , the growth pressure is 400-700Torr, and the enlarged 3D structure GaN layer is obtained; Step 6: Raise the temperature of the reaction chamber to 1050-1200°C, and rapidly grow undoped GaN on the enlarged 3D GaN layer, so that the 3D island structure heals quickly, and finally forms a relatively uniform internal cavity and a flat surface GaN rough layer with a hollow structure, the growth thickness is 1~2um, and the growth pressure is 50-300Torr; Step 7: Grow an unintentionally doped GaN layer with a thickness of 1~2um, a growth temperature of 1050-1200°C, and a growth pressure of 50-300Torr; Step 8: growing a Si-doped GaN layer with a carrier concentration of 10 ¹⁸ -10 ¹⁹ cm ^-3 , a thickness of 1-3um, a growth temperature of 1050-1200°C, and a growth pressure of 50-300 Torr; Step 9: grow 3-6 periods of multi-quantum well active layer, wherein the barrier layer is GaN, the well layer is InGaN, the In composition is 10-30% by mass fraction, and the thickness of the well layer is 2-5nm. The temperature is 700-800°C, the thickness of the barrier layer is 8-13nm, the growth temperature is 800-950°C, and the pressure during the growth process is 200-500Torr; Step 10: growing a p-AlGaN electron blocking layer with a thickness of 20-50 nm, the Al component in this layer is 10-20% by mass fraction, the hole concentration is 10 ¹⁷ -10 ¹⁸ cm ^-3 , and the growth temperature is 850°C -1000℃, pressure 50-300Torr,; Step eleven: growing a Mg-doped GaN layer with a thickness of 100-300 nm, a growth temperature of 850-1000°C, a growth pressure of 100-500 Torr, and a hole concentration of 10 ¹⁷ -10 ¹⁸ cm ^-3 ; Step 12: After the epitaxial growth is completed, lower the temperature of the reaction chamber to 650-800° C., perform annealing treatment in a nitrogen atmosphere for 5-15 minutes, and then lower it to room temperature, and end the growth to obtain an epitaxial wafer.