GaN-based LED epitaxial structure and preparation method thereof
By introducing GaN nanopillars into the epitaxial structure of GaN-based LEDs, stress and dislocations are relieved, crystal quality is improved, structural damage caused by water vapor erosion is solved, and higher resistance to hydrolysis and reliability are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-31
- Publication Date
- 2026-07-03
AI Technical Summary
GaN-based LED devices are susceptible to moisture corrosion in humid outdoor environments, leading to structural damage and reduced reliability. Existing packaging protection relies on packaging integrity, and if the packaging fails, moisture can directly contact the epitaxial layer, causing irreversible damage.
Introducing GaN nanopillars into GaN-based LED epitaxial structures can alleviate stress, reduce dislocation density, improve crystal quality, enhance hydrolysis resistance, and prevent hydrolysis reactions.
It improves the hydrolysis resistance of GaN-based LED epitaxial structures, reduces packaging dependence, extends device life, and enhances reliability and stability, especially performing excellently in humid environments.
Smart Images
Figure CN122340981A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of LED device technology, and in particular to a GaN-based LED epitaxial structure and its fabrication method. Background Technology
[0002] Gallium nitride (GaN)-based light-emitting diodes (LEDs) have become core components in the semiconductor lighting field due to their outstanding advantages such as high luminous efficiency, long lifespan, and environmental friendliness. However, in humid outdoor environments, GaN-based LEDs face the severe challenge of moisture erosion. Moisture penetration severely damages the structural integrity and electrical performance of the devices, significantly reducing their reliability and lifespan, thus becoming a key bottleneck restricting the large-scale application of GaN-based LEDs in outdoor scenarios.
[0003] In existing technologies, improving the moisture resistance of GaN-based LED devices is mainly achieved through improved packaging processes, such as using high-airtightness packaging materials and optimizing the packaging structure, to reduce the ingress of moisture into the device and its contact with the chip body. However, this type of packaging-level protection is passive, and its effectiveness depends entirely on the integrity of the packaging. Once the packaging is damaged or ages, moisture will directly contact the epitaxial layer of the LED chip. After moisture contacts the LED epitaxial layer, the N-GaN and U-GaN layers not protected by passivation layers, as well as other transition layers that may exist between the U-GaN and N-GaN layers, are prone to hydrolysis, causing expansion and cracking of the epitaxial layer, resulting in irreversible damage to the LED device and affecting its reliability. Therefore, optimizing the structure of the LED epitaxial layer and improving its resistance to hydrolysis is of great significance. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to provide a GaN-based LED epitaxial structure and its preparation method, which can effectively reduce defect density, improve epitaxial layer quality, thereby slowing down the hydrolysis reaction of GaN and improving the hydrolysis resistance of GaN-based LED epitaxial structure.
[0005] To address the aforementioned technical problems, this invention provides a GaN-based LED epitaxial structure, comprising a substrate, and a mask layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer, and a p-GaN layer sequentially stacked on the substrate; The mask layer has a plurality of nanopores, which penetrate the mask layer along the thickness direction. GaN nanopillars are disposed within the nanopores, with one end of the GaN nanopillars connected to the substrate and the other end extending to the outside of the mask layer, so that a portion of the structure of the GaN nanopillars protrudes from the surface of the mask layer; The U-GaN layer covers the surface of the mask layer and the GaN nanopillars.
[0006] As an improvement to the above technical solution, the height of the portion of the GaN nanopillar protruding from the surface of the mask layer is 10nm~20nm; The total height of the GaN nanopillars is 30nm~70nm.
[0007] As an improvement to the above technical solution, the GaN nanopillars have a hexahedral columnar structure, and the side surfaces of the GaN nanopillars are {1 00} crystal plane.
[0008] As an improvement to the above technical solution, a plurality of the nanopores are distributed in an array on the mask layer; The diameter of the nanopore is 60 nm to 120 nm; The spacing between adjacent nanopores is 200 nm to 500 nm; The thickness of the mask layer is 20nm~50nm.
[0009] As an improvement to the above technical solution, the mask layer is a SiO2 layer or a SiNx layer; The thickness of the U-GaN layer is 1000nm~1500nm.
[0010] Accordingly, the present invention also provides a method for preparing a GaN-based LED epitaxial structure, which includes the following steps: (1) Provide a substrate; (2) Deposit a mask layer on the substrate; (3) Several nanopores are formed within the mask layer; (4) GaN nanopillars are formed within the nanopores; (5) Deposit a U-GaN layer on a mask layer with GaN nanopillars formed; (6) An N-GaN layer, a multiple quantum well layer, an electron blocking layer and a p-GaN layer are sequentially deposited on the U-GaN layer.
