Epitaxial structure for reducing defect density of blue-green Micro LED and growth method

Abstract

The invention provides an epitaxial structure for reducing the defect density of a blue-green Micro LED and a growth method, and belongs to the technical field of semiconductors. Firstly, a PVD plated AlN film is recrystallized under the high-temperature pure hydrogen condition, the compactness of the PVD plated AlN film is improved, then NH3 is introduced in a pulse mode, the surface is repaired, and the flatness of atomic arrangement of the PVD plated AlN film is improved; secondly, the AlN layers with the thicknesses of 15 nm and 30 nm are deposited in MOCVD under two different conditions respectively, and the AlN layers with the higher quality and the more consistent trend can be obtained by matching different annealing conditions after the layers grow; and finally, growing a GaN epitaxial layer with the thickness of 2.5-3.0 microns through a specially designed three-step growth method. By adopting the synergistic growth mode, the defect density can be effectively reduced, and the quality of a Micro LED green and blue epitaxial GaN material crystal is improved, so that electric leakage is reduced, and the internal quantum efficiency of a light-emitting diode is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to an epitaxial structure and growth method for reducing the defect density of blue-green Micro LEDs. Background Technology

[0002] Gallium nitride (GaN) is a core material in third-generation semiconductors such as LEDs and power electronic devices. Due to the complex and costly fabrication process of GaN single-crystal substrates, epitaxial growth currently primarily utilizes heterogeneous substrates such as sapphire (Al₂O₃), silicon (Si), and silicon carbide (SiC). With the development of display technology, full-color displays have become the main direction for future display development, and Micro LED (micro-light-emitting diode) display technology is considered the ultimate solution for future displays, making it a key area of ​​focus for leading global nitride semiconductor companies.

[0003] Major domestic display manufacturers are also expanding their presence in the GaN-based LED epitaxial chip field. Examples include BOE's investment in HC SemiTek, Hisense's investment in GCL-Poly Optoelectronics, and TCL CSOT's acquisition of Fujian Zhaoyuan Optoelectronics. A typical Micro LED blue-green epitaxial structure, from bottom to top, includes: a substrate (sapphire, Si, or SiC), and sequentially grown layers of a buffer layer, an undoped u-GaN layer, a silicon-doped n-GaN layer, an InGaN active layer, an electron blocking layer (EBL), and a magnesium-doped p-GaN layer. Among these, sapphire substrates are currently the most widely used substrate material by LED epitaxial chip manufacturers due to their overall cost-effectiveness.

[0004] However, a significant lattice constant mismatch and thermal expansion coefficient mismatch exist between the sapphire substrate and the GaN epitaxial layer, causing the GaN material to experience substantial compressive stress from the substrate during growth. This compressive stress induces a high density of line defects (such as dislocations), thereby significantly increasing the defect density of the material. When this material is used to fabricate Micro LED blue-green light chips, these defects directly lead to a series of undesirable optoelectronic properties, such as low internal quantum efficiency, severe reverse leakage current, and poor electrostatic discharge (ESD) resistance, thus limiting the performance and reliability of Micro LEDs.

[0005] LED epitaxial chip production typically uses sapphire substrates. On this substrate, a buffer layer composed of materials such as AlN, AlGaN, or GaN is first grown. Traditional growth processes—that is, sequentially fabricating the buffer layer and the GaN epitaxial layer on the sapphire substrate—often result in lattice mismatch between the buffer layer and the sapphire substrate, leading to sparse, indistinct, and disordered distribution of initially formed islands. This, in turn, causes the subsequently grown GaN columnar crystals to lack consistent orientation. During the island merging stage, the morphology of the islands themselves (such as tilting, deflection, or twisting) and their quality defects induce a large number of screw dislocations, edge dislocations, and mixed dislocations in the GaN material. These linear defects continue to extend and penetrate the entire GaN structure during subsequent epitaxial growth, resulting in a high density of line defects in the final GaN film. When such GaN materials with high defect density are processed into LED chips, they exhibit a series of undesirable optoelectronic properties, including low quantum efficiency, significant leakage current, and weak electrostatic discharge (ESD) resistance.

