A Micro-LED epitaxial structure with high hole injection efficiency and preparation method thereof

Abstract

The present invention discloses a high hole injection efficiency Micro-LED epitaxial structure and a preparation method thereof, and relates to the field of semiconductor technology. The Micro-LED epitaxial structure of the present invention includes a multi-quantum well light-emitting layer, a multi-stage P-type hole injection enhancement layer and a P-type semiconductor layer; the multi-stage P-type hole injection enhancement layer includes a first-stage hole injection enhancement layer, a second-stage hole injection enhancement layer and a third-stage hole injection enhancement layer; the first-stage hole injection enhancement layer includes a first AlGaN layer and a first InGaN layer; the second-stage hole injection enhancement layer includes a second AlGaN layer and a second InGaN layer, and the second InGaN layer is doped with Mg; the third-stage hole injection enhancement layer includes a third AlGaN layer, a third InGaN layer and a fourth InGaN layer, and the third InGaN layer and the fourth InGaN layer are doped with Mg respectively. The Micro-LED epitaxial structure with high hole injection efficiency of the present invention can significantly improve the hole injection efficiency of the P-type semiconductor layer and improve the matching degree of the electron hole concentration in the multi-quantum well light-emitting layer region, thereby improving the light efficiency of the Micro-LED chip at a low operating current density.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a Micro-LED epitaxial structure with high hole injection efficiency and a preparation method thereof. Background Art

[0002] With the booming development of emerging wearable and portable technologies, micron-sized LED chips (Micro LED) have received great attention and research from scientific research institutions and enterprises due to their application prospects in display, visible light communication, biomedicine and other fields. In addition, Micro LED display has excellent performance such as nanosecond (ns) level high-speed response performance, stable characteristics of inorganic materials, high light efficiency, high reliability, high color purity and contrast, and transparency. The combination of these characteristics is unattainable by liquid crystal display (LCD) and organic LED (OLED).

[0003] Although Micro LED has many excellent characteristics, it also faces challenges in manufacturing technology and material device physics. For example, the problem of the decrease in device peak EQE and the increase in corresponding current density as the chip size decreases has not been completely solved. The operating current density is between 0.01 and 0.5 A / cm 2 The efficiency of Micro LEDs in this range is still obviously insufficient. In fact, even conventional-sized chips for general lighting and backlight display applications have relatively low efficiency at this current density. The reason is that conventional-sized chips have an operating current density of 20A / cm2 in order to balance efficiency and cost factors. 2 Up to 40A / cm 2 The corresponding epitaxial structure design and material growth aim to improve the efficiency at high current density, with a peak EQE of 1-4 A / cm 2 The current density range is not concerned with the device efficiency at low current density. Under different current densities, the dominant reasons for the light-emitting mechanism of LED devices are different, and the corresponding epitaxial layer structure should also change. For example, in the Micro LED working range of 0.01~0.5A / cm 2 Under low current density, the carrier concentration in the quantum well is relatively low, the proportion of Auger recombination is small, and the corresponding quantum well recombination volume can be reduced, which means that the number of quantum wells can be reduced, the number of defects can be reduced, and the EQE of the device under low current density can be improved; at the same time, electron leakage has not occurred or the proportion is very low under low current density, and the electron blocking layer structure not only fails to block electrons, but will block the injection of holes, thereby reducing the quantum efficiency of the device.

[0004] The epitaxial structure design of traditional visible light LEDs is based on traditional application scenarios of large chips, high currents and high powers, while the display applications of Micro LEDs require small size, low current and low power. LEDs designed with traditional epitaxial structures are no longer able to meet the application requirements of Micro LEDs. Therefore, redesigning the epitaxial structure of Micro LEDs suitable for small size, low current and low power, and improving their electro-optical conversion efficiency, is an important challenge currently faced by both academia and industry. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a Micro-LED epitaxial structure with high hole injection efficiency and a preparation method thereof, which can significantly improve the hole injection efficiency of the P-type semiconductor layer and improve the matching degree of the electron hole concentration in the multi-quantum well light-emitting layer region, thereby improving the luminous efficiency of the Micro-LED chip at low operating current density.

[0006] In order to solve the above technical problems, the present invention provides a high hole injection efficiency Micro-LED epitaxial structure, comprising a multi-quantum well light-emitting layer, a multi-stage P-type hole injection enhancement layer and a P-type semiconductor layer stacked in sequence;

[0007] The multi-stage P-type hole injection enhancement layer includes a first-stage hole injection enhancement layer, a second-stage hole injection enhancement layer and a third-stage hole injection enhancement layer which are sequentially stacked and grown from bottom to top;

[0008] The first-stage hole injection enhancement layer includes a first AlGaN layer and a first InGaN layer that are periodically and alternately grown from bottom to top;

[0009] The second-stage hole injection enhancement layer comprises a second AlGaN layer and a second InGaN layer that are periodically and alternately grown from bottom to top, and the second InGaN layer is doped with Mg element;

[0010] The third-stage hole injection enhancement layer includes a third AlGaN layer, a third InGaN layer and a fourth InGaN layer which are periodically and alternately grown from bottom to top, and the third InGaN layer and the fourth InGaN layer are doped with Mg element respectively.

[0011] As an improvement of the above solution, the doping concentration of Mg element in the second InGaN layer is 1.2×10 18 atoms / cm 3 ~5.6×10 18 atoms / cm 3 ;

[0012] The doping concentration of Mg in the third InGaN layer is 2.5×10 18atoms / cm 3 ~7.8×10 18 atoms / cm 3 ;

[0013] The doping concentration of Mg in the fourth InGaN layer is 3.6×10 18 atoms / cm 3 ~2.5×10 19 atoms / cm 3 .

[0014] As an improvement of the above solution, the Al component in the first AlGaN layer is 0.4-0.8, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr;

[0015] The Al component of the second AlGaN layer is 0.3-0.7, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr;

[0016] The Al component in the third AlGaN layer is 0.2-0.6, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr.

[0017] As an improvement of the above solution, the Al composition in the first AlGaN layer>the Al composition in the second AlGaN layer>the Al composition in the third AlGaN layer.

[0018] As an improvement of the above solution, the In component of the first InGaN layer is 0.02-0.05, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr;

[0019] The In composition of the second InGaN layer is 0.05-0.1, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr;

[0020] The In component of the third InGaN layer is 0.03-0.08, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr;

[0021] The In composition of the fourth InGaN layer is 0.06-0.12, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr.

[0022] As an improvement of the above solution, the In composition in the first InGaN layer is less than the In composition in the third InGaN layer, less than the In composition in the second InGaN layer, and less than the In composition in the fourth InGaN layer.