[0011] As an improvement to the above technical solution, in step (4), GaN nanopillars are formed in the nanopores using an MOCVD device, including the following steps: (4.1) Hydrogenation treatment is performed on the substrate with nanopores formed in the mask layer; (4.2) Nitride the mask layer with nanopores after step (4.1); (4.3) Introduce TMGa and NH3 to deposit a GaN nucleation layer in the nanopores; (4.4) Increase the flow rate of TMGa and decrease or turn off the flow rate of NH3 to form Ga droplets on the GaN nucleation layer and continue to grow until the diameter of the Ga droplets matches the diameter of the nanopores. (4.5) TMGa and NH3 were introduced, and V / Ⅲ < 15 was controlled to grow GaN nanopillars.
[0012] As an improvement to the above technical solution, in step (4.1), the temperature is controlled at 1000℃~1100℃, the pressure is controlled at 100Torr~200Torr, and only H2 is introduced to hydrogenate the substrate with nanopores formed in the mask layer. The flow rate of H2 in the hydrogenation process is 100L / min~200L / min. In step (4.2), the temperature is controlled at 500℃~650℃, the pressure is controlled at 200Torr~400Torr, only NH3 is introduced, and the flow rate of NH3 is controlled at >50L / min, to nitrid the mask layer with nanopores.
[0013] As an improvement to the above technical solution, in step (4.3), the temperature is controlled at 650℃~850℃, the pressure is controlled at 200Torr~400Torr, TMGa and NH3 are introduced, and the flow rate of TMGa is controlled at 100sccm~200sccm, and the flow rate of NH3 is >50L / min, so as to deposit and form a GaN nucleation layer in the nanopore. The thickness of the GaN nucleation layer is 5nm~10nm.
[0014] As an improvement to the above technical solution, in step (4.4), the temperature is increased to 750℃~850℃, the pressure is reduced to 100Torr~150Torr, the flow rate of TMGa is increased to >500sccm, and the flow rate of NH3 is reduced to <10L / min or NH3 is turned off, so that Ga droplets are formed on the GaN nucleation layer and continue to grow until the diameter of the Ga droplets grows to match the diameter of the nanopore. In step (4.5), the temperature is raised to 800℃~880℃, the pressure is controlled at 100Torr~150Torr, TMGa and NH3 are introduced, and V / Ⅲ is controlled to be <15 to grow GaN nanopillars.
[0015] Implementing this invention has the following beneficial effects: 1. This invention utilizes a mask layer with GaN nanopillars between a U-GaN layer and a substrate to grow an LED epitaxial layer. By leveraging the stress relief and lateral epitaxial function of the GaN nanopillars, the stress between the GaN layer and the substrate can be significantly reduced, dislocation density can be lowered, and crystal quality can be improved. Based on the reduction in dislocation density in the epitaxial layer, the number of carrier recombination centers in the U-GaN and N-GaN layers can be significantly reduced, the electrochemical reaction between H2O and GaN can be slowed down, and the stability of the GaN surface can be improved, making it less prone to H2O adsorption and thus less susceptible to hydrolysis. This effectively enhances the hydrolysis resistance of the LED epitaxial structure.
[0016] 2. GaN nanopillars exhibit a hexahedral columnar structure, with their lateral surfaces being {1} 00} crystal plane, {1 The 00} crystal plane is the equilibrium plane of GaN, with low surface energy, making it less prone to hydrolysis and further improving GaN's resistance to hydrolysis.
[0017] 3. This invention optimizes the epitaxial structure of GaN-based LEDs, enabling the epitaxial structure itself to possess excellent hydrolysis resistance, thus eliminating complete dependence on packaging processes. Even in the event of packaging failure, moisture is unlikely to hydrolyze the unpassivated N-GaN and U-GaN layers, preventing the epitaxial layers from expanding and cracking, ensuring normal chip illumination, and extending device lifespan. This active hydrolysis protection compensates for the shortcomings of traditional passive packaging, reduces the risk of LED device scrapping due to packaging failure, and improves the reliability and stability of LED devices under humid and harsh conditions. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of a GaN-based LED epitaxial structure according to an embodiment of the present invention; Figure 2 yes Figure 1 A partial enlarged view of the GaN-based LED epitaxial structure of the embodiment shown; Figure 3 yes Figure 1 A schematic diagram of step (3) in the method for preparing the GaN-based LED epitaxial structure of the embodiment shown; Figure 4 yes Figure 1 A schematic diagram of step (4.5) in the fabrication method of the GaN-based LED epitaxial structure of the embodiment shown; Figure 5 yes Figure 1 A schematic diagram of step (5) in the method for fabricating the GaN-based LED epitaxial structure of the embodiment shown; Among them: substrate 1, mask layer 2, U-GaN layer 3, N-GaN layer 4, multiple quantum well layer 5, electron blocking layer 6, p-GaN layer 7, GaN nanopillar 8, and nanopore 21. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.
