A low operating current density blue Micro-LED epitaxial structure and its fabrication method

Abstract

This invention discloses a low-current-density blue Micro-LED epitaxial structure and its fabrication method, relating to the field of semiconductor device technology. The multi-quantum-well emitting layer of the epitaxial structure comprises, sequentially stacked along the epitaxial direction, a violet multi-quantum-well layer, a light blue multi-quantum-well layer, a blue multi-quantum-well layer, and a violet-light-end quantum-well layer. Each of the violet, light blue, blue, and violet-light-end quantum-well layers includes, sequentially and periodically alternating N-polarity gradient InGaN layer before the well, an N-polarity InGaN quantum-well layer, an N-polarity gradient AlGaN layer after the well, and a Ga-polarity GaN quantum barrier layer. The N-polarity gradient InGaN layer before the well is an N-polarity InGaN material with an increasing In content along the epitaxial direction. This invention can significantly improve the luminous efficacy of Micro-LED chips at low operating current densities.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a low operating current density blue Micro-LED epitaxial structure and its fabrication method. Background Technology

[0002] With the rapid development of emerging wearable and portable technologies, micron-sized LED chips (Micro-LEDs) have garnered significant attention and research from scientific institutions and enterprises due to their promising applications in displays, visible light communication, and biomedicine. Furthermore, Micro-LED displays possess nanosecond (ns) level high-speed response performance, the stability of inorganic materials, and excellent properties such as high luminous efficiency, high reliability, high color purity, high contrast, and transparency—combinations of characteristics that are difficult to achieve with liquid crystal displays (LCDs) and organic LEDs (OLEDs).

[0003] While Micro-LEDs possess many superior characteristics, they also face challenges in manufacturing technology and material / device physics. For example, the issue of decreasing peak EQE and correspondingly increasing current density as chip size decreases has not yet been fully resolved, limiting the operating current density to 0.01~0.5 A / cm². 2 The efficiency of Micro-LEDs in this range remains significantly insufficient. In fact, even standard-sized chips used in general lighting and backlighting applications exhibit relatively low efficiency at this current density. This is because standard-sized chips typically operate at a current density of 20 A / cm² to balance efficiency and cost. 2 Up to 40A / cm 2 Between these two points, the corresponding epitaxial structure design and material growth aim to improve efficiency under high current density, with its peak EQE typically around 1 A / cm². 2 ~4A / cm 2 The study focuses on the current density range, neglecting to consider device efficiency at low current densities. The dominant factors in the light-emitting mechanism of LED devices differ at different current densities, and the corresponding epitaxial layer structure should also change. For example, in the Micro-LED operating range at 0.01 A / cm²... 2 ~0.5A / cm 2At low current densities, the carrier concentration in the quantum well is relatively low, resulting in a smaller Auger recombination rate and a corresponding reduction in the quantum well recombination volume. This reduces the number of quantum wells and defects, improving the EQE (equivalent quantum efficiency) of the device at low current densities. Simultaneously, at low current densities, electron leakage has not yet occurred or is very low. The electron blocking layer structure not only fails to block electrons but also blocks hole injection, reducing the device's quantum efficiency. Therefore, in-depth mechanistic research, design, and growth of epitaxial layer structures under low current density operating conditions for Micro-LEDs are essential key technologies for developing high-efficiency Micro-LED devices driven by low operating current densities.

[0004] Traditional visible light LED epitaxial structure designs are primarily based on applications requiring large chips, high current, and high power. However, Micro-LED display applications demand small size, low current, and low power, making traditional epitaxial structure designs insufficient for their requirements. Therefore, redesigning epitaxial structures suitable for small-size, low-current, and low-power Micro-LEDs, and improving their electro-optical conversion efficiency, is a significant challenge facing both academia and industry. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to propose a low operating current density blue Micro-LED epitaxial structure, which can improve the luminous efficacy of Micro-LED chips at low operating current densities.

[0006] Another objective of this invention is to provide a method for fabricating a low-current-density blue Micro-LED epitaxial structure, which can improve the luminous efficacy of Micro-LED chips at low operating current densities.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] A low operating current density blue Micro-LED epitaxial structure includes a substrate, and further includes a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum well light-emitting layer and a P-type semiconductor layer sequentially stacked on the substrate, and no electron blocking layer is disposed above the multi-quantum well light-emitting layer;

[0009] The multi-quantum-well light-emitting layer includes a violet multi-quantum-well layer, a light blue multi-quantum-well layer, a blue multi-quantum-well layer, and a violet final quantum-well layer, which are stacked sequentially along the epitaxial direction.

[0010] The violet multi-quantum well layer, the light blue multi-quantum well layer, the blue multi-quantum well layer, and the violet end-quantum well layer all include N-polar gradient InGaN layer before the well, N-polar InGaN quantum well layer, N-polar gradient AlGaN layer after the well, and Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction.

[0011] The In content of the blue light multi-quantum well layer is greater than that of the light blue light multi-quantum well layer, and the In content of both the violet light multi-quantum well layer and the violet light end-quantum well layer is less than that of the light blue light multi-quantum well layer.

[0012] The N-polar in-well gradient InGaN layer is an N-polar InGaN material with increasing In content along the epitaxial direction, and the N-polar in-well gradient AlGaN layer is an N-polar AlGaN material with decreasing Al content along the epitaxial direction.

[0013] As an improvement to the above technical solution, the Al component content of the N-polar well-after gradient AlGaN layer in the violet light quantum well layer is ≤ the Al component content of the N-polar well-after gradient AlGaN layer in the blue light multi-quantum well layer is ≤ the Al component content of the N-polar well-after gradient AlGaN layer in the light blue light multi-quantum well layer is ≤ the Al component content of the N-polar well-after gradient AlGaN layer in the violet light multi-quantum well layer.

[0014] As an improvement to the above technical solution, the In content of the N-polar gradient InGaN layer in the blue light multi-quantum well layer is ≥ the In content of the N-polar gradient InGaN layer in the light blue light multi-quantum well layer.

[0015] The In content of the N-polar gradient InGaN layer in both the violet multi-quantum well layer and the violet end-quantum well layer is less than or equal to the In content of the N-polar gradient InGaN layer in the light blue multi-quantum well layer.

[0016] As an improvement to the above technical solution, the In composition content of the N-polar InGaN quantum well layer in the purple light multi-quantum well layer is Y1;

[0017] The In component content of the N-polar InGaN quantum well layer in the light blue light multi-quantum well layer is Y2;

[0018] The In component content of the N-polar InGaN quantum well layer in the blue light multi-quantum well layer is Y3;

[0019] The In composition content of the N-polar InGaN quantum well layer in the purple light-emitting quantum well layer is Y4;

[0020] Where Y1 < Y2 < Y3, and Y4 < Y2.

[0021] As an improvement to the above technical solution, the N-polar in-well gradient InGaN layer, the N-polar InGaN quantum well layer and the N-polar in-well gradient AlGaN layer of the purple light multi-quantum well layer are respectively the first N-polar in-well gradient InGaN layer, the first N-polar InGaN quantum well layer and the first N-polar in-well gradient AlGaN layer.

[0022] Along the epitaxial direction, the In composition content of the first N-polar well-preceded gradient InGaN layer increases from Y11 to Y12, where 0≤Y11≤0.02 and 0.10≤Y12≤0.14.

[0023] The In composition content of the first N-polar InGaN quantum well layer is Y1, wherein 0.10≤Y1≤0.14;

[0024] Along the epitaxial direction, the Al composition content of the first N-polar well-derived graded AlGaN layer decreases from X11 to X12, where 0.08 < X11 ≤ 0.25 and 0 ≤ X12 ≤ 0.08.

[0025] As an improvement to the above technical solution, the N-polar gradient InGaN layer before the light blue light multi-quantum well layer, the N-polar InGaN quantum well layer and the N-polar gradient AlGaN layer after the light blue light multi-quantum well layer are respectively the second N-polar gradient InGaN layer before the N-polar well, the second N-polar InGaN quantum well layer and the second N-polar gradient AlGaN layer after the N-polar well.

[0026] Along the epitaxial direction, the In composition content of the second N-polar well-precessed gradient InGaN layer increases from Y21 to Y22, where 0≤Y21≤0.03 and 0.14≤Y22≤0.16.