[0006] Sidewall repair of patterned substrates: Some patents focus on the sidewall growth repair of sapphire PSS substrates, such as Sanan Optoelectronics PCT / CN2018 / 078653. On the PSS patterned sidewalls, the initial AlGaN defect layer is removed by alternating deposition and plasma etching to form a smooth sidewall epitaxial surface. However, the process is complex and the cost is increased. This solution introduces additional multiple plasma treatment steps before the mainstream MOCVD process, which significantly increases the process complexity and time cost, and may affect production efficiency and cost control. There is also a risk of contamination and the introduction of new interface problems.

[0007] Composite substrates and gradient buffer layers: Some patents focus on the design of composite substrates and buffer layers, such as Chongqing University's CN102157654B, which uses a double-sided concave sapphire substrate to enhance stress release and heat dissipation, and grows an AlGaN buffer layer with a gradient Al composition to smoothly transition the lattice. However, double-sided patterned substrates are difficult to process. Processing patterns on the back side of the substrate places higher demands on photolithography, etching, and cleaning processes, significantly increasing the manufacturing cost of the substrate itself. In addition, the growth control of the gradient buffer layer is demanding. Precisely controlling the continuous gradient of the Al composition requires an extremely stable MOCVD airflow and temperature system, resulting in a narrow process window and posing a challenge to the consistency of mass production.

[0008] Porous Buffer Layer: Jiangxi Zhaochi Semiconductor CN119342951A, designs a composite structure in an N-type GaN layer containing a porous low-temperature GaN layer and a porous AlGaN / GaN superlattice layer to filter and block the upward extension of dislocations. However, a drawback is the difficulty in controlling the uniformity of pore size and distribution. Precisely controlling the size, density, and three-dimensional distribution of pores during the epitaxial growth of porous structures is a major technical challenge, directly affecting the defect filtering effect and the crystal quality of subsequent epitaxial layers. Furthermore, it may affect the electrical properties of the material. Although the porous structure filters dislocations, the pores themselves may disrupt the continuity and conductivity of the material, especially affecting the lateral current expansion capability of the N-type layer. A balance needs to be struck between porosity and conductivity. Summary of the Invention

[0009] To address the aforementioned issues, this invention provides an epitaxial structure and growth method for reducing the defect density of blue-green Micro LEDs. A 10-15 nm AlN film is deposited on a sapphire substrate using PVD. The AlN-coated substrate undergoes low-pressure, low-speed, high-temperature, pure hydrogen (H2) treatment in MOCVD to recrystallize the AlN film. During this process, the AlN thickness is reduced by approximately 10-15%, improving its density. Subsequently, while maintaining the same conditions, ammonia gas is introduced in a pulsed manner to repair the surface of the recrystallized AlN film, increasing its atomic arrangement flatness; this layer is defined as the first AlN layer. The temperature is then lowered from the high temperature to 800-820°C, with an N2 to NH3 ratio of 3:1, and no H2 is introduced, to deposit a low-temperature AlN layer of approximately 12-18 nm. The temperature is then raised to 1050°C for 3 minutes to anneal the AlN layer, improving its crystal quality; this layer is defined as the second AlN layer. Finally, the temperature is raised to 1100°C to grow a 26-35 nm thick high-temperature, low-pressure pulsed AlN layer. Its core objective is to obtain an AlN layer with higher crystal quality and more uniform crystal orientation, laying a solid foundation for subsequent GaN epitaxy, which is defined as the third AlN layer; finally, the GaN layer is grown through a three-step growth method; effectively reducing defect density, improving the crystal quality of GaN material for green and blue epitaxial growth of Micro LED, thereby reducing leakage current and improving the internal quantum efficiency of the light-emitting diode.

