An epitaxial structure of a blue Micro-LED and its fabrication method

Abstract

The present invention relates to the technical field of semiconductor materials, and discloses an epitaxial structure of a blue light Micro-LED and a preparation method thereof, wherein the epitaxial structure comprises a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress release layer, a multi-quantum well light-emitting layer, an electron blocking layer and a P-type semiconductor layer stacked sequentially on the substrate, wherein the multi-quantum well light-emitting layer comprises a first light blue light multi-quantum well sublayer, a second light blue light multi-quantum well sublayer, a third blue light multi-quantum well sublayer and a fourth light blue light multi-quantum well sublayer stacked sequentially from bottom to top, wherein each sublayer is a superlattice structure of an InGaN multi-quantum well layer and a multi-quantum barrier layer. The implementation of the present invention can reduce the stress during the growth of the InGaN quantum well, significantly improve the quality of the multi-quantum well light-emitting layer, and at the same time improve the hole injection efficiency of the P-type semiconductor layer, thereby improving the light efficiency, yield and other performances of the Micro-LED chip at a low operating current density, and is suitable for small-size, low-current and low-power blue light Micro-LED.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and in particular to an epitaxial structure of a blue light Micro-LED 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 and biomedicine. Micro-LED display has excellent performance such as nanosecond (ns) level high-speed response, 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 properties, it also faces challenges in manufacturing technology and material device physics. For example, the problem of the decrease in device peak external quantum efficiency (EQE) and the corresponding increase in current density as the chip size decreases has not been completely solved. The operating current density is 0.01A / cm 2 ~0.5A / cm 2 The efficiency of Micro-LEDs in this range is still significantly low. 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 ~40A / cm 2 The corresponding epitaxial structure design and material growth also aim to improve efficiency at high current density, with a peak EQE of 1A / cm2. 2 ~4A / cm² current density range, without paying attention to the device efficiency at low current density.

[0004] At 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 0.01A / cm2 range of Micro-LED working range, 2 ~0.5A / cm 2At 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 can reduce the number of quantum wells, reduce the number of defects, and improve the EQE of the device at low current density; at the same time, electron leakage has not occurred or the proportion is very low at low current density. The electron blocking layer structure not only has no effect of blocking electrons, but will block the injection of holes, reducing the quantum efficiency of the device. Therefore, in-depth mechanism research, design and growth of LED epitaxial layer structure under low current density working conditions of Micro-LED is a necessary key technology for the development of high-efficiency Micro-LED devices driven by low working current density.

[0005] The epitaxial structure design of traditional visible light LEDs is based on traditional application scenarios of large chips, high currents, and high powers. However, the display applications of Micro-LEDs require small size, low current density, 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 density, 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

[0006] The technical problem to be solved by the present invention is to provide an epitaxial structure of a blue light Micro-LED and a preparation method thereof, which can reduce the stress during the growth of InGaN quantum wells, improve the crystal quality of the multi-quantum well layer, and thus improve the internal quantum efficiency of the Micro-LED.

[0007] In order to solve the above technical problems, the first aspect of the present invention provides an epitaxial structure of a blue light Micro-LED, comprising a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress release layer, a multi-quantum well light-emitting layer, an electron blocking layer and a P-type semiconductor layer sequentially stacked on the substrate;

[0008] The multi-quantum well light-emitting layer comprises a first light blue multi-quantum well sublayer, a second light blue multi-quantum well sublayer, a third blue multi-quantum well sublayer and a fourth light blue multi-quantum well sublayer, which are sequentially stacked from bottom to top;

[0009] The first light blue multi-quantum well sublayer is a superlattice structure of a first InGaN multi-quantum well layer and a first multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2 to 6;

[0010] The second light blue multi-quantum well sublayer is a superlattice structure of a second InGaN multi-quantum well layer and a second multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top, with a period number of 1 to 5;

[0011] The third blue light multi-quantum well sublayer is a superlattice structure of a third InGaN multi-quantum well layer and a third Si-doped GaN multi-quantum barrier layer that are periodically and alternately grown from bottom to top; the number of periods is 2 to 8;

[0012] The fourth light blue multi-quantum well sublayer is a superlattice structure of a fourth InGaN multi-quantum well layer and a fourth multi-quantum barrier layer that are periodically and alternately grown from bottom to top, with the number of periods being 2.