[0023] As an improvement of the above solution, the number of cycles of the alternating growth of the first-stage hole injection enhancement layer is 2 to 5;

[0024] The number of cycles of the alternating growth of the second-stage hole injection enhancement layer is 3 to 6;

[0025] The number of cycles of the alternating growth of the third-order hole injection enhancement layer is 3-8.

[0026] As an improvement of the above solution, the high hole injection efficiency Micro-LED epitaxial structure further includes a substrate, a buffer layer, an N-type semiconductor layer and a low-temperature stress release layer;

[0027] The substrate, the buffer layer, the N-type semiconductor layer, the low-temperature stress release layer, the multi-quantum well light-emitting layer, the multi-stage P-type hole injection enhancement layer and the P-type semiconductor layer are arranged in sequence from bottom to top.

[0028] Accordingly, the present invention also provides a method for preparing a Micro-LED epitaxial structure with high hole injection efficiency, which is used to prepare the above-mentioned Micro-LED epitaxial structure with high hole injection efficiency, comprising the following steps:

[0029] A multi-stage P-type hole injection enhancement layer and a P-type semiconductor layer are sequentially grown on the multi-quantum well light-emitting layer;

[0030] Wherein, the multi-stage P-type hole injection enhancement layer comprises a first-stage hole injection enhancement layer, a second-stage hole injection enhancement layer and a third-stage hole injection enhancement layer which are sequentially stacked and grown from bottom to top;

[0031] The first-order hole injection enhancement layer includes a first AlGaN layer and a first InGaN layer that are periodically and alternately grown from bottom to top; the second-order hole injection enhancement layer includes a second AlGaN layer and a second InGaN layer that are periodically and alternately grown from bottom to top, and the second InGaN layer is doped with Mg element; the third-order hole injection enhancement layer includes a third AlGaN layer, a third InGaN layer and a fourth InGaN layer that are periodically and alternately grown from bottom to top, and the third InGaN layer and the fourth InGaN layer are doped with Mg element respectively.

[0032] As an improvement of the above scheme, in the process of periodically alternating the growth of the third-stage hole injection enhancement layer, after the third InGaN layer is deposited, the surface is etched with H2 gas, and after the fourth InGaN layer is deposited, a recrystallization annealing treatment is performed.

[0033] The implementation of the present invention has the following beneficial effects: the technical solution does not set an electron blocking layer on the multi-quantum well light-emitting layer in the Micro-LED epitaxial structure, but sets a multi-stage P-type hole injection enhancement layer, which can effectively eliminate the blocking effect of the electron blocking layer structure on hole injection, and the technical solution performs structural and process design on the multi-stage P-type hole injection enhancement layer. The material of the multi-stage P-type hole injection enhancement layer of the technical solution is a three-stage AlGaInN multilayer structure. The design of this structure can not only significantly improve the hole injection efficiency of the P-type semiconductor layer, but also improve the matching degree of the electron hole concentration in the multi-quantum well light-emitting layer region, which can improve the luminous efficiency of the Micro-LED chip at low operating current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of a Micro-LED epitaxial structure with high hole injection efficiency in Example 1 of the present invention;

[0035] Figure 2 1 is a schematic diagram of the structure of a multi-stage P-type hole injection enhancement layer in a high hole injection efficiency Micro-LED epitaxial structure according to Example 1 of the present invention;

[0036] Among them, 100-substrate, 200-buffer layer, 300-N-type semiconductor layer, 400-low-temperature stress release layer, 500-multi-quantum well light-emitting layer, 600-multi-stage P-type hole injection enhancement layer, 700-P-type semiconductor layer, 610-first-stage hole injection enhancement layer, 611-first AlGaN layer, 612-first InGaN layer, 620-second-stage hole injection enhancement layer, 621-second AlGaN layer, 622-second InGaN layer, 630-third-stage hole injection enhancement layer, 631-third AlGaN layer, 632-third InGaN layer, 633-fourth InGaN layer. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0038] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. Raw materials used without specifying the manufacturer are all conventional products that can be obtained through commercial purchase.

[0039] The technical solution of the present invention is further explained below in conjunction with specific implementation methods.

[0040] like Figure 1 and Figure 2 As shown, a high hole injection efficiency Micro-LED epitaxial structure includes a multi-quantum well light-emitting layer 500, a multi-stage P-type hole injection enhancement layer 600 and a P-type semiconductor layer 700 which are stacked in sequence;

[0041] The multi-stage P-type hole injection enhancement layer 600 includes a first-stage hole injection enhancement layer 610, a second-stage hole injection enhancement layer 620 and a third-stage hole injection enhancement layer 630 which are sequentially stacked and grown from bottom to top;

[0042] The first-stage hole injection enhancement layer 610 includes a first AlGaN layer 611 and a first InGaN layer 612 that are periodically and alternately grown from bottom to top;

[0043] The second-stage hole injection enhancement layer 620 includes a second AlGaN layer 621 and a second InGaN layer 622 that are periodically and alternately grown from bottom to top, and the second InGaN layer 622 is doped with Mg element;

[0044] The third-stage hole injection enhancement layer 630 includes a third AlGaN layer 631 , a third InGaN layer 632 , and a fourth InGaN layer 633 that are periodically and alternately grown from bottom to top, and the third InGaN layer 632 and the fourth InGaN layer 633 are doped with Mg element, respectively.

[0045] It is worth noting that the traditional LED epitaxial structure is basically provided with an electron blocking layer, and electron leakage has not occurred or the proportion is very low under the low working current density of Micro-LED. The electron blocking layer structure not only does not block the electrons, but blocks the injection of holes, reducing the quantum efficiency of the device. In the present technical solution, an electron blocking layer is not provided on the multi-quantum well light-emitting layer 500 in the Micro-LED epitaxial structure, but a multi-stage P-type hole injection enhancement layer 600 is provided, which can effectively eliminate the blocking effect of the electron blocking layer structure on hole injection, and the present technical solution performs structural and process design on the multi-stage P-type hole injection enhancement layer 600. The material of the multi-stage P-type hole injection enhancement layer 600 of the present technical solution is a three-stage AlGaInN multilayer structure. The design of this structure can significantly improve the hole injection efficiency of the P-type semiconductor layer 700 and improve the matching degree of the electron hole concentration in the multi-quantum well light-emitting layer 500 region, thereby improving the light efficiency of the Micro-LED chip under low working current density.