[0020] Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Raw materials whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0021] See Figure 1 and Figure 2 As shown, an embodiment of a GaN-based LED epitaxial structure is disclosed, including a substrate 1, and a mask layer 2, a U-GaN layer 3, an N-GaN layer 4, a multiple quantum well layer 5, an electron blocking layer 6 and a p-GaN layer 7 sequentially stacked on the substrate 1; A number of nanopores 21 are formed in the mask layer 2, and the nanopores 21 penetrate the mask layer 2 along the thickness direction of the mask layer 2; A GaN nanopillar 8 is disposed inside the nanopore 21. One end of the GaN nanopillar 8 is connected to the substrate 1, and the other end extends to the outside of the mask layer 2, so that part of the structure of the GaN nanopillar 8 protrudes from the surface of the mask layer 2. U-GaN layer 3 covers the surface of mask layer 2 and GaN nanopillars 8.
[0022] It should be noted that in traditional GaN-based LED epitaxial structures, the significant differences in lattice constants and thermal expansion coefficients between the GaN layer and the substrate easily lead to stress accumulation, resulting in a high density of dislocation defects in the epitaxial layer. On the one hand, these defects readily become carrier recombination centers, accelerating electrochemical reactions, particularly the electrochemical reaction between H2O and GaN. On the other hand, these defects also readily adsorb impurities, reducing the stability of the GaN surface. The poor surface stability of GaN makes it even more prone to H2O adsorption, further exacerbating hydrolysis. Therefore, an increase in defects in the epitaxial layer intensifies the hydrolysis reaction. In a humid environment, the gallium hydroxide and other products generated by the hydrolysis reaction between GaN and water vapor disrupt the lattice structure of the GaN crystal, causing the epitaxial layer to expand and crack. This leads to degradation of the LED device's electrical performance, a decrease in luminous efficiency, and ultimately device failure. In particular, the N-GaN and U-GaN layers, which are not protected by a passivation layer, are more susceptible to hydrolysis, causing expansion and cracking of the epitaxial layer, thus affecting the reliability of the LED device.
[0023] This invention utilizes a mask layer 2 with GaN nanopillars 8 between a U-GaN layer 3 and a substrate 1 to grow an LED epitaxial layer. By leveraging the stress relief and lateral epitaxial function of the GaN nanopillars 8, the stress between the GaN layer and the substrate 1 can be significantly reduced, dislocation density can be lowered, and crystal quality can be improved. Based on the reduced dislocation density in the epitaxial layer, the number of carrier recombination centers in the U-GaN layer 3 and N-GaN layer 4 can be significantly reduced, the electrochemical reaction between H2O and GaN can be slowed down, and the stability of the GaN surface can be improved, making it less prone to H2O adsorption and thus less susceptible to hydrolysis. This effectively enhances the hydrolysis resistance of the LED epitaxial structure.
[0024] Further explanation reveals that GaN nanopillars 8 possess stress-relieving capabilities. Utilizing the structural characteristics of GaN nanopillars 8, the lateral stress (stress parallel to the substrate surface) generated during GaN film growth can be completely relaxed. This significantly reduces stress and strain from the substrate or underlying layer during GaN film growth, thereby improving crystal quality, reducing defect density in the epitaxial layer, and ultimately enhancing GaN's resistance to hydrolysis. The principle behind the stress-relieving function of GaN nanopillars 8 is as follows: Firstly, because GaN nanopillars 8 are nanoscale columnar structures, they introduce additional lateral free surfaces. Compared to traditional planar epitaxial structures, the lateral stress that was originally rigidly constrained in the planar structure can be effectively released through lateral deformation via these lateral free surfaces, reducing stress accumulation in the epitaxial layer. Secondly, the columnar structure of GaN nanopillars 8 can intercept dislocations generated during growth, causing them to terminate at the sidewalls of the GaN nanopillars 8, preventing dislocations from penetrating the entire epitaxial layer, thereby effectively reducing the dislocation density of the epitaxial layer and further improving crystal quality. Thirdly, slight shear deformation occurs near the sidewalls of GaN nanopillars 8, which can further help release the residual stress generated during the epitaxial layer growth process, allowing the stress that is difficult to release in traditional planar structures to decay rapidly at the nanoscale, thereby further reducing the adverse effects of stress on the crystal quality of GaN thin films.
[0025] To further illustrate, by controlling the partial structure of GaN nanopillars 8 to protrude from the surface of mask layer 2, it is beneficial to release and alleviate lateral stress.