[0013] As an improvement of the above solution, the first InGaN multi-quantum well layer is a non-doped single-layer structure or a multi-layer structure, and the In component is x1, 0.08≤x1≤0.15; the thickness of the first InGaN multi-quantum well layer is 2.2nm~3.8nm;

[0014] The second InGaN multi-quantum well layer is a non-doped single-layer structure or a multi-layer structure, and the In component ratio is x2, 0.1≤x2≤0.18; the thickness of the second InGaN multi-quantum well layer is 2.2nm~3.8nm;

[0015] The third InGaN multi-quantum well layer is a non-doped single-layer structure or a multi-layer structure, and the In component ratio is x3, 0.13≤x3≤0.21; the thickness of the third InGaN multi-quantum well layer is 2.5nm~4.2nm;

[0016] The fourth InGaN multi-quantum well layer is a non-doped InGaN multi-quantum well layer and / or a Mg-doped InGaN multi-quantum well layer, and the In component is x4, 0.08≤x4≤0.18; the thickness of the fourth InGaN multi-quantum well layer is 2.2nm~3.8nm.

[0017] As an improvement of the above solution, the first multi-quantum well composite barrier layer includes a first Si-doped GaN barrier layer, a first AlGaN barrier layer and a first GaN barrier layer which are sequentially stacked and grown from bottom to top;

[0018] The thickness of the first Si-doped GaN barrier layer is 1 nm to 8 nm, and the Si doping concentration is 1.2×10 17 / cm 3 ~7.6×10 18 / cm 3 ; The Al component in the first AlGaN barrier layer is y1, 0.02≤y1≤0.36; The thickness of the first AlGaN barrier layer is 0.5nm~6.6nm; The thickness of the first GaN barrier layer is 1nm~8nm;

[0019] The second multi-quantum well composite barrier layer includes a second Si-doped GaN barrier layer, a second AlGaN barrier layer and a second GaN barrier layer which are sequentially stacked and grown from bottom to top;

[0020] The thickness of the second Si-doped GaN barrier layer is 1 nm to 8 nm, and the Si doping concentration is 1.2×10 17 / cm 3 ~7.6×10 18 / cm 3 ;

[0021] The Al component in the second AlGaN barrier layer is y2, 0.02≤y2≤0.36; the thickness of the second AlGaN barrier layer is 0.5nm~6.6nm;

[0022] The thickness of the second GaN barrier layer is 1 nm to 8 nm.

[0023] As an improvement of the above solution, the total thickness of the first multi-quantum well composite barrier layer is 7nm~16nm;

[0024] The total thickness of the second multi-quantum well composite barrier layer is 7nm-16nm;

[0025] The thickness ratio of the first InGaN multi-quantum well layer to the first multi-quantum well composite barrier layer is 1:(2.5-5);

[0026] The thickness ratio of the second InGaN multi-quantum well layer to the second multi-quantum well composite barrier layer is 1:(2.5-5).

[0027] As an improvement of the above solution, the third Si-doped GaN multi-quantum barrier layer is a single-layer structure or a multi-layer structure doped with Si element, and the doping concentration of Si is 1.2×10 17 / cm 3 ~8.6×10 17 / cm 3 ;

[0028] The thickness of the third Si-doped GaN multi-quantum barrier layer is 6.5 nm to 13.6 nm.

[0029] As an improvement of the above scheme, the thickness ratio of the third InGaN multi-quantum well layer to the third Si-doped GaN multi-quantum barrier layer is 1:(2.4-4.5);

[0030] The thickness ratio of the fourth InGaN multi-quantum well layer to the fourth multi-quantum barrier layer is 1:(2.5-5).