[0027] The In composition content of the second N-polar InGaN quantum well layer is Y2, wherein 0.14≤Y2≤0.16;

[0028] Along the epitaxial direction, the Al composition content of the second N-polar well-followed gradient AlGaN layer decreases from X21 to X22, where 0.06 < X21 ≤ 0.21 and 0 ≤ X22 ≤ 0.06.

[0029] As an improvement to the above technical solution, the N-polar gradient InGaN layer before the blue light multi-quantum well layer, the N-polar InGaN quantum well layer and the N-polar gradient AlGaN layer after the blue light multi-quantum well layer are respectively the third N-polar gradient InGaN layer before the N-polar well, the third N-polar InGaN quantum well layer and the third N-polar gradient AlGaN layer after the N-polar well.

[0030] Along the epitaxial direction, the In composition content of the third N-polar well-preceded gradient InGaN layer increases from Y31 to Y32, where 0≤Y31≤0.05 and 0.16≤Y32≤0.19.

[0031] The In composition of the third N-polar InGaN quantum well layer is Y3, wherein 0.16≤Y3≤0.19;

[0032] Along the epitaxial direction, the Al composition content of the third N-polar well-followed gradient AlGaN layer decreases from X31 to X32, where 0.05 < X31 ≤ 0.18 and 0 ≤ X32 ≤ 0.05.

[0033] As an improvement to the above technical solution, the N-polarity gradient InGaN layer before the quantum well, the N-polarity InGaN quantum well layer and the N-polarity gradient AlGaN layer after the quantum well are respectively the fourth N-polarity gradient InGaN layer before the quantum well, the fourth N-polarity InGaN quantum well layer and the fourth N-polarity gradient AlGaN layer after the quantum well.

[0034] Along the epitaxial direction, the In composition content of the fourth N-polar well-precessed gradient InGaN layer increases from Y41 to Y42, where 0≤Y41≤0.02 and 0.10≤Y42≤0.14.

[0035] The In composition of the fourth N-polar InGaN quantum well layer is Y4, wherein 0.10≤Y4≤0.14;

[0036] Along the epitaxial direction, the Al composition content of the fourth N-polar well-followed gradient AlGaN layer decreases from X41 to X42, where 0.03 < X41 ≤ 0.15 and 0 ≤ X42 ≤ 0.03.

[0037] As an improvement to the above technical solution, Si element is doped in the first, second, third, and fourth N-polar well-pre-graded InGaN layers, with a Si doping concentration of 1.12 × 10⁻⁶. 17 / cm 3 ~6.75×10 17 / cm 3 The growth thickness was 0.1 nm to 0.8 nm.

[0038] The first, second, third, and fourth N-polar InGaN quantum well layers are all made of undoped N-polar InGaN material, and their growth thicknesses range from 2.1 nm to 4.8 nm.

[0039] No intentional doping is performed in the first, second, third, and fourth N-polar well-tailed AlGaN layers, and the growth thickness of each layer is 0.1 nm to 0.8 nm.

[0040] The Ga polar GaN quantum barrier layers in the violet light multi-quantum well layer, the light blue light multi-quantum well layer, the blue light multi-quantum well layer, and the violet light final quantum well layer are all Ga polar GaN materials doped with Si, with a growth thickness of 6nm~13nm and a Si doping concentration of 2.15×10⁻⁶. 17 / cm 3 ~8.79×10 17 / cm 3 .

[0041] As an improvement to the above technical solution, the growth temperature of the N-polar gradient InGaN layer in the violet multi-quantum well layer and the violet end quantum well layer is ≥ the growth temperature of the N-polar gradient InGaN layer in the light blue multi-quantum well layer and the growth temperature of the N-polar gradient InGaN layer in the blue multi-quantum well layer, respectively.

[0042] As an improvement to the above technical solution, the growth temperature of the first N-polar gradient InGaN layer before the well is 775℃~920℃, the growth temperature of the second N-polar gradient InGaN layer before the well is 760℃~920℃, the growth temperature of the third N-polar gradient InGaN layer before the well is 750℃~920℃, and the growth temperature of the fourth N-polar gradient InGaN layer before the well is 775℃~920℃.

[0043] As an improvement to the above technical solution, the growth temperature of the first N-polar InGaN quantum well layer is greater than that of the second N-polar InGaN quantum well layer and the third N-polar InGaN quantum well layer, and the growth temperature of the fourth N-polar InGaN quantum well layer is greater than that of the second N-polar InGaN quantum well layer.

[0044] Accordingly, the present invention also provides a method for fabricating a low-current-density blue Micro-LED epitaxial structure, comprising the following steps:

[0045] (1) Selecting a substrate;

[0046] (2) A buffer layer is grown on the substrate;

[0047] (3) Introduce a Si doping source to grow an N-type semiconductor layer on the buffer layer;

[0048] (4) A low-temperature stress relief layer is grown on the N-type semiconductor layer;

[0049] (5) A multi-quantum well light-emitting layer is grown on the low-temperature stress relief layer;

[0050] (6) A P-type semiconductor layer is grown on the multi-quantum-well light-emitting layer;

[0051] The multi-quantum-well emitting layer comprises a violet multi-quantum-well layer, a light blue multi-quantum-well layer, a blue multi-quantum-well layer, and a violet end-quantum-well layer stacked sequentially along the epitaxial direction; the In content of the blue multi-quantum-well layer is greater than that of the light blue multi-quantum-well layer, and the In content of both the violet multi-quantum-well layer and the violet end-quantum-well layer is less than that of the light blue multi-quantum-well layer;

[0052] The violet multi-quantum well layer, the light blue multi-quantum well layer, the blue multi-quantum well layer, and the violet end-quantum well layer all include N-polar gradient InGaN layer before the well, N-polar InGaN quantum well layer, N-polar gradient AlGaN layer after the well, and Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction.

[0053] The N-polar well-before gradient InGaN layer is an N-polar InGaN material with increasing In content along the epitaxial direction, and the N-polar well-before gradient AlGaN layer is an N-polar AlGaN material with decreasing Al content along the epitaxial direction.

[0054] After the N-polar InGaN quantum well layers in the light blue light multi-quantum well layer and the violet light final quantum well layer are periodically deposited and grown alternately, the surface of the epitaxial layer material needs to be annealed.

[0055] Implementing this invention has the following beneficial effects: This invention redesigns the epitaxial structure suitable for small-size, low-current, and low-power Micro-LEDs, which can significantly improve the quality of the multi-quantum-well light-emitting layer and improve the matching degree of electron-hole concentration in the light-emitting quantum well region, thereby increasing the radiative recombination efficiency of the light-emitting quantum well region and thus improving the luminous efficacy of the Micro-LED chip at low operating current density. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of an embodiment of the low operating current density blue Micro-LED epitaxial structure of the present invention;

[0057] Figure 2 This is a schematic diagram of an embodiment of the multi-quantum-well light-emitting layer in the low operating current density blue Micro-LED epitaxial structure of the present invention;

[0058] In the diagram: 100 - substrate, 200 - buffer layer, 300 - N-type semiconductor layer, 400 - low-temperature stress relief layer, 500 - multi-quantum-well light-emitting layer, 600 - P-type semiconductor layer, 510 - violet multi-quantum-well layer, 520 - light blue multi-quantum-well layer, 530 - blue multi-quantum-well layer, 540 - violet quantum-well layer, 511 - first N-polarity well-front gradient InGaN layer, 512 - first N-polarity InGaN quantum-well layer, 513 - first N-polarity well-back gradient AlGaN layer, 514 - first Ga-polarity GaN quantum barrier layer, 521 - second N-polarity well-front gradient InGaN layer. 522 - Second N-polar InGaN quantum well layer, 523 - Second N-polar AlGaN layer with gradient after the well, 524 - Second Ga-polar GaN quantum barrier layer, 531 - Third N-polar InGaN layer with gradient before the well, 532 - Third N-polar InGaN quantum well layer, 533 - Third N-polar AlGaN layer with gradient after the well, 534 - Third Ga-polar GaN quantum barrier layer, 541 - Fourth N-polar InGaN layer with gradient before the well, 542 - Fourth N-polar InGaN quantum well layer, 543 - Fourth N-polar AlGaN layer with gradient after the well, 544 - Fourth Ga-polar GaN quantum barrier layer. Detailed Implementation

[0059] 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.

[0060] 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.