[0046] Further explanation: the epitaxial structure design of traditional visible light LEDs is based on traditional application scenarios of large chips, large currents, and high powers, while the display applications of Micro LEDs require small size, low current, and low power. LEDs designed with traditional epitaxial structures can no longer meet the application requirements of Micro LEDs. Therefore, redesigning the epitaxial structure of Micro LEDs suitable for small size, low current, and low power, and improving their electro-optical conversion efficiency, is an important challenge currently faced by both academia and industry. The high hole injection efficiency Micro-LED epitaxial structure of the present technical solution includes, from bottom to top, a multi-quantum well light-emitting layer 500, a multi-stage P-type hole injection enhancement layer 600, and a P-type semiconductor layer 700. A conventional electron blocking layer is not provided on the multi-quantum well light-emitting layer 500, but a multi-stage P-type hole injection enhancement layer 600 is provided; the material of the multi-stage P-type hole injection enhancement layer 600 is a three-stage AlGaInN multilayer structure, and the material of the first-stage hole injection enhancement layer 610 is a first AlGaN layer 611 and a first InGaN layer 612 supercrystal that are not intentionally doped. The second-order hole injection enhancement layer 620 is a superlattice material of a second AlGaN layer 621 and a second InGaN layer 622, wherein the second InGaN layer 622 material is doped with Mg element; the third-order hole injection enhancement layer 630 is a multi-order material of a third AlGaN layer 631, a third InGaN layer 632 and a fourth InGaN layer 633 that are periodically and alternately grown from bottom to top, wherein the third AlGaN layer 631 is not intentionally doped, and the third InGaN layer 632 and the fourth InGaN layer 633 materials are doped with Mg element. The wide-bandgap AlGaN material in the multi-stage P-type hole injection enhancement layer 600 of the present technical solution, namely, the first AlGaN layer 611, the second AlGaN layer 621 and the third AlGaN layer 631, mainly plays a role in reducing the carrier mobility, and can prevent electrons from being injected into the P-type semiconductor layer 700 to cause electron leakage; the low-bandgap InGaN material in the multi-stage P-type hole injection enhancement layer 600, namely, the first InGaN layer 612, the second InGaN layer 622, the third InGaN layer 632 and the fourth InGaN layer 640, can effectively reduce the carrier mobility of the P-type semiconductor layer 700, thereby preventing electrons from being injected into the P-type semiconductor layer 700 and causing electron leakage. The aN layer 633 can store some holes, and at the same time can also weaken the blocking effect on holes and enhance the hole injection efficiency in the P-type semiconductor layer 700. At the same time, the second InGaN layer 622, the third InGaN layer 632 and the fourth InGaN layer 633 are doped with Mg elements, which can provide some holes to the multi-quantum well light-emitting layer 500 to participate in light emission, further improve the hole injection efficiency and improve the matching degree of the electron-hole concentration in the multi-quantum well light-emitting layer 500, so as to improve the light efficiency of the Micro-LED chip at low operating current density.

[0047] Further explanation: the doping concentration of Mg in the second InGaN layer 622 is 1.2×10 18 / cm 3 ~5.6×10 18 / cm 3 , an exemplary value is 1.2×10 18 / cm 3 , 1.5×10 18 / cm 3 , 2.0×10 18 / cm 3 , 2.8×10 18 / cm 3 , 3.0×10 18 / cm 3 , 3.5×10 18 / cm 3 4.0×10 18 / cm 3 5.0×10 18 / cm 3 , 5.6×10 18 / cm 3 , but not limited to this;

[0048] The doping concentration of Mg in the third InGaN layer 632 is 2.5×10 18 / cm 3 ~7.8×10 18 / cm 3 , an exemplary value is 2.5×10 18 / cm 3 , 3.0×10 18 / cm 3 , 3.5×10 18 / cm 3 4.0×10 18 / cm 3 , 4.5×10 18 / cm 3 , 5.2×10 18 / cm 3 , 6.0×10 18 / cm 3 , 7.0×10 18 / cm 3 , 7.8×10 18 / cm 3 , but not limited to this;

[0049] The doping concentration of Mg in the fourth InGaN layer 633 is 3.6×10 18 / cm 3 ~2.5×10 19 / cm 3 , an exemplary value is 3.6×10 18 / cm 3 , 5.0×10 18 / cm 3 , 6.0×10 18 / cm 3 , 7.8×10 18 / cm 3 9.0×10 18 / cm 3 , 1.0×10 19 / cm 3 , 1.5×10 19 / cm 3 , 2.5×10 19 / cm 3 , but not limited to this.

[0050] Further explanation, the Al component in the first AlGaN layer 611 is 0.4-0.8, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr;

[0051] The Al composition of the second AlGaN layer 621 is 0.3-0.7, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr;

[0052] The Al component in the third AlGaN layer 631 is 0.2-0.6, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr.

[0053] Specifically, the Al component in the first AlGaN layer 611 is 0.4~0.8, and exemplary ones are 0.4, 0.5, 0.6, 0.7, and 0.8, but not limited thereto; the growth thickness of the first AlGaN layer 611 is 0.8nm~3.6nm, and exemplary ones are 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, and 3.6nm, but not limited thereto; the growth temperature of the first AlGaN layer 611 is 900℃~1050℃, and exemplary ones are 900℃, 950℃, 1000℃, and 1050℃, but not limited thereto; the growth pressure of the first AlGaN layer 611 is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited thereto.

[0054] The Al component in the second AlGaN layer 621 is 0.3~0.7, and exemplary ones are 0.3, 0.4, 0.5, 0.6, and 0.7, but not limited thereto; the growth thickness of the second AlGaN layer 621 is 0.8nm~3.6nm, and exemplary ones are 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, and 3.6nm, but not limited thereto; the growth temperature of the second AlGaN layer 621 is 900℃~1050℃, and exemplary ones are 900℃, 950℃, 1000℃, and 1050℃, but not limited thereto; the growth pressure of the second AlGaN layer 621 is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited thereto.

[0055] The Al component in the third AlGaN layer 631 is 0.2~0.6, and exemplary ones are 0.2, 0.3, 0.4, 0.5, and 0.6, but not limited thereto; the growth thickness of the third AlGaN layer 631 is 0.8nm~3.6nm, and exemplary ones are 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, and 3.6nm, but not limited thereto; the growth temperature of the third AlGaN layer 631 is 900℃~1050℃, and exemplary ones are 900℃, 950℃, 1000℃, and 1050℃, but not limited thereto; the growth pressure of the third AlGaN layer 631 is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited thereto.

[0056] Further explanation, the In composition of the first InGaN layer 612 is 0.02-0.05, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr;

[0057] The In composition of the second InGaN layer 622 is 0.05-0.1, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr;

[0058] The In component of the third InGaN layer 632 is 0.03-0.08, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr;

[0059] The In composition of the fourth InGaN layer 633 is 0.06-0.12, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr.