[0031] As an improvement of the above scheme, in the first period of the fourth light blue light multi-quantum well sublayer, the fourth InGaN multi-quantum well layer in the first period is a non-doped InGaN multi-quantum well layer; in the second period of the fourth light blue light multi-quantum well sublayer, the fourth InGaN multi-quantum well layer in the second period is a Mg-doped InGaN multi-quantum well layer, and the doping concentration of Mg is 3.6×1018 / cm 3 ~5.2×10 19 / cm 3 .

[0032] As an improvement of the above solution, the fourth multi-quantum barrier layer is a superlattice structure formed by GaN layers and InGaN layers that are periodically and alternately grown from bottom to top, and the number of periods is 2 to 10;

[0033] The GaN layer is a non-doped GaN layer with a thickness of 0.5nm to 3nm;

[0034] The InGaN layer is a Mg-doped InGaN layer, the In component is x5, 0.01≤x5≤0.12; the Mg doping concentration is 5.0×10 18 / cm 3 ~7.6×10 19 / cm 3 ;

[0035] The thickness of the InGaN layer is 0.5nm~3nm.

[0036] As an improvement of the above solution, in the multi-quantum well light-emitting layer, x1≤x2≤x3≥x4;

[0037] The growth temperature of the first InGaN multi-quantum well layer is T1, the growth temperature of the second InGaN multi-quantum well layer is T2, the growth temperature of the third InGaN multi-quantum well layer is T3, and the growth temperature of the fourth InGaN multi-quantum well layer is T4, T1≥T2≥T3≤T4.

[0038] The second aspect of the present invention further provides a method for preparing the epitaxial structure of the blue light Micro-LED, comprising:

[0039] providing a substrate;

[0040] growing a buffer layer on the substrate;

[0041] growing an N-type semiconductor layer on the buffer layer;

[0042] growing a low-temperature stress release layer on the N-type semiconductor layer;

[0043] growing a multi-quantum well light-emitting layer on the low-temperature stress release layer;

[0044] growing an electron blocking layer on the multi-quantum well light-emitting layer;

[0045] growing a P-type semiconductor layer on the electron blocking layer;

[0046] The multi-quantum well light-emitting layer includes a first light blue multi-quantum well sublayer, a second light blue multi-quantum well sublayer, a third blue multi-quantum well sublayer and a fourth light blue multi-quantum well sublayer which are stacked and grown in sequence from bottom to top.

[0047] The implementation of the present invention has the following beneficial effects:

[0048] The multi-quantum well light-emitting layer described in the present invention includes a first light blue light multi-quantum well sublayer, a second light blue light multi-quantum well sublayer, a third blue light multi-quantum well sublayer and a fourth light blue light multi-quantum well sublayer, which are stacked and grown in sequence from bottom to top, and the structures of the first light blue light multi-quantum well sublayer, the second light blue light multi-quantum well sublayer, the third blue light multi-quantum well sublayer and the fourth light blue light multi-quantum well sublayer are adjusted and designed, which can reduce the stress during the growth of InGaN quantum wells, significantly improve the quality of the multi-quantum well light-emitting layer, and at the same time improve the hole injection efficiency of the P-type semiconductor layer, thereby improving the luminous efficiency, yield and other performance of the Micro-LED chip at low operating current density, making it suitable for small size, low current and low power blue light Micro-LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 : A schematic diagram of the epitaxial structure of a blue light Micro-LED in the present invention;

[0050] Figure 2 : Schematic diagram of the structure of the multi-quantum well light-emitting layer in the present invention.

[0051] Reference numerals:

[0052] 100-substrate; 200-buffer layer; 300-N-type semiconductor layer; 400-low-temperature stress release layer; 500-multi-quantum well light-emitting layer; 510-first light blue light multi-quantum well sublayer; 511-first InGaN multi-quantum well layer; 512-first multi-quantum well composite barrier layer; 520-second light blue light multi-quantum well sublayer; 521-second InGaN multi-quantum well layer; 522-second multi-quantum well composite barrier layer; 530-third blue light multi-quantum well sublayer; 531-third InGaN multi-quantum well layer; 532-third Si-doped GaN multi-quantum barrier layer; 540-fourth light blue light multi-quantum well sublayer; 541-non-doped InGaN multi-quantum well layer; 542-first period fourth multi-quantum barrier layer; 543-Mg-doped InGaN multi-quantum well layer; 544-second period fourth multi-quantum barrier layer; 600-electron blocking layer; 700-P-type semiconductor layer. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail with specific embodiments below.