[0010] This invention is achieved through the following technical solution:

[0011] An epitaxial structure for reducing the defect density of blue-green Micro LEDs includes, from bottom to top, a substrate 100, a first AlN layer 200, an AlN buffer layer 300, and a three-step GaN layer 400. The AlN buffer layer 300 includes a second AlN layer 301 and a third AlN layer 302. The three-step GaN layer 400 includes a first GaN layer 401, a second GaN layer 402, and a third GaN layer 403. The second AlN layer 301 is a low-temperature AlN layer, and the third AlN layer 302 is a high-temperature, low-pressure pulsed AlN layer. The first GaN layer 401 is a lateral growth layer, the second GaN layer 402 is a growth enhancement layer, and the third GaN layer 403 is a gap-filling layer between the GaN layer and the PSS (Position Separator).

[0012] Preferably, the thickness of the first AlN layer 200 is 10~15nm.

[0013] Preferably, the second AlN layer 301 is a low-temperature AlN layer with a thickness of 12-18 nm, and the third AlN layer 302 is a high-temperature low-pressure pulsed AlN layer with a thickness of 26-35 nm.

[0014] Preferably, the second AlN layer 301 is a 15nm thick low-temperature AlN layer, and the third AlN layer 302 is a 30nm thick high-temperature low-pressure pulsed AlN layer.

[0015] Preferably, the thickness of the GaN layer 400 grown in the three-step method is 2.5-3.0 micrometers.

[0016] Preferably, the three-step growth GaN layer 400 is further provided with an n-type GaN layer 500, a V-shaped pit forming layer 600, an MQW light-emitting layer 700, a low-temperature PGaN layer 800, an electron blocking layer 900, and a high-temperature PGaN layer 1000, arranged sequentially from bottom to top.

[0017] An epitaxial structure growth method for reducing defect density in blue-green Micro LEDs includes the following steps:

[0018] Step 1: Preparation of the first AlN layer. The AlN film substrate for blue-green Micro LEDs is subjected to low-pressure, low-speed, high-temperature, pure hydrogen treatment in an MOCVD (AMEC Unimax model). The reaction chamber pressure is 50~100 Torr, the rotation speed is 500~700 RPM, the temperature is 1120℃~1150℃, the H2 flow rate is 340~380 L / min, and the N2 / NH3 ratio is set to 0, maintained for 10~15 min. Then, while maintaining the same conditions, ammonia gas is introduced in a pulsed manner, with NH3 set to 5L for 7 seconds and NH3 set to 0L for 5 seconds, and this cycle is repeated 30~50 times. The low-pressure, low-speed, high-temperature pure hydrogen treatment of the AlN film causes it to recrystallize, improving the density of the AlN layer. The pulsed ammonia gas is then introduced to repair the surface of the recrystallized AlN film, increasing the flatness of its atomic arrangement.

[0019] Step 2: Prepare the second AlN layer. After the first AlN layer is completed, reduce the temperature from 1120℃~1150℃ to 800℃~820℃, use a N2 to NH3 ratio of 5:2, do not pass H2, pass NH3 at a rate of 80~90 L / min for 40~60 seconds, and use a TMAl flow rate of 78~118 μmol / min to deposit a 12-18 nm low-temperature AlN layer. Then, raise the temperature to 1050℃ over 3 minutes to anneal the AlN layer and improve its crystal quality.

[0020] Step 3: Prepare the third AlN layer. After the second AlN layer is completed, raise the temperature to 1100℃ to grow a 26-35nm thick high-temperature low-pressure pulsed AlN layer. The growth conditions are: temperature 1100℃, pressure 150 Torr, N2 to NH3 ratio 1:2, no H2 flow, NH3 flow rate 180~200L / min.

[0021] Step 4: Prepare a three-step GaN layer, comprising three sub-layers. The first GaN layer is a lateral growth layer. The growth pressure for this stage is 150 torr~200 torr, the growth speed is 600rpm~750rpm, the growth temperature is 1030~1050℃, the H2:NH3 ratio is 9:1, the NH3 concentration is 40~50 L / min, N2 is set to 0, and the growth time is 30 seconds~5 minutes. The second GaN layer is a longitudinal growth layer. In this stage, the longitudinal growth rate is greater than the lateral growth rate, and the GaN layer height is approximately equal to the PSS height. The pressure and speed are the same as the first stage, the growth temperature is 1070~1090℃, the H2:NH3 ratio is 6:1, and the NH3 concentration is 45~55 L / min. The growth rate was set to L / min, N2 was 0, and the growth time was 8-15 minutes. The third GaN layer was the gap-filling layer between the GaN layer and PSS. The pressure and rotation speed in this section were the same as in the first section. The growth temperature was 1110-1130℃, N2 was 0, H2:NH3 = 5:1, and NH3 was between 60-70 L / min. The growth time was 5-8 minutes. The TMGa ratio of the three sections was 1:2:2.5, with the first section containing 5.52×10 L / min TMGa. -3 ~ 7.73×10 -3 mol / min;