[0060] Specifically, the In component of the first InGaN layer 612 is 0.02-0.05, exemplarily 0.02, 0.03, 0.04, 0.05, but not limited thereto; the growth thickness of the first InGaN layer 612 is 0.8nm-3.6nm, exemplarily 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.6nm, but not limited thereto; the growth temperature of the first InGaN layer 612 is 850℃~1020℃, exemplified by 850℃, 880℃, 900℃, 920℃, 950℃, 1000℃, 1020℃ but not limited thereto; the growth pressure of the first InGaN layer 612 is 50torr~320torr, exemplified by 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, 320torr but not limited thereto.

[0061] The In composition of the second InGaN layer 622 is 0.05-0.1, and is exemplarily 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1, but not limited thereto; the growth thickness of the second InGaN layer 622 is 0.8nm-3.6nm, and is exemplarily 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, and 3.6nm, but not limited thereto; the growth temperature of the second InGaN layer 622 is The temperature is 850°C~1020°C, and exemplary ones are 850°C, 880°C, 900°C, 920°C, 950°C, 1000°C, and 1020°C, but not limited to these; the growth pressure of the second InGaN layer 622 is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited to these.

[0062] The In component of the third InGaN layer 632 is 0.03-0.08, and exemplary ones are 0.03, 0.04, 0.05, 0.06, 0.07, and 0.08, but not limited thereto; the growth thickness of the third InGaN layer 632 is 0.8nm-3.6nm, and exemplary ones are 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, and 3.6nm, but not limited thereto; the growth thickness of the third InGaN layer 632 is 0.8nm-3.6nm, and exemplary ones are 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, and 3.6nm, but not limited thereto; The temperature is 850℃~1020℃, exemplified by 850℃, 880℃, 900℃, 920℃, 950℃, 1000℃, 1020℃ but not limited thereto; the growth pressure of the third InGaN layer 632 is 50torr~320torr, exemplified by 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, 320torr but not limited thereto.

[0063] The In composition of the fourth InGaN layer 633 is 0.06-0.12, exemplarily 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, but not limited thereto; the growth thickness of the fourth InGaN layer 633 is 0.8nm-3.6nm, exemplarily 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.6nm, but not limited thereto; the thickness of the fourth InGaN layer 633 is 0.8nm-3.6nm, exemplarily 0.8nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.6nm, but not limited thereto; The growth temperature is 850°C~1020°C, and exemplary ones are 850°C, 880°C, 900°C, 920°C, 950°C, 1000°C, and 1020°C, but not limited to these; the growth pressure of the fourth InGaN layer 633 is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited to these.

[0064] To further illustrate, the Al composition in the first AlGaN layer 611 (set as X1)> the Al composition in the second AlGaN layer 621 (set as X2)> the Al composition in the third AlGaN layer 631 (set as X3), that is, the Al composition of each sub-layer material in the multi-stage P-type hole injection enhancement layer is X1>X2>X3.

[0065] Further explanation: the In component in the first InGaN layer 612 (set as Y1) is less than the In component in the third InGaN layer 632 (set as Y3) is less than the In component in the second InGaN layer 622 (set as Y2) is less than the In component in the fourth InGaN layer 633 (set as Y4). That is, in the In component of the InGaN material of the multi-stage P-type hole injection enhancement layer of the technical solution, the first InGaN layer 612 is less than the third InGaN layer 632, less than the second InGaN layer 622, and less than the fourth InGaN layer 633, that is, the In component Y1<Y3<Y2<Y4.

[0066] It is worth noting that Al atoms are relatively small in size and react with NH3 gas to generate Al-N with a wide energy band gap, which has the strongest blocking effect on electron holes. Similarly, In atoms are relatively large in size and react with NH3 gas to generate In-N with a small energy band gap, which has the weakest effect on electron holes. The main function of the AlGaN material in the multi-stage P-type hole injection enhancement layer of this technical solution is to block electrons from entering the P-type semiconductor layer to cause electron leakage, but it will inevitably also play a role in blocking hole injection into the active area. Therefore, it should be designed close to the multi-quantum well. It is a wide bandgap material to enhance the effect of blocking electrons. The semiconductor material with a small bandgap should be designed near the P-type semiconductor layer to weaken the effect of blocking hole injection. Therefore, the multi-stage P-type hole injection enhancement layer superlattice material of the technical solution is designed from bottom to top with a structure of decreasing Al component (i.e. X1>X2>X3) and increasing In component (i.e. Y1<Y2<Y4). At the same time, due to the relatively large size of In atoms, the higher the In component of InGaN materials, the more conducive it is to Mg doping and incorporation into the lattice. Increasing Mg doping can enhance the hole injection effect of P-type materials.

[0067] To further illustrate, the number of cycles of the alternating growth of the first-stage hole injection enhancement layer 610 is 2-5, exemplarily 2, 3, 4, and 5, but not limited thereto.

[0068] The number of cycles of the alternating growth of the second-stage hole injection enhancement layer 620 is 3-6, exemplarily 3, 4, 5, and 6, but not limited thereto.

[0069] The number of cycles of the alternating growth of the third-stage hole injection enhancement layer 630 is 3-8, exemplarily 3, 4, 5, 6, 7, and 8, but not limited thereto.

[0070] Further explanation, the high hole injection efficiency Micro-LED epitaxial structure also includes a substrate 100, a buffer layer 200, an N-type semiconductor layer 300 and a low-temperature stress release layer 400;

[0071] The substrate 100 , the buffer layer 200 , the N-type semiconductor layer 300 , the low-temperature stress release layer 400 , the multi-quantum well light-emitting layer 500 , the multi-stage P-type hole injection enhancement layer 600 and the P-type semiconductor layer 700 are sequentially arranged from bottom to top.

[0072] Preferably, the substrate 100 is a sapphire substrate, a silicon substrate or a SiC substrate, but is not limited thereto. More preferably, it is a sapphire substrate.

[0073] Preferably, the buffer layer 200 may be an AlN layer or an AlGaN layer, but is not limited thereto. More preferably, it is an AlN layer.

[0074] Preferably, the N-type semiconductor layer 300 is a Si-doped GaN layer, and its Si doping concentration is 5×10 18 cm -3 ~5×10 19 cm -3 , thickness is 1μm~3μm.