[0026] This embodiment optimizes the epitaxial structure of GaN-based LEDs, enabling the optimized epitaxial structure to possess superior hydrolysis resistance, thereby enhancing the hydrolysis resistance of the LED device rather than relying entirely on the packaging process. Therefore, even if packaging failure occurs during LED device use, the optimized epitaxial layer's stronger hydrolysis resistance prevents moisture from entering the device and reacting with the unpassivated N-GaN, U-GaN layers, and related transition layers. This effectively avoids irreversible damage such as expansion and cracking of the epitaxial layer, ensuring the LED chip's normal light-emitting function remains unaffected and significantly extending the LED device's lifespan. Furthermore, this active hydrolysis protection achieved through optimized epitaxial layer structure overcomes the limitations of traditional passive packaging protection, reducing the risk of device failure due to packaging failure and improving the reliability and stability of GaN-based LED devices in complex application scenarios such as humid and harsh conditions.
[0027] In one embodiment, the height (h1) of the portion of the GaN nanopillar 8 protruding from the surface of the mask layer 2 is 10 nm to 20 nm; specifically, h1 is exemplary to be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm, but is not limited thereto.
[0028] It is worth noting that by controlling the height (h1) of the portion of the GaN nanopillar 8 protruding from the surface of the mask layer 2 to be 10nm~20nm, it is beneficial to further release and alleviate lateral stress, thereby further reducing the defect density of the epitaxial layer and further improving the hydrolysis resistance of the GaN-based LED epitaxial structure. If the height of the portion of the GaN nanopillar 8 protruding from the surface of the mask layer 2 is too low, the effect of alleviating the lateral stress of the epitaxial layer will be small, which will lead to a decrease in the hydrolysis resistance of the LED epitaxial structure; if the height of the protruding portion is too high, it will not only increase the growth difficulty of the GaN nanopillar 8, but also be detrimental to the subsequent epitaxial growth of the U-GaN layer.
[0029] In one embodiment, the total height (h2) of the GaN nanopillars 8 is 30 nm to 70 nm. Controlling the total height (h2) of the GaN nanopillars 8 to 30 nm to 70 nm is beneficial for further improving the hydrolysis resistance of the GaN-based LED epitaxial structure. If the total height (h2) of the GaN nanopillars 8 exceeds the specified range, it is not conducive to relieving the stress of the epitaxial layer and may even exacerbate the deterioration of the underlying epitaxial crystal quality, promoting hydrolysis reactions.
[0030] In one embodiment, the GaN nanopillars 8 have a hexahedral columnar structure, and the sides of the GaN nanopillars 8 are {1} 00)} crystal plane.
[0031] Specifically, gallium nitride typically exists in a hexagonal wurtzite structure, with its crystal planes mainly including the c-plane, m-plane, and a-plane. The c-plane is a polar plane, typically represented by the (0001) crystal plane; the m-plane and a-plane are both non-polar planes, with common m-planes including (1... 00) crystal plane, (10 0) crystal plane and (01) 0) Crystal plane; common a-planes include (1120) planes, etc. Because the (0001) crystal plane is a polar plane with a high density of surface dangling bonds and strong chemical activity, the (0001) crystal plane of gallium nitride materials is more prone to hydrolysis, leading to lattice destruction and degradation of the electrical performance of LED devices. In this embodiment, the GaN nanopillars have a hexahedral columnar structure, with their sides being {1 00} crystal plane (i.e., m plane), {1 The 00} crystal plane is the equilibrium plane of GaN, with low surface energy, making it less prone to hydrolysis and further improving GaN's resistance to hydrolysis.
[0032] In one embodiment, a plurality of nanopores 21 are distributed in an array on the mask layer 2; The diameter (d) of nanopore 21 is 60 nm to 120 nm; The spacing (s) between adjacent nanopores 21 is 200 nm to 500 nm; The thickness of mask layer 2 is 20nm~50nm.
[0033] By controlling the diameter of the nanopores 21 within the range of 60 nm to 120 nm, it is beneficial to rapidly grow GaN nanopillars 8. In this embodiment, the width of the prepared GaN nanopillars 8 matches the diameter of the nanopores 21, or is slightly smaller than the diameter of the nanopores 21. Furthermore, by controlling the spacing (s) between adjacent nanopores 21 to 200 nm to 500 nm, and controlling the thickness of the mask layer 2 to 20 nm to 50 nm, the merging speed of the U-GaN layer can be improved; this parameter adjustment method can alleviate lateral stress while improving the density of the GaN epitaxial layer, which is beneficial to improving the hydrolysis resistance of the GaN epitaxial layer.
[0034] Specifically, the diameter (d) of the nanopore 21 is exemplary to be 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm or 120nm, but is not limited thereto; the spacing (s) between adjacent nanopores 21 is exemplary to be 200nm, 250nm, 300nm, 350nm, 400nm, 45nm or 500nm, but is not limited thereto; the thickness of the mask layer 2 is exemplary to be 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, but is not limited thereto.
[0035] In one embodiment, the mask layer 2 is a SiO2 layer or a SiNx layer; The thickness of the U-GaN layer 3 is 1000nm to 1500nm. Specifically, the thickness of the U-GaN layer 3 is exemplary to be 1000nm, 1100nm, 1200nm, 1300nm, 1400nm or 1500nm, but is not limited thereto.