[0022] Step 5: On the GaN layer grown by the three-step growth method, an n-type GaN layer 500, a V-shaped pit forming layer 600, an MQW light-emitting layer 700, a low-temperature PGaN layer 800, an electron blocking layer 900, and a high-temperature PGaN layer 1000 are grown sequentially from bottom to top.

[0023] Preferably, the pulsed growth method in step three employs the following four-step growth process: Step 1: TMAl (aluminum source) pulse injection, where only TMAl and carrier gas N2 are introduced, and NH3 is not introduced. At this time, the TMAl introduction rate is 31.5~47 μmol / min, where it undergoes pyrolysis and adsorption on the high-temperature substrate surface to form an aluminum atom layer or aluminum-containing intermediates, preparing for subsequent reactions; Step 2: Purge, where TMAl is turned off and only carrier gas N2 is introduced. The purpose of this step is to remove unadsorbed TMAl and byproducts in the reaction chamber, preventing them from pre-reacting with the nitrogen source in the gas phase, ensuring that growth is mainly carried out through surface reactions; Step 3: NH3 (nitrogen source) pulse injection, where NH3 and carrier gas N2 are introduced to react with the aluminum species already adsorbed on the substrate surface, generating an AlN monolayer; Step 4: Purge, where NH3 is turned off again and carrier gas N2 is introduced for purging to remove excess NH3 and reaction byproducts; The above four steps constitute one cycle, with the time for each step being 5, 3, 5, and 3 seconds, respectively, and the entire cycle is repeated 40-60 times. Its core objective is to enhance surface migration during the single-pulse stage of the metal source (TMAl), allowing aluminum atoms / molecules more time and energy to migrate to the lowest energy positions on the substrate surface, resulting in a more regular and consistent arrangement. This enables precise layer control and a quasi-atomic layer epitaxy mode, facilitating atomic-level interface control and thickness uniformity. This lays a solid foundation for subsequent GaN epitaxy. The growth of the high-temperature, low-pressure pulsed AlN layer effectively optimizes the orientation, density, and quality of AlN nuclei on the PSS, thereby reducing dislocation defects in the subsequent GaN epitaxial layer and ultimately improving the optoelectronic performance and reliability of the LED chip.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention employs high-temperature pure hydrogen conditions to recrystallize PVD-deposited AlN films, improving their density. Subsequently, NH3 is introduced in a pulsed manner to repair the surface and increase the flatness of the atomic arrangement. Next, AlN layers of 15 nm and 30 nm thickness are deposited under two different conditions in MOCVD. Different annealing conditions after each layer growth result in higher quality and more uniform AlN layers. Finally, a GaN epitaxial layer of 2.5–3.0 micrometers thickness is grown using a specially designed three-step growth method. This synergistic growth approach effectively reduces defect density, improves the crystal quality of green and blue epitaxial GaN materials for Micro LEDs, thereby reducing leakage current and improving the internal quantum efficiency of the light-emitting diode. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the present invention;

[0027] Figure 2 This is a SEM image of the first GaN layer of the present invention;

[0028] Figure 3 This is a SEM image of the second GaN layer of the present invention;

[0029] Figure 4 This is a SEM image of the third GaN layer of this invention.