[0075] Preferably, the multi-quantum well light-emitting layer 500 is an InGaN-GaN type multi-quantum well structure or an InGaN-AlGaN type multi-quantum well structure, but is not limited thereto. Preferably, the multi-quantum well light-emitting layer 500 is a periodic structure, the number of periods of which is 3 to 15, and each period includes sequentially stacked InGaN quantum well layers and GaN quantum barrier layers, wherein the proportion of In component in the InGaN quantum well layer is 0.1 to 0.3, the thickness of which is 3 nm to 5 nm, and the thickness of the GaN quantum barrier layer is 8 nm to 15 nm.

[0076] Preferably, the P-type semiconductor layer 700 is a Mg-doped GaN layer, and the Mg doping concentration is 1×10 19 cm -3 ~1×10 21 cm -3 .

[0077] A method for preparing a Micro-LED epitaxial structure with high hole injection efficiency, which is used to prepare the above-mentioned Micro-LED epitaxial structure with high hole injection efficiency, comprises the following steps:

[0078] A multi-stage P-type hole injection enhancement layer 600 and a P-type semiconductor layer 700 are sequentially grown on the multi-quantum well light-emitting layer 500;

[0079] The multi-stage P-type hole injection enhancement layer 600 includes a first-stage hole injection enhancement layer 610, a second-stage hole injection enhancement layer 620 and a third-stage hole injection enhancement layer 630 which are stacked and grown sequentially from bottom to top;

[0080] The first-order hole injection enhancement layer 610 includes a first AlGaN layer 611 and a first InGaN layer 612 that are periodically and alternately grown from bottom to top; the second-order hole injection enhancement layer 620 includes a second AlGaN layer 621 and a second InGaN layer 622 that are periodically and alternately grown from bottom to top, and the second InGaN layer 622 is doped with Mg element; the third-order hole injection enhancement layer 630 includes a third AlGaN layer 631, a third InGaN layer 632 and a fourth InGaN layer 633 that are periodically and alternately grown from bottom to top, and the third InGaN layer 632 and the fourth InGaN layer 633 are doped with Mg element respectively.

[0081] The present technical solution does not set an electron blocking layer on the multi-quantum well light-emitting layer 500 but sets a multi-stage P-type hole injection enhancement layer 600, which can eliminate the blocking effect of the conventional electron blocking layer structure on hole injection. At the same time, the Micro-LED chip prepared by the present technical solution can significantly improve the hole injection efficiency of the P-type semiconductor layer 700, and improve the matching degree of the electron hole concentration in the multi-quantum well light-emitting layer 500 region, thereby improving the luminous efficiency of the Micro-LED chip at low operating current density.

[0082] Specifically, in one embodiment of the present invention, the high hole injection efficiency Micro-LED epitaxial structure also includes a substrate 100, a buffer layer 200, an N-type semiconductor layer 300 and a low-temperature stress release layer 400; the substrate 100, the buffer layer 200, the N-type semiconductor layer 300, the low-temperature stress release layer 400, the multi-quantum well light-emitting layer 500, the multi-stage P-type hole injection enhancement layer 600 and the P-type semiconductor layer 700 are arranged in sequence from bottom to top. The preparation method of the above Micro-LED epitaxial structure includes the following steps:

[0083] (1) Selecting a substrate 100;

[0084] (2) growing a buffer layer 200 on the substrate 100;

[0085] (3) introducing a Si doping source to grow an N-type semiconductor layer 300 on the buffer layer 200;

[0086] (4) growing a low-temperature stress release layer 400 on the N-type semiconductor layer 300;

[0087] (5) growing a multi-quantum well light-emitting layer 500 on the low-temperature stress release layer 400;

[0088] (6) growing a multi-stage P-type hole injection enhancement layer 600 on the multi-quantum well light-emitting layer 500;

[0089] (7) A P-type semiconductor layer 700 is grown on the multi-stage P-type hole injection enhancement layer 600 to obtain a Micro-LED epitaxial structure with high hole injection efficiency.

[0090] To further illustrate, during the periodic alternating growth of the third-stage hole injection enhancement layer 630, after the third InGaN layer 632 is deposited, a surface H2 gas etching treatment is performed, and after the fourth InGaN layer 633 is deposited, a recrystallization annealing treatment is performed.

[0091] It is worth noting that in the process of periodically alternating the growth of the third-order hole injection enhancement layer 630, the third InGaN layer 632 needs to be etched with H2 gas on the surface after the deposition is completed, and the fourth InGaN layer 633 needs to be annealed after the deposition is completed. The material with poor crystalline quality on the surface of the third InGaN layer 632 after the surface H2 gas etching treatment will be decomposed, and the material with poor crystalline quality on the surface of the fourth InGaN layer 633 after the recrystallization annealing treatment will be decomposed, and then react with NH3 in the reaction chamber to recrystallize and deposit on the surface of the fourth InGaN layer 633 material, which is beneficial to improving the quality of the epitaxial material, and the material with poor crystalline quality on the surface of the third InGaN layer 632 after the surface H2 gas etching treatment will be decomposed to form a relatively rough surface, which can effectively reduce the in-plane total reflection of the semiconductor material, which is beneficial to the photon escape from the material in the active area, and the rough surface can release part of the stress of the epitaxial layer material, improve the quality of the epitaxial layer material, and further improve the light efficiency of the Micro-LED chip at a low operating current density.

[0092] Specifically, in some embodiments, after the deposition of the third InGaN layer 632 is completed, the method for performing surface H2 gas etching treatment includes the following steps: after the deposition and growth of the third InGaN layer 632 is completed, H2 / N2 mixed gas is intermittently and cyclically introduced into the reaction chamber and stabilized for 3 to 25 seconds. The material with poor crystallization quality on the surface of the third InGaN layer 632 that has been subjected to the surface H2 gas etching treatment will be decomposed, which is beneficial to improving the crystal quality of the material. The temperature of the surface H2 gas etching treatment is 880°C to 1050°C, and the pressure is 50 torr to 320 torr.

[0093] Specifically, the temperature of the surface H2 gas etching treatment is 880℃~1050℃, and exemplary ones are 880℃, 900℃, 920℃, 950℃, 1000℃, and 1050℃, but not limited to these; the pressure of the surface H2 gas etching treatment is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited to these.

[0094] Preferably, the volume ratio of H2 to N2 in the H2 / N2 mixed gas is 1:0.1 to 10. Exemplary are 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.8, 1:1, 1:2, 1:5, 1:10, but not limited thereto. In a preferred embodiment of the present technical solution, the volume ratio of H2 to N2 in the H2 / N2 mixed gas is 1:0.1.