[0061] See Figures 1 to 2 As shown, this embodiment provides a low operating current density blue Micro-LED epitaxial structure, including a substrate 100, and a buffer layer 200, an N-type semiconductor layer 300, a low-temperature stress relief layer 400, a multi-quantum well light-emitting layer 500 and a P-type semiconductor layer 600 sequentially stacked on the substrate 100, and no electron blocking layer is provided on the multi-quantum well light-emitting layer 500.

[0062] The multi-quantum well light-emitting layer 500 includes a violet multi-quantum well layer 510, a light blue multi-quantum well layer 520, a blue multi-quantum well layer 530 and a violet light quantum well layer 540 stacked sequentially along the epitaxial direction.

[0063] The violet multi-quantum well layer 510, the light blue multi-quantum well layer 520, the blue multi-quantum well layer 530, and the violet end quantum well layer 540 all include N-polar gradient InGaN layer before the well, N-polar InGaN quantum well layer, N-polar gradient AlGaN layer after the well, and Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction.

[0064] The In content of the blue light multi-quantum well layer 530 is greater than that of the light blue light multi-quantum well layer 520, and the In content of the violet light multi-quantum well layer 510 and the violet light light quantum well layer 540 is less than that of the light blue light multi-quantum well layer 520. The blue light multi-quantum well layer 530 is the light-emitting unit of the Micro-LED in this embodiment under low operating current density.

[0065] The N-polar in-well gradient InGaN layer is an N-polar InGaN material with increasing In content along the epitaxial direction, and the N-polar in-well gradient AlGaN layer is an N-polar AlGaN material with decreasing Al content along the epitaxial direction.

[0066] It is worth noting that, based on the above-mentioned structural design of the epitaxial structure of low operating current density blue Micro-LED, the quality of the multi-quantum-well emitting layer can be significantly improved, and the matching degree of electron-hole concentration in the emitting quantum well region can be improved, thereby increasing the radiative recombination efficiency of the emitting quantum well region and thus improving the luminous efficacy of the Micro-LED chip at low operating current density.

[0067] Firstly, in Micro-LEDs, electron leakage has not yet occurred or is very low at low operating current densities. The electron blocking layer structure not only fails to block electrons but also blocks hole injection, reducing the device's radiative recombination efficiency. This embodiment, by omitting the electron blocking layer above the multi-quantum-well light-emitting layer 500, eliminates the blocking effect of the electron blocking layer structure on hole injection, significantly improving the hole injection efficiency of the P-type semiconductor layer 600 and enhancing the matching degree of electron-hole concentration in the multi-quantum-well light-emitting layer 500 region.

[0068] Both are based on the fact that the In content of the blue multi-quantum well layer 530 is greater than that of the light blue multi-quantum well layer 520, which is greater than that of the violet multi-quantum well layer 510 and the violet end-quantum well layer 540. The blue multi-quantum well layer 530 is the light-emitting unit of the Micro-LED in this embodiment at a low operating current density. Since the lower the In content, the higher the growth temperature, the growth temperature of the InGaN material of the violet multi-quantum well layer 510 and the violet end-quantum well layer 540 is greater than that of the InGaN material of the light blue multi-quantum well layer 520, which is greater than that of the InGaN material of the blue multi-quantum well layer 530. The InGaN material of the violet multi-quantum well layer 510 and the violet end-quantum well layer 540 is grown at high temperature, has high atomic mobility, is more inclined to two-dimensional material growth, and the defects in the InGaN material will be significantly reduced, making it easier to obtain high-quality InGaN material. Meanwhile, the In content of the InGaN material in the violet multi-quantum-well layer 510, the light blue multi-quantum-well layer 520, and the violet final quantum-well layer 540 is lower than that in the blue multi-quantum-well layer 530. This reduces the lattice mismatch stress between the multi-quantum-well InGaN material (i.e., the N-polar InGaN quantum-well layer) and the GaN material (i.e., the Ga-polar GaN quantum barrier layer), thus reducing defects caused by large mismatch stress and significantly improving the quality of the multi-quantum-well light-emitting layer 500. The reduced defects in the multi-quantum-well light-emitting layer 500 are beneficial for improving the radiative recombination efficiency of the active region, thereby improving the luminous efficacy and yield of Micro-LEDs at low operating current densities.

[0069] All three, based on the fact that the violet multi-quantum well layer 510, the light blue multi-quantum well layer 520, the blue multi-quantum well layer 530, and the violet end-quantum well layer 540 each include an N-polar gradient InGaN layer before the well, an N-polar InGaN quantum well layer, an N-polar gradient AlGaN layer after the well, and a Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction, make the multi-quantum well light-emitting layer 500 structure designed in this embodiment utilize the fact that the polarization electric field directions of Ga-polar nitride and N-polar nitride are opposite, which can significantly improve the band bending phenomenon caused by the polarization electric field in the multi-quantum well light-emitting layer 500, thereby increasing the coupling degree between the electron and hole wave functions in the quantum well, improving the radiative recombination efficiency in the multi-quantum well light-emitting layer 500, and ultimately improving the luminous efficacy of Micro-LED at low operating current density.

[0070] Fourthly, an N-polar gradient InGaN layer is grown before the N-polar InGaN quantum well layer. The N-polar gradient InGaN layer is an N-polar gradient InGaN material with increasing In content along the epitaxial direction. This structure design can significantly reduce the lattice mismatch stress between the N-polar InGaN quantum well layer and the Ga-polar GaN quantum barrier layer, making it easier to obtain high-quality N-polar InGaN quantum well layer material. Simultaneously, the N-polar gradient AlGaN layers following the growth of the N-polar InGaN quantum well layer are all designed as N-polar gradient AlGaN materials with decreasing Al composition along the epitaxial direction. Specifically, the N-polar gradient AlGaN material is designed with a low Al composition and a low bandgap near the P-type semiconductor layer 600, and a high Al composition and a high bandgap near the N-type semiconductor layer 300. This structural design effectively reduces the blocking effect of the wide bandgap semiconductor AlGaN material on hole injection into the P-type semiconductor layer 600, increases the hole concentration injected into the active region from the P-type semiconductor layer 600, and allows the hole concentration near the N-type semiconductor layer 300 to decrease. The quantum wells in the semiconductor layer 300 can also participate in light emission, significantly improving the matching degree of electron-hole concentration in the multi-quantum-well light-emitting layer 500, and improving the brightness and luminous efficiency of the Micro-LED chip. At the same time, the use of high-Al composition materials with high bandgap near the N-type semiconductor layer 300 can bind electrons in front of the N-polar InGaN quantum well layer material, which can block electrons and reduce electron mobility, improve the radiative recombination efficiency of electrons and holes in the active region, and effectively prevent electron overflow and injection into the P-type semiconductor layer 600 to cause electron leakage, thereby improving the yield and other performance of the Micro-LED chip.

[0071] In some embodiments, the Al content of the N-polar well-tailed gradient AlGaN layer in the violet quantum well layer 540 is less than the Al content of the N-polar well-tailed gradient AlGaN layer in the blue multi-quantum well layer 530 is less than the Al content of the N-polar well-tailed gradient AlGaN layer in the light blue multi-quantum well layer 520 is less than the Al content of the N-polar well-tailed gradient AlGaN layer in the violet multi-quantum well layer 510. Through the aforementioned optimized design, a low-Al composition material with a low bandgap is used near the P-type semiconductor layer 600, while a high-Al composition material with a high bandgap is used near the N-type semiconductor layer 300. This structural design effectively reduces the blocking effect of the wide-bandgap semiconductor AlGaN material on hole injection into the P-type semiconductor layer 600, increases the hole concentration injected into the active region from the P-type semiconductor layer 600, and allows the quantum wells near the N-type semiconductor layer 300 to also participate in light emission. This significantly improves the matching degree of electron-hole concentration in the multi-quantum-well light-emitting layer 500, thereby improving the brightness and luminous efficacy of the Micro-LED chip. Simultaneously, the use of a high-Al composition material with a high bandgap near the N-type semiconductor layer 300 can bind electrons in front of the N-polar InGaN quantum well layer material, blocking electrons and reducing their migration speed. This improves the radiative recombination efficiency of electrons and holes in the active region and effectively prevents electron overflow and injection into the P-type semiconductor layer 600, thus improving the yield and other performance characteristics of the Micro-LED chip.