[0036] Accordingly, a method for fabricating a GaN-based LED epitaxial structure is also provided, comprising the following steps: (1) Provide a substrate 1; specifically, the substrate may be one of a sapphire substrate, a Si substrate or a silicon carbide substrate; (2) Deposit mask layer 2 on substrate 1; (3) Several nanopores 21 are formed in the mask layer 2; (4) GaN nanopillars 8 are formed inside the nanopore 21; (5) Deposit a U-GaN layer 3 on the mask layer 2 on which GaN nanopillars 8 are formed; (6) An N-GaN layer 4, a multi-quantum well layer 5, an electron blocking layer 6 and a p-GaN layer 7 are sequentially deposited on the U-GaN layer 3.
[0037] It is worth noting that the method of this embodiment can form GaN nanopillars 8 in the mask layer 2. By utilizing the stress relief and lateral epitaxial function of the GaN nanopillar structure, the stress between the GaN layer and the substrate 1 can be reduced, the dislocation density can be reduced and the crystal quality can be improved, making the GaN material less prone to hydrolysis reaction, thereby improving the hydrolysis resistance of the GaN-based LED epitaxial structure.
[0038] Specifically, lateral epitaxy refers to epitaxial growth on a patterned substrate with a mask, where the lateral growth rate of the epitaxial material is greater than the longitudinal growth rate. This causes the epitaxial layer, initially selectively grown within a window region, to extend laterally outwards, eventually splicing together to form a continuous and complete epitaxial layer. This approach combines a patterned mask layer with GaN nanopillars to create a novel patterned epitaxial template, enabling lateral epitaxial growth.
[0039] In one embodiment, in step (2), silicon dioxide (SiO2) or silicon nitride (SiN) can be deposited on the surface of substrate 1 using plasma-enhanced chemical vapor deposition (PECVD). x The thin film serves as mask layer 2. Using PECVD technology, a mask film with uniform thickness and high density can be prepared, providing a basis for subsequent etching of nanopores. Preferably, the thickness of mask layer 2 is 20 nm to 50 nm.
[0040] In one embodiment, step (3) involves patterning the mask layer 2 using photolithography and etching processes to form a plurality of nanopores 21 penetrating the mask layer along the thickness direction. See [link to relevant documentation]. Figure 3 As shown.
[0041] In one embodiment, in step (4), GaN nanopillars 8 are formed within the nanopores 21 using an MOCVD device, including the following steps: (4.1) Hydrogenation treatment of the substrate 1 with nanopores 21 formed in the mask layer 2 can remove oxygen and other adsorbed impurities from the surface. (4.2) Nitriding the mask layer 2 with nanopores 21 after step (4.1) can effectively reduce the interface energy and make GaN easier to nucleate; (4.3) TMGa and NH3 are introduced to deposit a GaN nucleation layer in the nanopore 21; (4.4) Increase the flow rate of TMGa and decrease or turn off the flow rate of NH3 to form Ga droplets on the GaN nucleation layer and continue to grow until the diameter of the Ga droplets matches the diameter of the nanopore 21. (4.5) TMGa and NH3 were introduced, and V / Ⅲ < 15 was controlled to grow GaN nanopillars 8.
[0042] Specifically, V / III refers to the ratio of the molar flux of the group V element source (NH3) to the molar flux of the group III element source (TMGa) during the epitaxial growth process. By controlling the V / III molar ratio to be less than 15, GaN nanopillars can be grown.
[0043] Specifically, the prepared substrate template with arrayed nanopores 21 is placed in an MOCVD device for epitaxial growth.
[0044] In one embodiment, in step (4.1), the temperature is controlled at 1000℃~1100℃, the pressure is 100Torr~200Torr, and H2 is introduced to hydrogenate the substrate 1 with nanopores 21 formed in the mask layer 2. The flow rate of H2 in the hydrogenation process is 100L / min~200L / min. By performing high-temperature hydrogenation on the substrate template with arrayed nanopores 21 under the condition of only introducing H2, oxygen and other adsorbed impurities on the surface can be removed.
[0045] In one embodiment, in step (4.2), the temperature is controlled at 500℃~650℃, the pressure at 200Torr~400Torr, and only NH3 is introduced, with the NH3 flow rate controlled at >50L / min, to nitrid the mask layer 2 on which the nanopores 21 are formed. Under these temperature conditions, nitriding with a high flow rate of NH3 can form an N-containing transition layer (such as an AlN transition layer or a SiN transition layer) in the window region (i.e., the open area of the nanopores), which can reduce the interface energy. Moreover, compared with GaN grown directly on a sapphire substrate or SiO2, AlN or SiN is a homoepitaxial growth for GaN epitaxy, which is more conducive to the epitaxial nucleation and growth of GaN. Specifically, the thickness of the N-containing transition layer formed in the window region is 0.5nm~1nm.