[0054] In order to solve the above problems, the first aspect of the present invention provides an epitaxial structure of a blue light Micro-LED, see Figure 1 , including 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, an electron blocking layer 600 and a P-type semiconductor layer 700 sequentially stacked on the substrate 100.

[0055] See also Figure 2 The multi-quantum well light-emitting layer 500 includes a first light blue light multi-quantum well sublayer 510, a second light blue light multi-quantum well sublayer 520, a third blue light multi-quantum well sublayer 530 and a fourth light blue light multi-quantum well sublayer 540 which are stacked and grown in sequence from bottom to top.

[0056] In this aspect, the third blue light multi-quantum well sublayer 530 is used as the light-emitting unit, and the epitaxial structure of the blue light Micro-LED suitable for small size, low current density and low power is redesigned. The blue light Micro-LED chip prepared by the present invention can significantly improve the quality of the multi-quantum well light-emitting layer 500, and at the same time improve the hole injection efficiency of the P-type semiconductor layer 700, thereby improving the luminous efficiency, yield and other performance of the Micro-LED chip at low operating current density.

[0057] Among them, the first light blue light multi-quantum well sublayer 510 is a superlattice structure of a first InGaN multi-quantum well layer 511 and a first multi-quantum well composite barrier layer 512 that are periodically and alternately grown from bottom to top, with the number of periods being 2 to 6, exemplarily 2, 3, 4, 5, and 6.

[0058] Preferably, the first InGaN multi-quantum well layer 511 is an undoped single-layer structure or a multi-layer structure, and the In component is x1, 0.08≤x1≤0.15; x1 is exemplarily 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, but is not limited thereto.

[0059] Further, the thickness of the first InGaN multi-quantum well layer 511 is 2.2 nm to 3.8 nm, and exemplary thicknesses are 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, 3 nm, 3.2 nm, 3.4 nm, 3.6 nm, and 3.8 nm, but are not limited thereto.

[0060] Preferably, the first multi-quantum well composite barrier layer 512 includes a first Si-doped GaN barrier layer, a first AlGaN barrier layer and a first GaN barrier layer which are sequentially stacked and grown from bottom to top;

[0061] Furthermore, the thickness of the first Si-doped GaN barrier layer is 1 nm to 8 nm, and the Si doping concentration is 1.2×10 17 / cm 3 ~7.6×10 18 / cm 3 ; Exemplary thicknesses are 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, but are not limited thereto; an exemplary doping concentration is 1.2×10 17 / cm 3 , 3.2×10 17 / cm 3 , 5.2×10 17 / cm 3 , 7.2×10 17 / cm 3 , 9.2×10 17 / cm 3 , 1.2×10 18 / cm 3 , 3.2×10 18 / cm 3 , 5.2×10 18 / cm 3 , 7.2×10 18 / cm 3 , 7.6×10 18 / cm 3 , but not limited to this.

[0062] Further, the Al component in the first AlGaN barrier layer is y1, 0.02≤y1≤0.36, y1 is exemplarily 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.36, but not limited thereto. The thickness of the first AlGaN barrier layer is 0.5nm~6.6nm, and the exemplary thickness is 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 6.6nm, but not limited thereto.

[0063] Further, the thickness of the first GaN barrier layer is 1 nm to 8 nm, and exemplary thicknesses are 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, and 8 nm, but are not limited thereto.

[0064] Furthermore, the total thickness of the first multi-quantum well composite barrier layer 512 is 7nm~16nm; the thickness ratio of the first InGaN multi-quantum well layer 511 to the first multi-quantum well composite barrier layer 512 is 1:(2.5~5), and exemplary ones are 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, but not limited thereto.