[0072] In some embodiments, the In content of the N-polar gradient InGaN layer in the blue multi-quantum well layer 530 is greater than or equal to the In content of the N-polar gradient InGaN layer in the light blue multi-quantum well layer 520; and the In content of the N-polar gradient InGaN layer in the violet multi-quantum well layer 510 and the violet final quantum well layer 540 is less than or equal to the In content of the N-polar gradient InGaN layer in the light blue multi-quantum well layer 520. Through the above structural optimization, it is beneficial to further improve the quality of the multi-quantum well light-emitting layer 500, thereby further improving the luminous efficacy and yield of Micro-LED at low operating current density.

[0073] In some embodiments, the In content of the N-polar InGaN quantum well layer in the purple light multi-quantum well layer 510 is Y1;

[0074] The In composition content of the N-polar InGaN quantum well layer in the light blue light multi-quantum well layer 520 is Y2;

[0075] The In composition content of the N-polar InGaN quantum well layer in the blue light multi-quantum well layer 530 is Y3;

[0076] The In composition content of the N-polar InGaN quantum well layer 540 in the purple light-emitting quantum well layer is Y4;

[0077] Where Y1 < Y2 < Y3, and Y4 < Y2.

[0078] Based on the above optimized design, the N-polar InGaN quantum well layer of the multi-quantum well emitting layer 500 forms an InGaN / barrier superlattice structure with the In content first increasing and then decreasing. This structure and process design can effectively reduce the lattice mismatch stress between the blue quantum well InGaN material (i.e., the third N-polar InGaN quantum well layer 532) and the barrier material (i.e., the third Ga-polar GaN quantum barrier layer 534), improve the quality of the low operating current density emitting quantum well region (i.e., the blue multi-quantum well layer 530), and thus further improve the radiative recombination efficiency of the active region.

[0079] Furthermore, the In content of the N-polar InGaN quantum well layers in the violet multi-quantum well layer 510, light blue multi-quantum well layer 520, and violet end quantum well layer 540 is lower than that in the blue multi-quantum well layer 530. This results in a reduction of the lattice mismatch stress between the InGaN material (N-polar InGaN quantum well layer) and the GaN material (Ga-polar GaN quantum barrier layer) in the violet multi-quantum well layer 510, light blue multi-quantum well layer 520, and violet end quantum well layer 540. The reduction of defects caused by large mismatch stress can significantly improve the quality of the multi-quantum well light-emitting layer 500. The reduction of defects in the multi-quantum well light-emitting layer 500 is beneficial to improving the radiative recombination efficiency of the active region, thereby improving the luminous efficacy and yield of Micro-LEDs at low operating current densities.

[0080] In some embodiments, the N-polar gradient InGaN layer before the quantum well of the violet multi-quantum-well layer 510 is a first N-polar gradient InGaN layer before the quantum well 511. Along the epitaxial direction, the In content of the first N-polar gradient InGaN layer before the quantum well 511 increases from Y11 to Y12, where 0 ≤ Y11 ≤ 0.02, 0.10 ≤ Y12 ≤ 0.14. Specifically, Y11 is exemplarily 0, 0.01, or 0.02, and Y12 is exemplarily 0.10, 0.11, 0.12, 0.13, or 0.14, but is not limited thereto. The first N-polar gradient InGaN layer before the quantum well 511 is doped with Si, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm 3 ~6.75×10 17 / cm 3 The growth thickness is 0.1nm~0.8nm, the growth temperature is 775℃~920℃, and the pressure is 50torr~360torr.

[0081] In some embodiments, the N-polar InGaN quantum well layer 510 of the violet light multi-quantum well layer is a first N-polar InGaN quantum well layer 512. The first N-polar InGaN quantum well layer 512 is a single-layer or multi-layer structure of high-In-content N-polar InGaN without intentional doping. The In content of the first N-polar InGaN quantum well layer 512 is Y1, wherein 0.10 ≤ Y1 ≤ 0.14. Specifically, Y1 is exemplarily 0.10, 0.11, 0.12, 0.13, or 0.14, but is not limited thereto. The growth thickness of the first N-polar InGaN quantum well layer 512 is 2.1 nm to 4.8 nm, the growth temperature is 775 °C to 920 °C, and the pressure is 50 torr to 360 torr.

[0082] In some embodiments, the N-polar well-followed gradient AlGaN layer of the violet multi-quantum well layer 510 is a first N-polar well-followed gradient AlGaN layer 513; along the epitaxial direction, the Al content of the first N-polar well-followed gradient AlGaN layer 513 decreases from X11 to X12, wherein 0.08 < X11 ≤ 0.25, 0 ≤ X12 ≤ 0.08. Specifically, X11 is exemplarily 0.09, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22 or 0.25, and X12 is exemplarily 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07 or 0.08, but is not limited thereto. The first N-polar well followed by the gradient AlGaN layer 513 has a growth thickness of 0.1 nm to 0.8 nm, a growth temperature of 780 °C to 930 °C, and a pressure of 50 torr to 360 torr.

[0083] In some embodiments, the N-polar gradient InGaN layer before the light blue quantum well layer 520 is a second N-polar gradient InGaN layer before the well 521. Along the epitaxial direction, the In content of the second N-polar gradient InGaN layer before the well 521 increases from Y21 to Y22, where 0 ≤ Y21 ≤ 0.03, 0.14 ≤ Y22 ≤ 0.16. Specifically, Y21 is exemplarily 0, 0.01, 0.02, or 0.03, and Y22 is exemplarily 0.14, 0.15, or 0.16, but is not limited thereto. The second N-polar gradient InGaN layer before the well 521 is doped with Si, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm 3 ~6.75×10 17 / cm 3 The growth thickness is 0.1nm~0.8nm, the growth temperature is 760℃~920℃, and the pressure is 50torr~360torr.

[0084] In some embodiments, the N-polar InGaN quantum well layer 520 of the light blue light multi-quantum well layer is a second N-polar InGaN quantum well layer 522. The second N-polar InGaN quantum well layer 522 is a single-layer or multi-layer structure of high-In-content N-polar InGaN without intentional doping. The In content of the second N-polar InGaN quantum well layer 522 is Y2, wherein 0.14 ≤ Y2 ≤ 0.16. Specifically, Y2 is exemplarily 0.14, 0.15, or 0.16, but is not limited thereto. The growth thickness of the second N-polar InGaN quantum well layer 522 is 2.1 nm to 4.8 nm, the growth temperature is 760 °C to 920 °C, and the pressure is 50 torr to 360 torr.

[0085] In some embodiments, the N-polar well-followed graded AlGaN layer of the light blue multi-quantum well layer 520 is a second N-polar well-followed graded AlGaN layer 523; along the epitaxial direction, the Al content of the second N-polar well-followed graded AlGaN layer 523 decreases from X21 to X22, wherein 0.06 < X21 ≤ 0.21, 0 ≤ X22 ≤ 0.06. Specifically, X21 is exemplarily 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or 0.21, but is not limited thereto. X22 is exemplarily 0, 0.01, 0.02, 0.03, 0.04, 0.05, or 0.06, but is not limited thereto. The growth thickness of the second N-polar well-graded AlGaN layer 523 is 0.1 nm to 0.8 nm, the growth temperature is 780 °C to 930 °C, and the pressure is 50 torr to 360 torr.

[0086] In some embodiments, the N-polar gradient InGaN layer before the blue quantum well layer 530 is a third N-polar gradient InGaN layer 531; along the epitaxial direction, the In content of the third N-polar gradient InGaN layer 531 increases from Y31 to Y32, wherein 0 ≤ Y31 ≤ 0.05, 0.16 ≤ Y32 ≤ 0.19. Specifically, Y31 is exemplarily 0, 0.01, 0.02, 0.03, 0.04, or 0.05, but is not limited thereto. Y32 is exemplarily 0.16, 0.17, 0.18, or 0.19, but is not limited thereto. The third N-polar gradient InGaN layer 531 is doped with Si element, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm 3 ~6.75×10 17 / cm 3The growth thickness is 0.1nm~0.8nm, the growth temperature is 750℃~920℃, and the pressure is 50torr~360torr.

[0087] The N-polar InGaN quantum well layer 530 of the blue light multi-quantum well layer is a third N-polar InGaN quantum well layer 532. The third N-polar InGaN quantum well layer 532 is a single-layer or multi-layer structure of high-In-content N-polar InGaN without intentional doping. The In content of the third N-polar InGaN quantum well layer 532 is Y3, wherein 0.16≤Y3≤0.19. Specifically, Y3 is exemplarily 0.16, 0.17, 0.18, or 0.19, but is not limited thereto. The growth thickness of the third N-polar InGaN quantum well layer 532 is 2.1nm~4.8nm, the growth temperature is 750℃~920℃, and the pressure is 50torr~360torr.