[0030] In the figure: 100, substrate; 200, first AlN layer; 300, AlN buffer layer; 301, second AlN layer; 302, third AlN layer; 400, GaN layer; 401, first GaN layer; 402, second GaN layer; 403, third GaN layer; 500, n-type GaN layer; 600, V-shaped pit forming layer; 700, MQW light-emitting layer; 800, low-temperature PGaN layer; 900, electron blocking layer; 1000, high-temperature PGaN layer. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0032] Example

[0033] As per the instruction manual Figure 1 As shown, an epitaxial structure for reducing the defect density of blue-green Micro LEDs includes, from bottom to top, a substrate 100, a first AlN layer 200, an AlN buffer layer 300, and a three-step GaN layer 400. The AlN buffer layer 300 includes a second AlN layer 301 and a third AlN layer 302. The three-step GaN layer 400 includes a first GaN layer 401, a second GaN layer 402, and a third GaN layer 403. The second AlN layer 301 is a low-temperature AlN layer, the third AlN layer 302 is a high-temperature, low-pressure pulsed AlN layer, the first GaN layer 401 is a lateral growth layer, the second GaN layer 402 is a growth enhancement layer, and the third GaN layer 403 is a gap-filling layer between the GaN layer and the PSS (Pressure Separator). The first AlN layer 200 has a film thickness of 15 nm, the second AlN layer 301 is a 15 nm thick low-temperature AlN layer, and the third AlN layer 302 is a 30 nm thick high-temperature, low-pressure pulsed AlN layer.

[0034] In addition, above the GaN layer 400 grown by the three-step method, from bottom to top, there are also an n-type GaN layer 500, a V-shaped pit forming layer 600, an MQW light-emitting layer 700, a low-temperature PGaN layer 800, an electron blocking layer 900, and a high-temperature PGaN layer 1000.

[0035] An epitaxial structure growth method for reducing defect density in blue-green Micro LEDs includes the following steps:

[0036] Step 1: Preparation of the first AlN layer. The AlN film substrate for blue-green Micro LEDs is subjected to low-pressure, low-speed, high-temperature, pure hydrogen treatment in an MOCVD (AMEC Unimax model). The reaction chamber pressure is 50~100 Torr, the rotation speed is 500~700 RPM, the temperature is 1120℃~1150℃, the H2 flow rate is 340~380 L / min, and the N2 / NH3 ratio is set to 0, maintained for 10~15 min. Then, while maintaining the same conditions, ammonia gas is introduced in a pulsed manner, with NH3 set to 5L for 7 seconds and NH3 set to 0L for 5 seconds, and this cycle is repeated 30~50 times. The low-pressure, low-speed, high-temperature pure hydrogen treatment of the AlN film causes it to recrystallize, improving the density of the AlN layer. The pulsed ammonia gas is then introduced to repair the surface of the recrystallized AlN film, increasing the flatness of its atomic arrangement.

[0037] Step 2: Prepare the second AlN layer. After the first AlN layer is completed, reduce the temperature from 1120℃~1150℃ to 800℃~820℃, use a N2 to NH3 ratio of 5:2, do not pass H2, pass NH3 at a rate of 80~90 L / min for 40~60 seconds, and use a TMAl flow rate of 78~118 μmol / min to deposit a 15 nm low-temperature AlN layer. Then, raise the temperature to 1050℃ over 3 minutes to anneal the AlN layer and improve its crystal quality.