[0046] Optionally, in step (4.2), the flow rate of NH3 is 55 L / min to 100 L / min.
[0047] In one embodiment, in step (4.3), the temperature is controlled at 650℃~850℃, the pressure is controlled at 200 Torr~400 Torr, TMGa and NH3 are introduced, and the flow rate of TMGa is controlled at 100 sccm~200 sccm, and the flow rate of NH3 is >50 L / min. Taking advantage of the characteristic that GaN is difficult to nucleate on SiO2, a GaN nucleation layer is deposited in the nanopore 21, which can provide nucleation sites for subsequent GaN droplets. Optionally, in step (4.3), the flow rate of NH3 is maintained at 55 L / min~100 L / min.
[0048] In one embodiment, the thickness of the GaN nucleation layer is 5 nm to 10 nm. Specifically, the thickness of the GaN nucleation layer is exemplary to be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, but is not limited thereto.
[0049] In one embodiment, in step (4.4), the temperature is increased to 750°C to 850°C, the pressure is reduced to 100 Torr to 150 Torr, the flow rate of TMGa is increased to >500 sccm, and the flow rate of NH3 is reduced to <10 L / min or NH3 is turned off, so that Ga droplets are formed on the GaN nucleation layer and continue to grow until the diameter of the Ga droplets matches the diameter of the nanopore 21; in step (4.4), excess TMGa can form Ga droplets at the nucleation sites in the window region until the diameter of the Ga droplets matches the diameter of the nanopore 21 to reach 60 nm to 120 nm.
[0050] See Figure 4 As shown, in one embodiment, in step (4.5), the temperature is raised to 800℃~880℃, the pressure is controlled to 100Torr~150Torr, TMGa and NH3 are introduced, and V / Ⅲ is controlled to be <15. Under these conditions, GaN will gradually precipitate at the bottom and grow along the axial direction. Lateral growth will be blocked by the SiO2 mask, thereby growing GaN nanopillars 8.
[0051] In one embodiment, in step (4.5), NH3 can be continuously introduced or intermittently introduced, with an intermittent time of 5 to 10 seconds.
[0052] See Figure 5 As shown, in one embodiment, the method of depositing a U-GaN layer 3 on a mask layer 2 on which GaN nanopillars 8 are formed in step (5) includes the following steps: Based on the underlying structure of GaN nanopillars 8, undoped GaN layers (i.e., U-GaN layers) are epitaxially grown at temperatures of 1100℃~1150℃ and pressures of 150Torr~200Torr, with a thickness of 1000nm~1500nm. By utilizing the complete relaxation of lateral stress in the underlying structure of the GaN nanopillars, the stress and strain from the substrate or underlying layer during the growth of GaN films (such as U-GaN layer 3, N-GaN layer 4, etc.) can be significantly reduced, thereby improving crystal quality, reducing the defect density of the epitaxial layer, and thus enhancing the hydrolysis resistance of GaN.
[0053] It should be noted that in step (6), N-GaN layer 4, multi-quantum well layer 5, electron blocking layer 6 and p-GaN layer 7 are deposited sequentially on U-GaN layer 3. These can be grown using conventional conditions and parameters in the art, and there are no limitations on this.
[0054] The technical solution of the present invention will be further illustrated below through embodiments and comparative examples.
[0055] Example 1 This embodiment discloses a GaN-based LED epitaxial structure, including a substrate, and a mask layer (SiO2 layer), a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer, and a p-GaN layer sequentially stacked on the substrate; the mask layer has a plurality of nanopores that penetrate the mask layer along its thickness direction; GaN nanopillars are disposed within the nanopores, with one end of the GaN nanopillars connected to the substrate and the other end extending to the outside of the mask layer, so that part of the structure of the GaN nanopillars protrudes from the surface of the mask layer; the U-GaN layer covers the surfaces of the mask layer and the GaN nanopillars; Among them, several nanopores are distributed in an array on the mask layer. The diameter of the nanopores is 100nm, the spacing between adjacent nanopores is 300nm, and the thickness of the mask layer is 30nm. The total height of the GaN nanopillars is 45nm, and the height of the part of the GaN nanopillars protruding from the surface of the mask layer is 15nm. The thickness of the U-GaN layer is 1200nm.
[0056] The method for fabricating the GaN-based LED epitaxial structure in this embodiment includes the following steps: (1) Provide a substrate; (2) Deposit a mask layer on the substrate; (3) Several nanopores are formed within the mask layer; (4) GaN nanopillars are formed within the nanopores; (5) Deposit a U-GaN layer on a mask layer with GaN nanopillars formed; (6) An N-GaN layer, a multi-quantum well layer, an electron blocking layer and a p-GaN layer are sequentially deposited on the U-GaN layer.