[0088] The N-polar well-followed graded AlGaN layer of the blue light multi-quantum well layer 530 is a third N-polar well-followed graded AlGaN layer 533; along the epitaxial direction, the Al content of the third N-polar well-followed graded AlGaN layer 533 decreases from X31 to X32, wherein 0.05 < X31 ≤ 0.18, 0 ≤ X32 ≤ 0.05. Specifically, X31 is exemplarily 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17 or 0.18, and X32 is exemplarily 0, 0.01, 0.02, 0.03, 0.04 or 0.05, but is not limited thereto. The growth thickness of the third N-polar well-graded AlGaN layer 533 is 0.1 nm to 0.8 nm, the growth temperature is 780 °C to 930 °C, and the pressure is 50 torr to 360 torr.

[0089] In some embodiments, the N-polar gradient InGaN layer before the quantum well layer 540 is a fourth N-polar gradient InGaN layer 541; along the epitaxial direction, the In content of the fourth N-polar gradient InGaN layer 541 increases from Y41 to Y42, wherein 0 ≤ Y41 ≤ 0.02, 0.10 ≤ Y42 ≤ 0.14. Specifically, Y41 is exemplarily 0, 0.01, or 0.02, and Y42 is exemplarily 0.10, 0.11, 0.12, 0.13, or 0.14, but is not limited thereto. The fourth N-polar gradient InGaN layer 541 is doped with Si, and the Si doping concentration is 1.12 × 10⁻⁶. 17 / cm 3 ~6.75×10 17 / cm 3The growth thickness is 0.1nm~0.8nm, the growth temperature is 775℃~920℃, and the pressure is 50torr~360torr.

[0090] In some embodiments, the N-polar InGaN quantum well layer 540 of the ultraviolet-emitting quantum well layer 540 is a fourth N-polar InGaN quantum well layer 542. The fourth N-polar InGaN quantum well layer 542 is a single-layer or multi-layer structure of high-In-content N-polar InGaN without intentional doping. The In content of the fourth N-polar InGaN quantum well layer 542 is Y4, wherein 0.10 ≤ Y4 ≤ 0.14. Specifically, Y4 is exemplary to be 0.10, 0.11, 0.12, 0.13 or 0.14, but is not limited thereto. The growth thickness of the fourth N-polar InGaN quantum well layer 542 is 2.1 nm to 4.8 nm, the growth temperature is 775 °C to 920 °C, and the pressure is 50 torr to 360 torr.

[0091] In some embodiments, the N-polar well-tailed gradient AlGaN layer of the violet-light quantum well layer 540 is a fourth N-polar well-tailed gradient AlGaN layer 543; along the epitaxial direction, the Al content of the fourth N-polar well-tailed gradient AlGaN layer 543 decreases from X41 to X42, wherein 0.03 < X41 ≤ 0.15, 0 ≤ X42 ≤ 0.03; specifically, X41 is exemplarily 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14 or 0.15, and X42 is exemplarily 0, 0.01, 0.02 or 0.03, but is not limited thereto. The growth thickness of the fourth N-polar well-graded AlGaN layer 543 is 0.1 nm to 0.8 nm, the growth temperature is 780 °C to 930 °C, and the pressure is 50 torr to 360 torr.

[0092] In some embodiments, X41≤X31≤X21≤X11, and X42≤X32≤X22≤X12, so that the Al component content of the fourth N-polar well-followed gradient AlGaN layer 543 is ≤ the Al component content of the third N-polar well-followed gradient AlGaN layer 533 is ≤ the Al component content of the second N-polar well-followed gradient AlGaN layer 523 is ≤ the Al component content of the first N-polar well-followed gradient AlGaN layer 513.

[0093] In some embodiments, Y31≥Y21≥Y11 / Y41, and Y32≥Y22≥Y12 / Y42, so that the In content of the third N-polar gradient InGaN layer 531 is ≥ the In content of the second N-polar gradient InGaN layer 521 is ≥ the In content of the first N-polar gradient InGaN layer 511 and the fourth N-polar gradient InGaN layer 541.

[0094] In some embodiments, the growth temperature of the N-polar gradient InGaN layer in the violet multi-quantum well layer 510 and the violet end-quantum well layer 540 is ≥ the growth temperature of the N-polar gradient InGaN layer in the light blue multi-quantum well layer 520 is ≥ the growth temperature of the N-polar gradient InGaN layer in the blue multi-quantum well layer 530.

[0095] In some embodiments, the growth temperature of the first N-polar gradient InGaN layer 511 before the well is 775°C to 920°C, the growth temperature of the second N-polar gradient InGaN layer 521 before the well is 760°C to 920°C, the growth temperature of the third N-polar gradient InGaN layer 531 before the well is 750°C to 920°C, and the growth temperature of the fourth N-polar gradient InGaN layer 541 before the well is 775°C to 920°C.

[0096] In some embodiments, the Ga polar GaN quantum barrier layers in the violet multi-quantum well layer 510, the light blue multi-quantum well layer 520, the blue multi-quantum well layer 530, and the violet final quantum well layer 540 are respectively a first Ga polar GaN quantum barrier layer 514, a second Ga polar GaN quantum barrier layer 524, a third Ga polar GaN quantum barrier layer 534, and a fourth Ga polar GaN quantum barrier layer 544;

[0097] The first Ga-polar GaN quantum barrier layer 514, the second Ga-polar GaN quantum barrier layer 524, the third Ga-polar GaN quantum barrier layer 534, and the fourth Ga-polar GaN quantum barrier layer 544 are all Ga-polar GaN materials doped with Si, and their growth thicknesses are all 6nm to 13nm, exemplarily 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, or 13nm, but not limited to these; the Si doping concentration is all 2.15×10⁻⁶. 17 / cm 3 ~8.79×10 17 / cm 3 For example, it is 2.15 × 10 17 / cm 3 2.5×10 17 / cm 3 3×10 17 / cm 3 3.5×10 17 / cm 3 4×10 17 / cm 3 4.5×10 17 / cm 3 5×10 17 / cm 3 5.5×10 17 / cm 3 6×10 17 / cm 3 6.5×10 17 / cm 3 7×10 17 / cm 3 8.5×10 17 / cm 3 Or 8.79×10 17 / cm 3 However, the growth temperature is not limited to 820℃~935℃, exemplarily 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃ or 935℃, but not limited to 820℃; the pressure is not limited to 50 torr~360 torr, exemplarily 50 torr, 100 torr, 120 torr, 150 torr, 180 torr, 200 torr, 220 torr, 250 torr, 280 torr, 300 torr, 330 torr or 360 torr, but not limited to 50 torr. It is worth noting that the growth thickness, Si doping concentration, growth temperature, and pressure of the first Ga polar GaN quantum barrier layer 514, the second Ga polar GaN quantum barrier layer 524, the third Ga polar GaN quantum barrier layer 534, and the fourth Ga polar GaN quantum barrier layer 544 can be the same or different, as long as they are within the above range.

[0098] In some embodiments, the number of alternating growth cycles of the violet multi-quantum well layer 510 is 1 to 3, exemplarily 1, 2, or 3, but not limited thereto; the number of alternating growth cycles of the light blue multi-quantum well layer 520 is 1 to 5, exemplarily 1, 2, 3, 4, or 5, but not limited thereto; the number of alternating growth cycles of the blue multi-quantum well layer 530 is 2 to 8, exemplarily 2, 3, 4, 5, 6, 7, or 8, but not limited thereto; and the number of alternating growth cycles of the violet final quantum well layer 540 is 1 to 3, exemplarily 1, 2, or 3, but not limited thereto.

[0099] Specifically, the substrate 100 in this embodiment is selected from commonly used substrates in the art, such as sapphire substrates. The buffer layer 200, N-type semiconductor layer 300, low-temperature stress relief layer 400 and P-type semiconductor layer 600 in this embodiment are all prepared using existing processes and materials, and will not be further described in this technical solution.