[0065] Among them, the second light blue light multi-quantum well sublayer 520 is a superlattice structure of a second InGaN multi-quantum well layer 521 and a second multi-quantum well composite barrier layer 522 that are periodically and alternately grown from bottom to top, with a period number of 1 to 5, and exemplary period numbers are 1, 2, 3, 4, and 5.

[0066] Preferably, the second InGaN multi-quantum well layer 521 is an undoped single-layer structure or a multi-layer structure, and the In component ratio is x2, 0.1≤x2≤0.18, and x2 is exemplarily 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, but is not limited thereto.

[0067] Further, the thickness of the second InGaN multi-quantum well layer 521 is 2.2 nm to 3.8 nm, and exemplary thicknesses are 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, 3 nm, 3.2 nm, 3.4 nm, 3.6 nm, and 3.8 nm, but are not limited thereto.

[0068] The structure of the second multi-quantum well composite barrier layer 522 in the present invention is the same as that of the first multi-quantum well composite barrier layer 512. Both the first multi-quantum well composite barrier layer 512 and the second multi-quantum well composite barrier layer 522 include a Si-doped GaN barrier layer, an AlGaN barrier layer and a GaN barrier layer that are stacked and grown in sequence from bottom to top. The design of this structure and process can effectively bind electrons in front of the third blue light multi-quantum well sublayer 530, blocking electrons and reducing the electron movement rate, thereby improving the electron-hole matching degree in the third blue light multi-quantum well sublayer 530, improving the light efficiency of the Micro-LED under low operating current density, and also preventing electrons from being injected into the P-type semiconductor layer 700 to cause electron leakage, thereby improving the yield rate and other performance of the Micro-LED.

[0069] Furthermore, the second multi-quantum well composite barrier layer 522 includes a second Si-doped GaN barrier layer, a second AlGaN barrier layer and a second GaN barrier layer which are sequentially stacked and grown from bottom to top.

[0070] Furthermore, the thickness of the second Si-doped GaN barrier layer is 1 nm to 8 nm, and the Si doping concentration is 1.2×10 17 / cm 3 ~7.6×1018 / cm 3 ; Exemplary thicknesses are 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, but are not limited thereto; an exemplary doping concentration is 1.2×10 17 / cm 3 , 3.2×10 17 / cm 3 , 5.2×10 17 / cm 3 , 7.2×10 17 / cm 3 , 9.2×10 17 / cm 3 , 1.2×10 18 / cm 3 , 3.2×10 18 / cm 3 , 5.2×10 18 / cm 3 , 7.2×10 18 / cm 3 , 7.6×10 18 / cm 3 , but not limited to this.

[0071] Furthermore, the Al component in the second AlGaN barrier layer is y2, 0.02≤y2≤0.36; y2 is exemplarily 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.36, but not limited thereto. The thickness of the second AlGaN barrier layer is 0.5nm~6.6nm, and the exemplary thickness is 0.5nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 6.6nm, but not limited thereto.

[0072] Furthermore, the thickness of the second GaN barrier layer is 1 nm to 8 nm, and exemplary thicknesses are 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, and 8 nm, but are not limited thereto.

[0073] Furthermore, the total thickness of the second multi-quantum well composite barrier layer 522 is 7nm~16nm; the thickness ratio of the second InGaN multi-quantum well layer 521 to the second multi-quantum well composite barrier layer 522 is 1:(2.5~5), and exemplary ones are 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, but not limited thereto.

[0074] Among them, the third blue light multi-quantum well sublayer 530 is a superlattice structure of a third InGaN multi-quantum well layer 531 and a third Si-doped GaN multi-quantum barrier layer 532 that are periodically and alternately grown from bottom to top; the number of periods is 2 to 8, and exemplary ones are 2, 3, 4, 5, 6, 7, and 8.