[0095] Specifically, in some embodiments, after the deposition of the fourth InGaN layer 633 is completed, a recrystallization annealing method includes the following steps: after the deposition and growth of the fourth InGaN layer 633 is completed, a H2 / NH3 / N2 mixed gas needs to be intermittently and cyclically introduced into the reaction chamber and stabilized for 5 to 36 seconds. After the recrystallization annealing treatment, the material with poor crystallization quality on the surface of the fourth InGaN layer 633 will be decomposed, and then react with the NH3 in the reaction chamber to recrystallize and deposit on the surface of the fourth InGaN layer 633 material, which is beneficial to improving the quality of the epitaxial material. The temperature of the recrystallization annealing treatment is 880°C to 1050°C, and the pressure is 50 torr to 320 torr.

[0096] Specifically, the temperature of the recrystallization annealing treatment is 880°C~1050°C, and exemplary ones are 880°C, 900°C, 920°C, 950°C, 1000°C, and 1050°C, but not limited to these; the pressure of the recrystallization annealing treatment is 50torr~320torr, and exemplary ones are 50torr, 100torr, 150torr, 200torr, 220torr, 300torr, and 320torr, but not limited to these.

[0097] Preferably, the volume ratio of H2, NH3 and N2 in the H2 / NH3 / N2 mixed gas is 1:(0.25-5):(0.1-10). In a preferred embodiment of the present technical solution, the volume ratio of H2, NH3 and N2 in the H2 / NH3 / N2 mixed gas is 1:0.5:4.

[0098] The technical solution of the present invention is further described below through examples and comparative examples.

[0099] Example 1

[0100] The high hole injection efficiency Micro-LED epitaxial structure of this embodiment includes, from bottom to top, a substrate 100, a buffer layer 200, an N-type semiconductor layer 300, a low-temperature stress release layer 400, a multi-quantum well light-emitting layer 500, a multi-stage P-type hole injection enhancement layer 600 and a P-type semiconductor layer 700;

[0101] The multi-stage P-type hole injection enhancement layer 600 includes a first-stage hole injection enhancement layer 610, a second-stage hole injection enhancement layer 620 and a third-stage hole injection enhancement layer 630 which are sequentially stacked and grown from bottom to top;

[0102] The first-stage hole injection enhancement layer 610 includes a first AlGaN layer 611 and a first InGaN layer 612 that are periodically and alternately grown from bottom to top;

[0103] The second-stage hole injection enhancement layer 620 includes a second AlGaN layer 621 and a second InGaN layer 622 that are periodically and alternately grown from bottom to top, and the second InGaN layer 622 is doped with Mg element;

[0104] The third-stage hole injection enhancement layer 630 includes a third AlGaN layer 631 , a third InGaN layer 632 and a fourth InGaN layer 633 which are periodically and alternately grown from bottom to top, and the third InGaN layer 632 and the fourth InGaN layer 633 are doped with Mg element respectively.

[0105] The first-order hole injection enhancement layer 610 alternately grows in a period range of 3; the first AlGaN layer 611 is not intentionally doped, the Al component in the first AlGaN layer 611 is 0.6, the growth thickness is 2.5 nm, the growth temperature is 950° C., and the pressure is 220 torr; the first InGaN layer 612 is not intentionally doped, the In component is 0.03, the thickness is 2.5 nm, the growth temperature is 920° C., and the pressure is 220 torr;

[0106] The second-order hole injection enhancement layer 620 has an alternating growth period of 4; the second AlGaN layer 621 is not intentionally doped, the Al component is 0.5, the growth thickness is 2.5nm, the growth temperature is 950℃, and the pressure is 220torr; the second InGaN layer 622 is doped with Mg, the In component is 0.07, the thickness is 2.5nm, and the Mg doping concentration is 2.8×10 18 / cm³, growth temperature is 920℃, pressure is 220torr;

[0107] The third-order hole injection enhancement layer 630 has an alternating growth period of 6; the third AlGaN layer 631 is not intentionally doped, the Al component is 0.4, the growth thickness is 2.5nm, the growth temperature is 950℃, and the pressure is 220torr; the third InGaN layer 632 is doped with Mg element, the In component is 0.05, the thickness is 2.5nm, and the Mg doping concentration is 5.2×10 18 / cm³, the growth temperature is 920℃, and the pressure is 220torr; the fourth InGaN layer 633 material is doped with Mg element, the In component is 0.09, the thickness is 2.5nm, and the Mg doping concentration is 7.8×10 18 / cm³, growth temperature is 920℃, pressure is 220torr;

[0108] In this embodiment, the Al composition in the first AlGaN layer 611 (X1=0.6)>the Al composition in the second AlGaN layer 621 (X2=0.5)>the Al composition in the third AlGaN layer 631 (X3=0.4); the In composition in the first InGaN layer 612 (Y1=0.03)<the In composition in the third InGaN layer 632 (Y3=0.05)<the In composition in the second InGaN layer 622 (Y2=0.07)<the In composition in the fourth InGaN layer 633 (Y4=0.09).

[0109] The method for preparing a Micro-LED epitaxial structure with high hole injection efficiency in this embodiment includes the following steps:

[0110] (1) Selecting a substrate 100;

[0111] (2) growing a buffer layer 200 on the substrate 100;

[0112] (3) introducing a Si doping source to grow an N-type semiconductor layer 300 on the buffer layer 200;

[0113] (4) growing a low-temperature stress release layer 400 on the N-type semiconductor layer 300;

[0114] (5) growing a multi-quantum well light-emitting layer 500 on the low-temperature stress release layer 400;

[0115] (6) growing a multi-stage P-type hole injection enhancement layer 600 on the multi-quantum well light-emitting layer 500;

[0116] (7) growing a P-type semiconductor layer 700 on the multi-level P-type hole injection enhancement layer 600;

[0117] Among them, in step (6) of growing a multi-stage P-type hole injection enhancement layer 600 on the multi-quantum well light-emitting layer 500, after the deposition of the third InGaN layer 632 is completed during the periodic alternating growth of the third-stage hole injection enhancement layer 630, a surface H2 gas etching treatment is required. That is, after the deposition and growth of the third InGaN layer 632 is completed, it is necessary to intermittently and cyclically introduce H2 / N2 mixed gas into the reaction chamber and stabilize it for 15 seconds. After the surface H2 gas etching treatment, the material with poor crystalline quality on the surface of the third InGaN layer 632 will be decomposed, which is beneficial to improving the crystal quality of the material. Among them, the temperature of the surface H2 gas etching treatment is 920°C and the pressure is 220torr.