[0100] Accordingly, a method for fabricating a low-current-density blue Micro-LED epitaxial structure is also provided, comprising the following steps:

[0101] (1) Select substrate 100;

[0102] (2) A buffer layer 200 is grown on the substrate 100;

[0103] (3) Introduce a Si doping source and grow an N-type semiconductor layer 300 on the buffer layer 200;

[0104] (4) A low-temperature stress relief layer 400 is grown on the N-type semiconductor layer 300;

[0105] (5) A multi-quantum well light-emitting layer 500 is grown on the low-temperature stress relief layer 400;

[0106] (6) A P-type semiconductor layer 600 is grown on the multi-quantum-well light-emitting layer 500;

[0107] The multi-quantum-well light-emitting layer 500 includes a violet multi-quantum-well layer 510, a light blue multi-quantum-well layer 520, a blue multi-quantum-well layer 530, and a violet end-quantum-well layer 540 stacked sequentially along the epitaxial direction; the In content of the blue multi-quantum-well layer 530 is greater than the In content of the light blue multi-quantum-well layer 520, and the In content of both the violet multi-quantum-well layer 510 and the violet end-quantum-well layer 540 is less than the In content of the light blue multi-quantum-well layer 520.

[0108] The violet multi-quantum well layer 510, the light blue multi-quantum well layer 520, the blue multi-quantum well layer 530, and the violet end-quantum well layer 540 all include N-polar gradient InGaN layer before the well, N-polar InGaN quantum well layer, N-polar gradient AlGaN layer after the well, and Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction.

[0109] The N-polar well-before gradient InGaN layer is an N-polar InGaN material with increasing In content along the epitaxial direction, and the N-polar well-before gradient AlGaN layer is an N-polar AlGaN material with decreasing Al content along the epitaxial direction.

[0110] After the N-polar InGaN quantum well layers of the light blue multi-quantum well layer 520 and the violet-light final quantum well layer 540 are periodically deposited and grown alternately, the surface of the epitaxial layer material needs to be annealed. Specifically, after the deposition and growth of the second N-polar InGaN quantum well layer 522 and the fourth N-polar InGaN quantum well layer 542, H2 needs to be intermittently and cyclically introduced into the reaction chamber and stabilized for 5s to 90s. After H2 annealing, defects such as poor crystal quality materials and high-In-content In clusters on the surface of the material will be decomposed, which is beneficial to improving the crystal quality of the material. At the same time, a slightly rough surface is formed, which can reduce the in-plane total internal reflection and light absorption loss of photons in the semiconductor material and improve the light extraction efficiency. In some embodiments, the temperature of H2 annealing is 820℃ to 1080℃, and the pressure is 30 torr to 600 torr.

[0111] This embodiment utilizes a surface roughening treatment technique involving hydrogen annealing to further improve the luminous efficacy of Micro-LEDs at low operating current densities. In summary, the redesign of the epitaxial structure for small-size, low-current, and low-power Micro-LEDs, compared to the structure and process design of multi-quantum-well emissive layers with the same emission wavelength, significantly improves the quality of the multi-quantum-well emissive layer and the matching degree of electron-hole concentration in the luminous quantum well region, thereby increasing the radiative recombination efficiency of the luminous quantum well region and ultimately enhancing the luminous efficacy of the Micro-LED chip at low operating current densities.

[0112] The technical solution of the present invention will be further described below through embodiments and comparative examples.

[0113] Example 1

[0114] This embodiment provides a low operating current density blue Micro-LED epitaxial structure, including a substrate 100, and further including a buffer layer 200, an N-type semiconductor layer 300, a low-temperature stress relief layer 400, a multi-quantum well light-emitting layer 500 and a P-type semiconductor layer 600 sequentially stacked on the substrate 100, and no electron blocking layer is provided on the multi-quantum well light-emitting layer 500.

[0115] The multi-quantum well light-emitting layer 500 includes a violet multi-quantum well layer 510, a light blue multi-quantum well layer 520, a blue multi-quantum well layer 530 and a violet light quantum well layer 540 stacked sequentially along the epitaxial direction.

[0116] The purple-light multi-quantum-well layer 510 includes a first N-polar gradient InGaN layer 511, a first N-polar InGaN quantum well layer 512, a first N-polar gradient AlGaN layer 513, and a first Ga-polar GaN quantum barrier layer 514, which are periodically and alternately grown along the epitaxial direction. Specifically, along the epitaxial direction, the In content of the first N-polar gradient InGaN layer 511 increases from Y11 to Y12, where Y11 is 0 and Y12 is 0.10; the In content of the first N-polar InGaN quantum well layer 512 is Y1, where Y1 is 0.10; and the Al content of the first N-polar gradient AlGaN layer 513 decreases from X11 to X12 along the epitaxial direction, where X11 is 0.25 and X12 is 0.08.

[0117] The light blue multi-quantum-well layer 520 includes a second N-polarity gradient InGaN layer 521, a second N-polarity InGaN quantum well layer 522, a second N-polarity gradient AlGaN layer 523, and a second Ga-polarity GaN quantum barrier layer 524, which are periodically and alternately grown along the epitaxial direction. Along the epitaxial direction, the In content of the second N-polarity gradient InGaN layer 521 increases from Y21 to Y22, where Y21 is 0.01 and Y22 is 0.14. The In content of the second N-polarity InGaN quantum well layer 522 is Y2, where Y2 is 0.14. Along the epitaxial direction, the Al content of the second N-polarity gradient AlGaN layer 523 decreases from X21 to X22, where X21 is 0.21 and X22 is 0.06.

[0118] The blue light multi-quantum-well layer 530 includes a third N-polarity gradient InGaN layer 531, a third N-polarity InGaN quantum well layer 532, a third N-polarity gradient AlGaN layer 533, and a third Ga-polarity GaN quantum barrier layer 534, which are periodically and alternately grown along the epitaxial direction. Specifically, along the epitaxial direction, the In content of the third N-polarity gradient InGaN layer 531 increases from Y31 to Y32, where Y31 is 0.03 and Y32 is 0.16; the In content of the third N-polarity InGaN quantum well layer 532 is Y3, where Y3 is 0.16; and along the epitaxial direction, the Al content of the third N-polarity gradient AlGaN layer 533 decreases from X31 to X32, where X31 is 0.18 and X32 is 0.05.

[0119] The quantum well layer 540 includes a fourth N-polarity gradient InGaN layer 541, a fourth N-polarity InGaN quantum well layer 542, a fourth N-polarity gradient AlGaN layer 543, and a fourth Ga-polarity GaN quantum barrier layer 544, which are periodically and alternately grown along the epitaxial direction. Specifically, along the epitaxial direction, the In content of the fourth N-polarity gradient InGaN layer 541 increases from Y41 to Y42, where Y41 is 0 and Y42 is 0.10; the In content of the fourth N-polarity InGaN quantum well layer 542 is Y4, where Y4 is 0.10; and along the epitaxial direction, the Al content of the fourth N-polarity gradient AlGaN layer 543 decreases from X41 to X42, where X41 is 0.15 and X42 is 0.03.

[0120] In this embodiment, Y1 < Y2 < Y3, and Y4 < Y2; X41 < X31 < X21 < X11, and X42 < X32 < X22 < X12; Y31 > Y21 > Y11 = Y41, and Y32 > Y22 > Y12 = Y42;

[0121] The first Ga-polar GaN quantum barrier layer 514, the second Ga-polar GaN quantum barrier layer 524, the third Ga-polar GaN quantum barrier layer 534, and the fourth Ga-polar GaN quantum barrier layer 544 are all Ga-polar GaN materials doped with Si, with a growth thickness of 8 nm and a Si doping concentration of 5 × 10⁻⁶. 17 / cm 3 The growth temperature was 850℃ and the pressure was 120 torr.

[0122] The number of alternating growth cycles for the violet multi-quantum well layer 510 is 2, the number of alternating growth cycles for the light blue multi-quantum well layer 520 is 2, the number of alternating growth cycles for the blue multi-quantum well layer 530 is 6, and the period range for the alternating growth of the violet final quantum well layer 540 is 2.

[0123] The method for fabricating a low-current-density blue Micro-LED epitaxial structure in this embodiment includes the following steps:

[0124] (1) Select substrate 100; (2) Grow a buffer layer 200 on substrate 100; (3) Introduce a Si doping source and grow an N-type semiconductor layer 300 on buffer layer 200; (4) Grow a low-temperature stress relief layer 400 on N-type semiconductor layer 300; (5) Grow a multi-quantum well light-emitting layer 500 on low-temperature stress relief layer 400; (6) Grow a P-type semiconductor layer 600 on multi-quantum well light-emitting layer 500.