[0057] In step (4), GaN nanopillars are formed in the nanopores using an MOCVD device, including the following steps: (4.1) The temperature is controlled at 1100℃, the pressure is 200 Torr, and only H2 is introduced at a flow rate of 150 L / min to hydrogenate the substrate with nanopores formed in the mask layer. (4.2) The mask layer with nanopores after step (4.1) is nitrided by controlling the temperature at 550℃, the pressure at 300 Torr, and only NH3 is introduced, and the flow rate of NH3 is controlled at 70 L / min. (4.3) The temperature was controlled at 750℃ and the pressure was controlled at 300 Torr. TMGa and NH3 were introduced, and the flow rate of TMGa was controlled at 180 sccm and the flow rate of NH3 was kept at 70 L / min. A GaN nucleation layer with a thickness of 6 nm was deposited in the nanopore. (4.4) Increase the temperature to 800℃, reduce the pressure to 120 Torr, increase the flow rate of TMGa to 800 sccm, and turn off NH3 to form Ga droplets on the GaN nucleation layer. Continue to grow until the diameter of the Ga droplets reaches 100 nm. (4.5) While maintaining the flow of TMGa, resume the flow of NH3 and control V / Ⅲ=10. Increase the temperature to 850℃ and control the pressure to 120 Torr to start forming GaN nanopillars. Continue to grow until the height of the part of the GaN nanopillar protruding from the surface of the mask layer reaches 15nm, and GaN nanopillars are obtained.
[0058] In step (5), based on the GaN nanopillar bottom structure, a U-GaN layer is further epitaxially grown at a temperature of 1110℃ and a pressure of 180 Torr to obtain a U-GaN layer with a thickness of 1200 nm.
[0059] Example 2 This embodiment discloses a GaN-based LED epitaxial structure. The GaN-based LED epitaxial structure of Embodiment 2 is basically the same as that of Embodiment 1, except that: The diameter of the nanopores is 60 nm, the spacing between adjacent nanopores is 200 nm, the total height of the GaN nanopillars is 40 nm, and the height of the GaN nanopillars protruding from the mask layer surface is 10 nm.
[0060] Comparative Example 1 This comparative example provides an LED epitaxial structure, including a substrate, and an AlN layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer, and a p-GaN layer sequentially stacked on the substrate. The fabrication method of this comparative example LED epitaxial structure includes the following steps: (1) First, an AlN layer is grown on the substrate using PVD. The thickness of the AlN layer is 20 nm. Then, the substrate with the AlN layer is placed in MOCVD for epitaxial growth. First, an undoped U-GaN layer is grown at a growth temperature of 1110℃, a pressure of 180 Torr, and a thickness of 1200 nm. (2) An N-GaN layer, a multi-quantum well layer, an electron blocking layer and a p-GaN layer are grown sequentially on the U-GaN layer to obtain an LED epitaxial structure.
[0061] Comparative Example 2 This comparative example discloses a GaN-based LED epitaxial structure. The GaN-based LED epitaxial structure of Comparative Example 2 is basically the same as that of Example 1, except that: The diameter of the nanopores is 150 nm, the spacing between adjacent nanopores is 700 nm, the total height of the GaN nanopillars is 32 nm, and the height of the GaN nanopillars protruding from the mask layer surface is 2 nm.
[0062] Performance testing The LED epitaxial structures obtained in Examples 1, 2, 1, and 2 were fabricated into LED chips using the same chip process conditions. They were aged for 528 hours under "double 85" conditions (temperature 85°C and humidity 85%) and at a current of 30mA. During the test, the reverse leakage current of the samples was counted every 24 hours (tested at -10V). The reverse leakage current (IR) reflects the hydrolysis resistance of the samples. The test results are shown in Table 1 below.
[0063] Table 1 Reverse leakage current test results
[0064] As can be observed from Table 1, compared with the LED epitaxial structures of Comparative Examples 1 and 2, the GaN-based LED epitaxial structures prepared in Examples 1 and 2 have better hydrolysis resistance, and the GaN-based LED epitaxial structure of Example 1 has superior hydrolysis resistance. The LED chip prepared using the GaN-based LED epitaxial structure of Example 1 only increased its reverse leakage current (IR) to 0.001 μA after 360 h of aging, while the LED chip prepared using the conventional epitaxial structure in Comparative Example 1 increased its reverse leakage current (IR) to 0.001 μA after 168 h; moreover, when the aging time reached 528 h, the reverse leakage current (IR) of the LED chip of Example 1 was still 0.001 μA, while the reverse leakage current (IR) of the LED chip of Comparative Example 1 at this time was 0.004 μA, which is 4 times that of Example 1. It is evident that the reverse leakage current (IR) of Example 1 changes over a longer period of time under high temperature and high humidity conditions of 85°C and 85%, and the change in reverse leakage current (IR) is smaller as the aging time increases. Therefore, the hydrolysis resistance of the LED chip prepared by the epitaxial structure of Example 1 is significantly better than that of the LED chip prepared by the conventional epitaxial structure in Comparative Example 1.