[0118] After the deposition of the fourth InGaN layer 633 is completed, a recrystallization annealing treatment is required. That is, after the deposition and growth of the fourth InGaN layer 633 is completed, a H2 / NH3 / N2 mixed gas needs to be intermittently and cyclically introduced into the reaction chamber and stabilized for 15 seconds. After the recrystallization annealing treatment, the material with poor crystallization quality on the surface of the fourth InGaN layer 633 will be decomposed, and then react with the NH3 in the reaction chamber to recrystallize and deposit on the surface of the fourth InGaN layer 633 material, which is beneficial to improving the quality of the epitaxial material. The temperature of the recrystallization annealing treatment is 950°C and the pressure is 220torr.

[0119] Example 2

[0120] This embodiment provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Embodiment 1, except that:

[0121] The Al component of the first AlGaN layer 611 is 0.8, the growth thickness is 2.0 nm, the growth temperature is 900° C., and the pressure is 150 torr; the In component of the first InGaN layer 612 is 0.02, the thickness is 2.0 nm, the growth temperature is 850° C., and the pressure is 150 torr;

[0122] The second AlGaN layer 621 is grown with a thickness of 2.0 nm, a growth temperature of 900°C, and a pressure of 150 torr; the second InGaN layer 622 is grown with a thickness of 2.0 nm, and a Mg doping concentration of 3.5×10 18 / cm³, the growth temperature is 900℃ and the pressure is 150torr.

[0123] Example 3

[0124] This embodiment provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Embodiment 1, except that:

[0125] The period range of the alternating growth of the third-order hole injection enhancement layer 630 is 8, the Al component of the third AlGaN layer 631 is 0.2; the In component of the third InGaN layer 632 is 0.06, and the Mg doping concentration is 7.8×10 18 / cm 3 .

[0126] Example 4

[0127] This embodiment provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Embodiment 1, except that:

[0128] The In composition (Y1) of the first InGaN layer 612 is 0.05, the In composition (Y2) of the second InGaN layer 622 is 0.09, the In composition (Y3) of the third InGaN layer 632 is 0.07, the In composition of the fourth InGaN layer 633 is 0.12, the thickness is 1.5 nm, and the Mg doping concentration is 1.5×10 19 / cm³, growth temperature is 1020℃, pressure is 220torr;

[0129] That is, in this embodiment, the In composition in the first InGaN layer 612 (Y1=0.05)<In composition in the third InGaN layer 632 (Y3=0.07)<In composition in the second InGaN layer 622 (Y2=0.09)<In composition in the fourth InGaN layer 633 (Y4=0.12).

[0130] Comparative Example 1——(with an electron blocking layer but without a multi-stage P-type hole injection enhancement layer)

[0131] The present comparative example provides a Micro-LED epitaxial structure, which includes, from bottom to top, a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress release layer, a multi-quantum well light-emitting layer, a multi-order P-type electron blocking layer, and a P-type semiconductor layer; wherein the multi-order P-type electron blocking layer includes a first-order electron blocking layer, a second-order electron blocking layer, a third-order electron blocking layer, and a fourth-order electron blocking layer sequentially stacked on the multi-quantum well light-emitting layer;

[0132] The first-order electron blocking layer is a superlattice structure composed of alternately stacked AlN layers and GaN layers, grown at a growth temperature of 950°C and a growth pressure of 100 torr. The thickness of the AlN layer is 4nm, the thickness of the GaN layer is 3nm, the number of periods is 3, and the total thickness is 21nm.

[0133] The second-order electron blocking layer is a superlattice structure composed of an alternately stacked first AlGaN layer and a first Mg-doped GaN layer. In the first AlGaN layer, the Al component is 0.4, and the Mg doping concentration in the first Mg-doped GaN layer is 3×10 18 / cm 3 The growth temperature is 950°C and the growth pressure is 100 torr. The thickness of the first AlGaN layer is 2nm, the thickness of the first Mg-doped GaN layer is 3nm, the number of periods is 4, and the total thickness is 20nm.

[0134] The third-order electron blocking layer is a superlattice structure composed of an alternately stacked second AlGaN layer and a first Mg-doped InGaN layer. In the second AlGaN layer, the Al component is 0.2, in the first Mg-doped InGaN layer, the In component is 0.03, and the Mg doping concentration is 8×10 18 / cm 3 Grown at a growth temperature of 950°C and a growth pressure of 100 torr, the thickness of the second AlGaN layer is 3nm, the thickness of the first Mg-doped InGaN layer is 3nm, the number of periods is 5, and the total thickness is 30nm.

[0135] The fourth-order electron blocking layer is a superlattice structure composed of an alternately stacked second Mg-doped GaN layer and a second Mg-doped InGaN layer. The Mg doping concentration in the second Mg-doped GaN layer is 1.2×10 19 / cm 3 In the second Mg-doped InGaN layer, the In composition is 0.09 and the Mg doping concentration is 1.2×10 19 / cm 3 Under the conditions of growth temperature of 950°C and growth pressure of 100 torr, the thickness of the second Mg-doped GaN layer is 2nm, the thickness of the second Mg-doped InGaN layer is 2nm, the number of periods is 7, and the total thickness is 28nm.

[0136] Comparative Example 2

[0137] This comparative example provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Example 1, except that:

[0138] In the present comparative example, when preparing the Micro-LED epitaxial structure, during the periodic alternating growth of the third-stage hole injection enhancement layer 630, after the deposition of the third InGaN layer 632, no surface H2 gas etching treatment is performed, and at the same time, after the deposition of the fourth InGaN layer 633, no recrystallization annealing treatment is performed.

[0139] Comparative Example 3

[0140] This comparative example provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Example 1, except that:

[0141] In this comparative example, the fourth InGaN layer 633 is not doped with Mg.

[0142] Comparative Example 4

[0143] This comparative example provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Example 1, except that:

[0144] In this comparative example, the Al composition (X1) in the first AlGaN layer 611 is 0.4, the Al composition (X2) in the second AlGaN layer 621 is 0.6, and the Al composition (X3) in the third AlGaN layer 631 is 0.8, that is, in this comparative example, the Al composition (X1) in the first AlGaN layer 611 is less than the Al composition (X2) in the second AlGaN layer 621 and less than the Al composition (X3) in the third AlGaN layer 631.

[0145] Comparative Example 5

[0146] This comparative example provides a high hole injection efficiency Micro-LED epitaxial structure, which is basically the same as Example 1, except that:

[0147] In this comparative example, the In component (Y1) in the first InGaN layer 612 is 0.12, the In component (Y2) in the second InGaN layer 622 is 0.1, the In component (Y3) in the third InGaN layer 632 is 0.08, and the In component (Y4) in the fourth InGaN layer 633 is 0.06, that is, in this comparative example, the In component (Y1) in the first InGaN layer 612>the In component (Y2) in the second InGaN layer 622>the In component (Y3) in the third InGaN layer 632>the In component (Y4) in the fourth InGaN layer 633.