[0125] After the periodic alternating deposition and growth of the second N-polar InGaN quantum well layer 522 and the fourth N-polar InGaN quantum well layer 542, annealing treatment is required on the surface of the epitaxial layer material.

[0126] Example 2

[0127] This embodiment provides a low operating current density blue Micro-LED epitaxial structure, which is basically the same as that in Embodiment 1, except that:

[0128] In Example 2, along the epitaxial direction, the In content of the first N-polarity gradient InGaN layer 511 increases from Y11 to Y12, where Y11 is 0.01 and Y12 is 0.12; the In content of the first N-polarity InGaN quantum well layer 512 is Y1, where Y1 is 0.12; the Al content of the first N-polarity gradient AlGaN layer 513 decreases from X11 to X12 along the epitaxial direction, where X11 is 0.18 and X12 is 0.05.

[0129] Along the epitaxial direction, the In content of the gradient InGaN layer 521 before the second N-polar well increases from Y21 to Y22, where Y21 is 0.02 and Y22 is 0.15; the In content of the second N-polar InGaN quantum well layer 522 is Y2, where Y2 is 0.15; along the epitaxial direction, the Al content of the gradient AlGaN layer 523 after the second N-polar well decreases from X21 to X22, where X21 is 0.15 and X22 is 0.04.

[0130] Along the epitaxial direction, the In content of the third N-polarity in-well gradient InGaN layer 531 increases from Y31 to Y32, where Y31 is 0.04 and Y32 is 0.18; the In content of the third N-polarity inGaN quantum well layer 532 is Y3, where Y3 is 0.18; along the epitaxial direction, the Al content of the third N-polarity in-well gradient AlGaN layer 533 decreases from X31 to X32, where X31 is 0.12 and X32 is 0.03.

[0131] Along the epitaxial direction, the In content of the fourth N-polar InGaN quantum well layer 541 increases from Y41 to Y42, where Y41 is 0.01 and Y42 is 0.12; the In content of the fourth N-polar InGaN quantum well layer 542 is Y4, where Y4 is 0.12; along the epitaxial direction, the Al content of the fourth N-polar InGaN quantum well layer 543 decreases from X41 to X42, where X41 is 0.10 and X42 is 0.02.

[0132] In this embodiment, Y4 = Y1 < Y2 < Y3; X41 < X31 < X21 < X11, and X42 < X32 < X22 < X12; Y31 > Y21 > Y11 = Y41, and Y32 > Y22 > Y12 = Y42.

[0133] Example 3

[0134] This embodiment provides a low operating current density blue Micro-LED epitaxial structure, which is basically the same as that in Embodiment 1, except that:

[0135] In Example 3, along the epitaxial direction, the In content of the first N-polarity gradient InGaN layer 511 before the first N-polarity well increases from Y11 to Y12, where Y11 is 0.02 and Y12 is 0.14; the In content of the first N-polarity InGaN quantum well layer 512 is Y1, where Y1 is 0.14; the Al content of the first N-polarity gradient AlGaN layer 513 after the first N-polarity well decreases from X11 to X12 along the epitaxial direction, where X11 is 0.12 and X12 is 0.04.

[0136] Along the epitaxial direction, the In content of the gradient InGaN layer 521 before the second N-polar well increases from Y21 to Y22, where Y21 is 0.03 and Y22 is 0.16; the In content of the second N-polar InGaN quantum well layer 522 is Y2, where Y2 is 0.16; along the epitaxial direction, the Al content of the gradient AlGaN layer 523 after the second N-polar well decreases from X21 to X22, where X21 is 0.10 and X22 is 0.03.

[0137] Along the epitaxial direction, the In content of the third N-polarity in-well gradient InGaN layer 531 increases from Y31 to Y32, where Y31 is 0.05 and Y32 is 0.19; the In content of the third N-polarity inGaN quantum well layer 532 is Y3, where Y3 is 0.19; along the epitaxial direction, the Al content of the third N-polarity in-well gradient AlGaN layer 533 decreases from X31 to X32, where X31 is 0.09 and X32 is 0.02.

[0138] Along the epitaxial direction, the In content of the fourth N-polar InGaN quantum well layer 541 increases from Y41 to Y42, where Y41 is 0.02 and Y42 is 0.14; the In content of the fourth N-polar InGaN quantum well layer 542 is Y4, where Y4 is 0.14; along the epitaxial direction, the Al content of the fourth N-polar InGaN quantum well layer 543 decreases from X41 to X42, where X41 is 0.06 and X42 is 0.01.

[0139] In this embodiment, Y4 = Y1 < Y2 < Y3; X41 < X31 < X21 < X11, and X42 < X32 < X22 < X12; Y31 > Y21 > Y11 = Y41, and Y32 > Y22 > Y12 = Y42.

[0140] Comparative Example 1

[0141] This comparative example provides a low operating current density blue Micro-LED epitaxial structure. The difference between this comparative example and Example 1 is that the multi-quantum well light-emitting layer in this comparative example only has a blue multi-quantum well layer, and does not have a violet multi-quantum well layer, a light blue multi-quantum well layer, or a violet end-quantum well layer; the number of cycles of the blue multi-quantum well layer is 12.

[0142] Comparative Example 2

[0143] This comparative example provides a low operating current density blue Micro-LED epitaxial structure, which is basically the same as that of Example 1, except that: in Comparative Example 2, the In content of the first N-polar well-prefixed InGaN layer remains consistent at 0.5; the In content of the second N-polar well-prefixed InGaN layer remains consistent at 0.8; the In content of the third N-polar well-prefixed InGaN layer remains consistent at 0.10; and the In content of the fourth N-polar well-prefixed InGaN layer remains consistent at 0.5.

[0144] Comparative Example 3

[0145] This comparative example provides a low operating current density blue Micro-LED epitaxial structure, which is basically the same as that of Example 1, except that the Al composition content of the first N-polar well-graded AlGaN layer, the second N-polar well-graded AlGaN layer, the third N-polar well-graded AlGaN layer, and the fourth N-polar well-graded AlGaN layer in Comparative Example 3 is consistent, all being 0.18.

[0146] Performance testing:

[0147] The Micro-LED epitaxial structures obtained in Examples 1-3 and Comparative Examples 1-3 were fabricated into 20μm×20μm Micro-LED chips using the same chip fabrication conditions. Their luminous efficiency was tested at an operating current of 0.5μA. Based on Comparative Example 1, the luminous efficiency improvement rate in each example and comparative example was calculated.

[0148] Light efficiency improvement rate = (Improved light efficiency - Original light efficiency) / Original light efficiency × 100%;

[0149] In the above calculation formula: the original light effect is the same as the light effect of Comparative Example 1.

[0150] Specifically, the test results are shown in Table 1 below:

[0151] Table 1 Performance Test Results

[0152]

[0153] As can be seen from Table 1, the structural design of the epitaxial structure of the low operating current density blue Micro-LED of the present invention can significantly improve the quality of the multi-quantum well light-emitting layer, improve the matching degree of electron-hole concentration in the light-emitting quantum well region, and improve the radiative recombination efficiency in the light-emitting quantum well region, thereby improving the luminous efficacy of the Micro-LED chip at low operating current density.

[0154] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A low operating current density blue Micro-LED epitaxial structure, comprising a substrate, characterized in that, It also includes a buffer layer, an N-type semiconductor layer, a low-temperature stress relief layer, a multi-quantum well light-emitting layer and a P-type semiconductor layer stacked sequentially on the substrate, and no electron blocking layer is provided above the multi-quantum well light-emitting layer; The multi-quantum-well light-emitting layer includes a violet multi-quantum-well layer, a light blue multi-quantum-well layer, a blue multi-quantum-well layer, and a violet final quantum-well layer, which are stacked sequentially along the epitaxial direction. The violet multi-quantum well layer, the light blue multi-quantum well layer, the blue multi-quantum well layer, and the violet end-quantum well layer all include N-polar gradient InGaN layer before the well, N-polar InGaN quantum well layer, N-polar gradient AlGaN layer after the well, and Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction. The In content of the blue light multi-quantum well layer is greater than that of the light blue light multi-quantum well layer, and the In content of both the violet light multi-quantum well layer and the violet light end-quantum well layer is less than that of the light blue light multi-quantum well layer. The N-polar well-before gradient InGaN layer is an N-polar InGaN material with increasing In content along the epitaxial direction, and the N-polar well-before gradient AlGaN layer is an N-polar AlGaN material with decreasing Al content along the epitaxial direction. The Al content of the N-polar well-tailed gradient AlGaN layer in the violet-light quantum well layer is less than or equal to the Al content of the N-polar well-tailed gradient AlGaN layer in the blue-light multi-quantum well layer. The Al content of the N-polar well-tailed gradient AlGaN layer in the light-blue-light multi-quantum well layer is less than or equal to the Al content of the N-polar well-tailed gradient AlGaN layer in the violet-light multi-quantum well layer.