[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A GaN-based LED epitaxial structure, characterized in that, It includes a substrate, and a mask layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer and a p-GaN layer sequentially stacked on the substrate; The mask layer has a plurality of nanopores, which penetrate the mask layer along the thickness direction. GaN nanopillars are disposed within the nanopores, with one end of the GaN nanopillars connected to the substrate and the other end extending to the outside of the mask layer, so that a portion of the structure of the GaN nanopillars protrudes from the surface of the mask layer; The U-GaN layer covers the surface of the mask layer and the GaN nanopillars.
2. The GaN-based LED epitaxial structure according to claim 1, characterized in that, The height of the portion of the GaN nanopillars protruding from the surface of the mask layer is 10nm~20nm; The total height of the GaN nanopillars is 30nm~70nm.
3. The GaN-based LED epitaxial structure according to claim 1, characterized in that, The GaN nanopillars have a hexahedral columnar structure, and the sides of the GaN nanopillars are {1} 00} crystal plane.
4. The GaN-based LED epitaxial structure according to claim 3, characterized in that, Several of the nanopores are distributed in an array on the mask layer; The diameter of the nanopore is 60 nm to 120 nm; The spacing between adjacent nanopores is 200 nm to 500 nm; The thickness of the mask layer is 20nm~50nm.
5. The GaN-based LED epitaxial structure according to claim 1, characterized in that, The mask layer is a SiO2 layer or a SiNx layer; The thickness of the U-GaN layer is 1000nm~1500nm.
6. A method for fabricating a GaN-based LED epitaxial structure, characterized in that, The method for preparing the GaN-based LED epitaxial structure according to any one of claims 1-5 comprises the following steps: (1) Provide a substrate; (2) Deposit a mask layer on the substrate; (3) Several nanopores are formed within the mask layer; (4) GaN nanopillars are formed within the nanopores; (5) Deposit a U-GaN layer on a mask layer with GaN nanopillars formed; (6) An N-GaN layer, a multiple quantum well layer, an electron blocking layer and a p-GaN layer are sequentially deposited on the U-GaN layer.
7. The method for preparing a GaN-based LED epitaxial structure according to claim 6, characterized in that, In step (4), GaN nanopillars are formed within the nanopores using an MOCVD device, including the following steps: (4.1) Hydrogenation treatment is performed on the substrate with nanopores formed in the mask layer; (4.2) Nitride the mask layer with nanopores after step (4.1); (4.3) Introduce TMGa and NH3 to deposit a GaN nucleation layer in the nanopores; (4.4) Increase the flow rate of TMGa and decrease or turn off the flow rate of NH3 to form Ga droplets on the GaN nucleation layer and continue to grow until the diameter of the Ga droplets matches the diameter of the nanopores. (4.5) TMGa and NH3 were introduced, and V / Ⅲ < 15 was controlled to grow GaN nanopillars.
8. The method for preparing a GaN-based LED epitaxial structure according to claim 7, characterized in that, In step (4.1), the temperature is controlled at 1000℃~1100℃, the pressure is controlled at 100Torr~200Torr, and only H2 is introduced to hydrogenate the substrate with nanopores formed in the mask layer. The flow rate of H2 in the hydrogenation process is 100L / min~200L / min. In step (4.2), the temperature is controlled at 500℃~650℃, the pressure is controlled at 200Torr~400Torr, only NH3 is introduced, and the flow rate of NH3 is controlled at >50L / min, to nitrid the mask layer with nanopores.
9. The method for preparing a GaN-based LED epitaxial structure according to claim 7, characterized in that, In step (4.3), the temperature is controlled at 650℃~850℃, the pressure is controlled at 200Torr~400Torr, TMGa and NH3 are introduced, and the flow rate of TMGa is controlled at 100sccm~200sccm, and the flow rate of NH3 is >50L / min, so as to deposit and form a GaN nucleation layer in the nanopore. The thickness of the GaN nucleation layer is 5nm~10nm.
10. The method for preparing a GaN-based LED epitaxial structure according to claim 7, characterized in that, In step (4.4), the temperature is increased to 750℃~850℃, the pressure is reduced to 100Torr~150Torr, the flow rate of TMGa is increased to >500sccm, and the flow rate of NH3 is reduced to <10L / min or NH3 is turned off, Ga droplets are formed on the GaN nucleation layer, and growth continues until the diameter of the Ga droplets grows to match the diameter of the nanopores; In step (4.5), the temperature is raised to 800℃~880℃, the pressure is controlled at 100Torr~150Torr, TMGa and NH3 are introduced, and V / Ⅲ is controlled to be <15 to grow GaN nanopillars.