[0148] Performance Testing:

[0149] The Micro-LED epitaxial structures obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were prepared into 20 μm×20 μm Micro-LED chips using the same chip process conditions, and their luminous efficiency was tested at a working current of 0.5 μA. Based on Comparative Example 1, the luminous efficiency improvement rate in each Example and Comparative Example was calculated:

[0150] Light efficiency improvement rate = (improved light efficiency - original light efficiency) / original light efficiency × 100%;

[0151] In the above calculation formula: the original light effect is the light effect of comparative example 1.

[0152] Specifically, the test results are shown in Table 1 below:

[0153] Table 1 Performance test results

[0154]

[0155] It can be seen from the above experimental data that the present technical solution does not set an electron blocking layer on the multi-quantum well light-emitting layer but sets a multi-stage P-type hole injection enhancement layer, and designs the structure and process of the multi-stage P-type hole injection enhancement layer, that is, the material of the multi-stage P-type hole injection enhancement layer is a three-stage AlGaInN multilayer structure. The design of this structure can significantly improve the hole injection efficiency of the P-type semiconductor layer and improve the matching degree of the electron hole concentration in the multi-quantum well light-emitting layer region, thereby improving the luminous efficiency of the prepared Micro-LED chip at low operating current density.

[0156] The above disclosure is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A Micro-LED epitaxial structure with high hole injection efficiency, characterized in that: It includes a multi-quantum well light-emitting layer, a multi-stage P-type hole injection enhancement layer and a P-type semiconductor layer which are stacked in sequence; The multi-stage P-type hole injection enhancement layer includes a first-stage hole injection enhancement layer, a second-stage hole injection enhancement layer and a third-stage hole injection enhancement layer which are sequentially stacked and grown from bottom to top; The first-stage hole injection enhancement layer includes a first AlGaN layer and a first InGaN layer that are periodically and alternately grown from bottom to top; The second-stage hole injection enhancement layer comprises a second AlGaN layer and a second InGaN layer that are periodically and alternately grown from bottom to top, and the second InGaN layer is doped with Mg element; The third-stage hole injection enhancement layer includes a third AlGaN layer, a third InGaN layer and a fourth InGaN layer which are periodically and alternately grown from bottom to top, and the third InGaN layer and the fourth InGaN layer are both doped with Mg element.

2. The high hole injection efficiency Micro-LED epitaxial structure according to claim 1, characterized in that: The doping concentration of Mg in the second InGaN layer is 1.2×10 18 ~5.6×10 18 atoms / cm 3 ; The doping concentration of Mg in the third InGaN layer is 2.5×10 18 ~7.8×10 18 atoms / cm 3 ; The doping concentration of Mg in the fourth InGaN layer is 3.6×10 18 ~2.5×10 19 atoms / cm 3 .

3. The high hole injection efficiency Micro-LED epitaxial structure according to claim 1, characterized in that: The Al component of the first AlGaN layer is 0.4-0.8, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr; The Al component of the second AlGaN layer is 0.3-0.7, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr; The Al component in the third AlGaN layer is 0.2-0.6, the growth thickness is 0.8nm-3.6nm, the growth temperature is 900°C-1050°C, and the pressure is 50torr-320torr.

4. The high hole injection efficiency Micro-LED epitaxial structure according to claim 3, characterized in that: The Al composition in the first AlGaN layer>the Al composition in the second AlGaN layer>the Al composition in the third AlGaN layer.

5. The high hole injection efficiency Micro-LED epitaxial structure according to claim 1, characterized in that: The In component of the first InGaN layer is 0.02-0.05, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr; The In composition of the second InGaN layer is 0.05-0.1, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr; The In component of the third InGaN layer is 0.03-0.08, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr; The In composition of the fourth InGaN layer is 0.06-0.12, the growth thickness is 0.8nm-3.6nm, the growth temperature is 850°C-1020°C, and the pressure is 50torr-320torr.

6. The high hole injection efficiency Micro-LED epitaxial structure according to claim 5, characterized in that: The In composition in the first InGaN layer is less than the In composition in the third InGaN layer, less than the In composition in the second InGaN layer, and less than the In composition in the fourth InGaN layer.

7. The high hole injection efficiency Micro-LED epitaxial structure according to claim 1, characterized in that: The number of cycles of the alternating growth of the first-stage hole injection enhancement layer is 2 to 5; The number of cycles of the alternating growth of the second-stage hole injection enhancement layer is 3 to 6; The number of cycles of the alternating growth of the third-order hole injection enhancement layer is 3-8.

8. The high hole injection efficiency Micro-LED epitaxial structure according to claim 1, characterized in that: The high hole injection efficiency Micro-LED epitaxial structure also includes a substrate, a buffer layer, an N-type semiconductor layer and a low-temperature stress release layer; The substrate, the buffer layer, the N-type semiconductor layer, the low-temperature stress release layer, the multi-quantum well light-emitting layer, the multi-stage P-type hole injection enhancement layer and the P-type semiconductor layer are arranged in sequence from bottom to top.

9. A method for preparing a Micro-LED epitaxial structure with high hole injection efficiency, characterized in that: The method for preparing the high hole injection efficiency Micro-LED epitaxial structure according to any one of claims 1 to 8 comprises the following steps: A multi-stage P-type hole injection enhancement layer and a P-type semiconductor layer are sequentially grown on the multi-quantum well light-emitting layer; Wherein, the multi-stage P-type hole injection enhancement layer comprises a first-stage hole injection enhancement layer, a second-stage hole injection enhancement layer and a third-stage hole injection enhancement layer which are sequentially stacked and grown from bottom to top; The first-order hole injection enhancement layer includes a first AlGaN layer and a first InGaN layer that are periodically and alternately grown from bottom to top; the second-order hole injection enhancement layer includes a second AlGaN layer and a second InGaN layer that are periodically and alternately grown from bottom to top, and the second InGaN layer is doped with Mg element; the third-order hole injection enhancement layer includes a third AlGaN layer, a third InGaN layer and a fourth InGaN layer that are periodically and alternately grown from bottom to top, and the third InGaN layer and the fourth InGaN layer are both doped with Mg element.

10. The method for preparing a Micro-LED epitaxial structure with high hole injection efficiency according to claim 9, characterized in that: In the process of periodically alternating the growth of the third-stage hole injection enhancement layer, after the deposition of the third InGaN layer is completed, a surface H2 gas etching treatment is performed, and after the deposition of the fourth InGaN layer is completed, a recrystallization annealing treatment is performed.

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