2. The low operating current density blue Micro-LED epitaxial structure according to claim 1, characterized in that, The In content of the N-polar gradient InGaN layer in the blue light multi-quantum well layer is greater than or equal to the In content of the N-polar gradient InGaN layer in the light blue light multi-quantum well layer. The In content of the N-polar gradient InGaN layer in the violet multi-quantum well layer and the violet end quantum well layer is less than or equal to the In content of the N-polar gradient InGaN layer in the light blue multi-quantum well layer.

3. The low operating current density blue Micro-LED epitaxial structure according to claim 1, characterized in that, The In composition content of the N-polar InGaN quantum well layer in the purple light multi-quantum well layer is Y1; The In component content of the N-polar InGaN quantum well layer in the light blue light multi-quantum well layer is Y2; The In component content of the N-polar InGaN quantum well layer in the blue light multi-quantum well layer is Y3; The In composition content of the N-polar InGaN quantum well layer in the purple light-emitting quantum well layer is Y4; Where Y1 < Y2 < Y3, and Y4 < Y2.

4. The low operating current density blue Micro-LED epitaxial structure according to claim 1, characterized in that, The N-polar gradient InGaN layer before the well, the N-polar InGaN quantum well layer, and the N-polar gradient AlGaN layer after the well in the purple light multi-quantum well layer are respectively the first N-polar gradient InGaN layer before the well, the first N-polar InGaN quantum well layer, and the first N-polar gradient AlGaN layer after the well. Along the epitaxial direction, the In composition content of the first N-polar well-preceded gradient InGaN layer increases from Y11 to Y12, where 0≤Y11≤0.02 and 0.10≤Y12≤0.

14. The In composition content of the first N-polar InGaN quantum well layer is Y1, wherein 0.10≤Y1≤0.14; Along the epitaxial direction, the Al composition content of the first N-polar well-derived graded AlGaN layer decreases from X11 to X12, where 0.08 < X11 ≤ 0.25 and 0 ≤ X12 ≤ 0.

08.

5. The low operating current density blue Micro-LED epitaxial structure according to claim 4, characterized in that, The N-polar gradient InGaN layer before the light blue light multi-quantum well layer, the N-polar InGaN quantum well layer, and the N-polar gradient AlGaN layer after the N-polar well are respectively the second N-polar gradient InGaN layer before the N-polar well, the second N-polar InGaN quantum well layer, and the second N-polar gradient AlGaN layer after the N-polar well. Along the epitaxial direction, the In composition content of the second N-polar well-precessed gradient InGaN layer increases from Y21 to Y22, where 0≤Y21≤0.03 and 0.14≤Y22≤0.

16. The In composition content of the second N-polar InGaN quantum well layer is Y2, wherein 0.14≤Y2≤0.16; Along the epitaxial direction, the Al composition content of the second N-polar well-followed gradient AlGaN layer decreases from X21 to X22, where 0.06 < X21 ≤ 0.21 and 0 ≤ X22 ≤ 0.

06.

6. The low operating current density blue Micro-LED epitaxial structure according to claim 5, characterized in that, The N-polar gradient InGaN layer before the well, the N-polar InGaN quantum well layer, and the N-polar gradient AlGaN layer after the well in the blue light multi-quantum well layer are respectively the third N-polar gradient InGaN layer before the well, the third N-polar InGaN quantum well layer, and the third N-polar gradient AlGaN layer after the well. Along the epitaxial direction, the In composition content of the third N-polar well-preceded gradient InGaN layer increases from Y31 to Y32, where 0≤Y31≤0.05 and 0.16≤Y32≤0.

19. The In composition of the third N-polar InGaN quantum well layer is Y3, wherein 0.16≤Y3≤0.19; Along the epitaxial direction, the Al composition content of the third N-polar well-followed gradient AlGaN layer decreases from X31 to X32, where 0.05 < X31 ≤ 0.18 and 0 ≤ X32 ≤ 0.

05.

7. The low operating current density blue Micro-LED epitaxial structure according to claim 6, characterized in that, The N-polar gradient InGaN layer before the quantum well, the N-polar InGaN quantum well layer, and the N-polar gradient AlGaN layer after the quantum well are respectively the fourth N-polar gradient InGaN layer before the quantum well, the fourth N-polar InGaN quantum well layer, and the fourth N-polar gradient AlGaN layer after the quantum well. Along the epitaxial direction, the In composition content of the fourth N-polar well-precessed gradient InGaN layer increases from Y41 to Y42, where 0≤Y41≤0.02 and 0.10≤Y42≤0.

14. The In composition of the fourth N-polar InGaN quantum well layer is Y4, wherein 0.10≤Y4≤0.14; Along the epitaxial direction, the Al composition content of the fourth N-polar well-followed gradient AlGaN layer decreases from X41 to X42, where 0.03 < X41 ≤ 0.15 and 0 ≤ X42 ≤ 0.

03.

8. The low operating current density blue Micro-LED epitaxial structure according to claim 7, characterized in that, The first, second, third, and fourth N-polar well-pre-graded InGaN layers are all doped with Si, with a Si doping concentration of 1.12 × 10⁻⁶. 17 / cm 3 ~6.75×10 17 / cm 3 The growth thickness was 0.1 nm to 0.8 nm. The first, second, third, and fourth N-polar InGaN quantum well layers are all made of undoped N-polar InGaN material, and their growth thicknesses are all 2.1 nm to 4.8 nm. The first, second, third, and fourth N-polar well-graded AlGaN layers are all grown without intentional doping, and their thicknesses are all 0.1 nm to 0.8 nm. The Ga polar GaN quantum barrier layers in the violet light multi-quantum well layer, the light blue light multi-quantum well layer, the blue light multi-quantum well layer, and the violet light final quantum well layer are all Ga polar GaN materials doped with Si, with a growth thickness of 6nm~13nm and a Si doping concentration of 2.15×10⁻⁶. 17 / cm 3 ~8.79×10 17 / cm 3 .

9. A method for fabricating a low-current-density blue Micro-LED epitaxial structure, characterized in that, The method for preparing the low operating current density blue Micro-LED epitaxial structure according to any one of claims 1-8 comprises the following steps: (1) Selecting a substrate; (2) A buffer layer is grown on the substrate; (3) Introduce a Si doping source to grow an N-type semiconductor layer on the buffer layer; (4) A low-temperature stress relief layer is grown on the N-type semiconductor layer; (5) A multi-quantum well light-emitting layer is grown on the low-temperature stress relief layer; (6) A P-type semiconductor layer is grown on the multi-quantum-well light-emitting layer; The multi-quantum-well emitting layer comprises a violet multi-quantum-well layer, a light blue multi-quantum-well layer, a blue multi-quantum-well layer, and a violet end-quantum-well layer stacked sequentially along the epitaxial direction; the In content of the blue multi-quantum-well layer is greater than that of the light blue multi-quantum-well layer, and the In content of both the violet multi-quantum-well layer and the violet end-quantum-well layer is less than that of the light blue multi-quantum-well layer; The violet multi-quantum well layer, the light blue multi-quantum well layer, the blue multi-quantum well layer, and the violet end-quantum well layer all include N-polar gradient InGaN layer before the well, N-polar InGaN quantum well layer, N-polar gradient AlGaN layer after the well, and Ga-polar GaN quantum barrier layer that are periodically and alternately grown along the epitaxial direction. The N-polar well-before gradient InGaN layer is an N-polar InGaN material with increasing In content along the epitaxial direction, and the N-polar well-before gradient AlGaN layer is an N-polar AlGaN material with decreasing Al content along the epitaxial direction. After the N-polar InGaN quantum well layers, which consist of the light blue multi-quantum well layer and the violet quantum well layer, are periodically deposited and grown alternately, annealing treatment is required on the surface of the epitaxial layer material.

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