[0038] Step 3: Preparation of the third AlN layer. After the second AlN layer is completed, the temperature is raised to 1100℃ to grow a 30nm thick high-temperature, low-pressure pulsed AlN layer. The growth conditions are: temperature 1100℃, pressure 150 Torr, N2 to NH3 ratio 1:2, no H2 flow, NH3 flow rate 180~200 L / min. The pulsed growth method uses the following four steps: Step 1: TMAl (aluminum source) pulse injection, only TMAl and carrier gas N2 are introduced, NH3 is not introduced. At this time, the TMAl flow rate is 31.5~47 μmol / min. It undergoes pyrolysis and adsorption on the surface of the high-temperature substrate to form an aluminum atom layer or aluminum-containing intermediates, preparing for subsequent reactions; Step 2: Purging, TMAl is turned off, only carrier gas N2 is introduced. The purpose of this step is to remove unadsorbed substances in the reaction chamber. The first step involves removing attached TMAl and byproducts to prevent pre-reaction with the nitrogen source in the gas phase, ensuring that growth primarily occurs through surface reactions. The second step involves pulsed NH3 (nitrogen source) injection, introducing NH3 and carrier gas N2 to react with the aluminum species already adsorbed on the substrate surface, generating an AlN monolayer. The third step involves purging, where NH3 is shut off again, and carrier gas N2 is introduced to remove excess NH3 and reaction byproducts. These four steps constitute one cycle, with each step lasting 5, 3, 5, and 3 seconds, respectively, repeated 40-60 times. The core objective is to enhance surface migration during the single-pulse phase of the metal source (TMAl), allowing aluminum atoms / molecules more time and energy to migrate to the lowest energy positions on the substrate surface, resulting in a more regular and consistent arrangement. This achieves precise layer control and a quasi-atomic layer epitaxial mode, facilitating atomic-level interface control and thickness uniformity. This lays a solid foundation for subsequent GaN epitaxy. The growth of high-temperature, low-pressure pulsed AlN layers can effectively optimize the orientation, density, and quality of AlN nuclei on PSS, thereby reducing dislocation defects in subsequent GaN epitaxial layers and ultimately improving the photoelectric performance and reliability of LED chips.

[0039] Step 4: Prepare a three-step GaN layer, comprising three sub-layers. The first GaN layer is a lateral growth layer. The growth pressure for this stage is 150 torr~200 torr, the growth speed is 600rpm~750rpm, the growth temperature is 1030~1050℃, the H2:NH3 ratio is 9:1, the NH3 concentration is 40~50 L / min, N2 is set to 0, and the growth time is 30 seconds~5 minutes. The second GaN layer is a longitudinal growth layer. In this stage, the longitudinal growth rate is greater than the lateral growth rate, and the GaN layer height is approximately equal to the PSS height. The pressure and speed are the same as the first stage, the growth temperature is 1070~1090℃, the H2:NH3 ratio is 6:1, and the NH3 concentration is 45~55 L / min. The growth rate was set to L / min, N2 was 0, and the growth time was 8-15 minutes. The third GaN layer was the gap-filling layer between the GaN layer and PSS. The pressure and rotation speed in this section were the same as in the first section. The growth temperature was 1110-1130℃, N2 was 0, H2:NH3 = 5:1, and NH3 was between 60-70 L / min. The growth time was 5-8 minutes. The TMGa ratio of the three sections was 1:2:2.5, with the first section containing 5.52×10 L / min TMGa. -3 ~ 7.73×10 -3 mol / min.

[0040] like Figures 2 to 4 As shown in the SEM images of the first GaN layer, the second GaN layer, and the third GaN layer in the embodiment, Figure 2 The whitish area is the first GaN layer, which mainly grows in the gaps between PSS packs. In the early stage, this layer grows laterally with the AlN crystal islands as the center. As the crystal islands gradually grow larger and merge, the white area in the figure can be seen to be basically the same color, indicating that there is no obvious boundary after the crystal islands are healed, which is conducive to further reducing the defect density. Figure 3 Except for the black voids, the rest of the area is the second GaN layer. After the first GaN layer is merged, the GaN layer begins to grow vertically, and the film thickness gradually increases until it exceeds the height of the PSS. Figure 4 The GaN epitaxial layer has healed, and the main growth region of the third GaN layer is... Figure 3 The black area in the text.

[0041] Step 5: On the three-step GaN layer, from bottom to top, grow an n-type GaN layer 500, a V-shaped pit forming layer 600, an MQW light-emitting layer 700, a low-temperature PGaN layer 800, an electron blocking layer 900, and a high-temperature PGaN layer 1000. Specifically: n-type GaN layer 500: growth temperature 1090~1105℃, thickness 1.3~1.5 μm, Si concentration 1.5 E19~4 E19 Atom / cm3; V-shaped pit forming layer 600: growth temperature 860~900℃, thickness 0.3~0.4 μm, growth pressure 200~250 Torr; MQW emitting layer 700: growth 9~11 cycles, thickness 14~16 nm per cycle; Low-temperature PGaN layer 800: growth temperature 720~750℃, thickness 30~40 nm, Mg doping concentration 1E20~1.5E20 Atom / cm3; Electron blocking layer 900: growth 5~10 cycles, growth temperature 950~980℃, thickness 60~90 nm; High-temperature PGaN layer 1000: growth temperature 950~980℃, thickness 0.25~0.35 μm, Mg doping concentration 2E19~3E19 Atom / cm3. 3 .

[0042] The design mechanism of this invention is as follows: A 10-15 nm AlN film is deposited on the substrate using PVD. Then, it undergoes low-pressure, low-speed, high-temperature, pure hydrogen treatment in MOCVD to recrystallize the AlN film and improve its density. Ammonia (NH3) is introduced in a pulsed manner to repair the surface of the recrystallized AlN film, increasing the flatness of its atomic arrangement. Under specific atmospheric conditions (800℃-820℃), a 15 nm AlN layer is deposited. This is followed by a 3-minute annealing treatment at 1050℃ to improve crystal quality. A 30 nm thick pulsed AlN layer is deposited under high temperature and low pressure to obtain AlN nuclei with higher crystal quality and greater uniformity. Finally, a GaN layer is grown using a three-step growth method. This synergistic growth approach effectively reduces defect density, improves the crystal quality of the green and blue epitaxial GaN material for Micro LEDs, reduces leakage current, and enhances the internal quantum efficiency of the light-emitting diode.

[0043] The test data of the example was compared with that of the base example, and the test results are shown in the table below:

[0044]

[0045] Analysis of the table data shows that the XRD data indicates that the material in the example has high crystal quality, more complete crystallization, and larger grain size. The blue and green light brightness of the example is higher than that of the base, and the increase in blue light brightness is more significant, indicating that the luminescent performance of the material in the example is better.

[0046] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An epitaxial structure for reducing defect density in blue-green Micro LEDs, characterized in that: From bottom to top, the structure includes a substrate (100), a first AlN layer (200), an AlN buffer layer (300), and a three-step GaN layer (400). The AlN buffer layer (300) includes a second AlN layer (301) and a third AlN layer (302). The three-step GaN layer (400) includes a first GaN layer (401), a second GaN layer (402), and a third GaN layer (403). The second AlN layer (301) is a low-temperature AlN layer, and the third AlN layer (302) is a high-temperature, low-pressure pulsed AlN layer. The first GaN layer (401) is a lateral growth layer, the second GaN layer (402) is a growth layer, and the third GaN layer (403) is a gap-filling layer between the GaN layer and the PSS.

2. The epitaxial structure for reducing defect density in blue-green Micro LEDs according to claim 1, characterized in that: The thickness of the first AlN layer (200) is 10~15nm.

3. The epitaxial structure for reducing defect density in blue-green Micro LEDs according to claim 1, characterized in that: The second AlN layer (301) is a low-temperature AlN layer with a thickness of 12-18 nm, and the third AlN layer (302) is a high-temperature low-pressure pulsed AlN layer with a thickness of 26-35 nm.

4. The epitaxial structure for reducing defect density in blue-green Micro LEDs according to claim 1, characterized in that: The thickness of the GaN layer (400) grown by the three-step method is 2.5-3.0 micrometers.

5. The epitaxial structure for reducing defect density in blue-green Micro LEDs according to claim 1, characterized in that: Above the three-step growth GaN layer (400), from bottom to top, there are also an n-type GaN layer (500), a V-shaped pit forming layer (600), an MQW light-emitting layer (700), a low-temperature PGaN layer (800), an electron blocking layer (900), and a high-temperature PGaN layer (1000).

6. A method for growing an epitaxial structure to reduce the defect density of blue-green Micro LEDs, used to grow the epitaxial structure according to any one of claims 1 to 4, characterized in that: Includes the following steps: Step 1: Preparation of the first AlN layer. The AlN film-coated substrate for blue-green Micro LEDs is subjected to low-pressure, low-speed, high-temperature, and pure hydrogen treatment in MOCVD. The reaction chamber pressure is 50~100 Torr, the speed is 500~700 RPM, the temperature is 1120℃~1150℃, the H2 flow rate is 340~380 L / min, and the N2 / NH3 ratio is set to 0, which is maintained for 10~15 min. Then, while maintaining the same conditions, ammonia gas is introduced in a pulsed manner, with NH3 set to 5 L for 7 seconds and NH3 set to 0 L for 5 seconds, and this cycle is repeated 30~50 times. Step 2: Prepare the second AlN layer. After the first AlN layer is completed, reduce the temperature from 1120℃~1150℃ to 800℃~820℃, use a N2 to NH3 ratio of 5:2, do not pass H2, pass NH3 at a rate of 80~90 L / min for 40~60 seconds, and use a TMAl flow rate of 78~118 μmol / min to deposit a 12-18 nm low-temperature AlN layer. Then, raise the temperature to 1050℃ over 3 minutes to anneal the AlN layer and improve its crystal quality. Step 3: Prepare the third AlN layer. After the second AlN layer is completed, raise the temperature to 1100℃ to grow a 26-35nm thick high-temperature low-pressure pulsed AlN layer. The growth conditions are: temperature 1100℃, pressure 150 Torr, N2 to NH3 ratio 1:2, no H2 flow, NH3 flow rate 180~200L / min. Step 4: Prepare a three-step GaN layer, comprising three sub-layers. The first GaN layer is a lateral growth layer. The growth pressure for this stage is 150 torr~200 torr, the growth speed is 600rpm~750rpm, the growth temperature is 1030~1050℃, the H2:NH3 ratio is 9:1, the NH3 concentration is 40~50 L / min, N2 is set to 0, and the growth time is 30 seconds~5 minutes. The second GaN layer is a longitudinal growth layer. In this stage, the longitudinal growth rate is greater than the lateral growth rate, and the GaN layer height is approximately equal to the PSS height. The pressure and speed are the same as the first stage, the growth temperature is 1070~1090℃, the H2:NH3 ratio is 6:1, and the NH3 concentration is 45~55 L / min. The growth rate was set to L / min, N2 was 0, and the growth time was 8-15 minutes. The third GaN layer was the gap-filling layer between the GaN layer and PSS. The pressure and rotation speed in this section were the same as in the first section. The growth temperature was 1110-1130℃, N2 was 0, H2:NH3 = 5:1, and NH3 was between 60-70 L / min. The growth time was 5-8 minutes. The TMGa ratio of the three sections was 1:2:2.5, with the first section containing 5.52×10 L / min TMGa. -3 ~ 7.73×10 -3 mol / min; Step 5: On the GaN layer grown by the three-step growth method, an n-type GaN layer (500), a V-shaped pit forming layer (600), an MQW light-emitting layer (700), a low-temperature PGaN layer (800), an electron blocking layer (900), and a high-temperature PGaN layer (1000) are grown sequentially from bottom to top.

7. The epitaxial structure growth method for reducing defect density in blue-green Micro LEDs according to claim 6, characterized in that: The pulsed growth method in step three employs the following four-step process: Step 1: TMA1 (aluminum source) pulse injection, introducing only TMA1 and carrier gas N2, but not NH3. The TMA1 injection rate is 31.5~47 μmol / min, where it undergoes pyrolysis and adsorption on the high-temperature substrate surface, forming an aluminum atom layer or aluminum-containing intermediates, preparing for subsequent reactions. Step 2: Purge, shutting off TMA1 and introducing only carrier gas N2. This step aims to remove unadsorbed TMA1 and byproducts from the reaction chamber, preventing pre-reaction with the nitrogen source in the gas phase and ensuring growth primarily occurs through surface reactions. Step 3: NH3 (nitrogen source) pulse injection, introducing NH3 and carrier gas N2, reacting with the aluminum species already adsorbed on the substrate surface to generate an AlN monolayer. Step 4: Purge, shutting off NH3 again and introducing carrier gas N2 for purging to remove excess NH3 and reaction byproducts. These four steps constitute one cycle, with each step lasting 5, 3, 5, and 3 seconds respectively. The entire cycle is repeated 40-60 times.

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