[0075] Preferably, the third InGaN multi-quantum well layer 531 is an undoped single-layer structure or a multi-layer structure, and the In component ratio is x3, 0.13≤x3≤0.21, and x3 is exemplarily 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, but not limited thereto.

[0076] Further, the thickness of the third InGaN multi-quantum well layer 531 is 2.5 nm to 4.2 nm, and exemplary thicknesses are 2.5 nm, 2.7 nm, 2.9 nm, 3.1 nm, 3.3 nm, 3.5 nm, 3.7 nm, 3.9 nm, 4 nm, and 4.2 nm, but are not limited thereto.

[0077] Preferably, the third Si-doped GaN multi-quantum barrier layer 532 is a single-layer structure or a multi-layer structure doped with Si element, and the doping concentration of Si is 1.2×10 17 / cm 3 ~8.6×10 17 / cm 3 , an exemplary doping concentration is 1.2×10 17 / cm 3 , 3.2×10 17 / cm 3 , 5.2×10 17 / cm 3 , 7.2×10 17 / cm 3 , 8.6×10 17 / cm 3 , but not limited to this.

[0078] Further, the thickness of the third Si-doped GaN multi-quantum barrier layer 532 is 6.5 nm to 13.6 nm, and exemplary thicknesses are 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, 10.5 nm, 11.5 nm, 12.5 nm, 13.5 nm, and 13.6 nm, but are not limited thereto.

[0079] Furthermore, a thickness ratio of the third InGaN multi-quantum well layer 531 to the third Si-doped GaN multi-quantum barrier layer 532 is 1:(2.4-4.5), exemplarily 1:2.4, 1:3, 1:3.4, 1:4, 1:4.4, 1:4.5, but not limited thereto.

[0080] The fourth light blue multi-quantum well sublayer 540 is a superlattice structure of a fourth InGaN multi-quantum well layer and a fourth multi-quantum barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2.

[0081] Preferably, the fourth InGaN multi-quantum well layer is a non-doped InGaN multi-quantum well layer and / or a Mg-doped InGaN multi-quantum well layer; the thickness of the fourth InGaN multi-quantum well layer is 2.2nm~3.8nm, and exemplary thicknesses are 2.2nm, 2.4nm, 2.6nm, 2.8nm, 3nm, 3.2nm, 3.4nm, 3.6nm, and 3.8nm, but are not limited thereto.

[0082] Specifically, the fourth light blue multi-quantum well sublayer 540 includes a non-InGaN multi-quantum well layer 541, a first-period fourth multi-quantum barrier layer 542, a Mg-doped InGaN multi-quantum well layer 543 and a second-period fourth multi-quantum barrier layer 544 stacked in sequence from bottom to top.

[0083] In the non-doped InGaN multi-quantum well layer 541, the In component is x4, 0.08≤x4≤0.18; x4 is exemplarily 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, but is not limited thereto. In the Mg-doped InGaN multi-quantum well layer 543, the Mg doping concentration is 3.6×10 18 / cm 3 ~5.2×10 19 / cm 3 , an exemplary doping concentration is 3.6×10 18 / cm 3 , 5.6×10 18 / cm 3 , 7.6×10 18 / cm 3 , 9.6×10 18 / cm3 , 1.6×10 19 / cm 3 , 3.6×10 19 / cm 3 , 5.2×10 19 / cm 3 , but not limited to this.

[0084] Preferably, the fourth multi-quantum barrier layer is a superlattice structure formed by GaN layers and InGaN layers that are periodically grown alternately from bottom to top, and the number of periods is 2 to 10. Specifically, the first-period fourth multi-quantum barrier layer 542 is a superlattice structure formed by GaN layers and InGaN layers that are periodically grown alternately from bottom to top, and the number of periods is 2 to 10; the second-period fourth multi-quantum barrier layer 544 is a superlattice structure formed by GaN layers and InGaN layers that are periodically grown alternately from bottom to top, and the number of periods is 2 to 10.

[0085] Further, the GaN layer is a non-doped GaN layer with a thickness of 0.5 nm to 3 nm, and exemplary thicknesses are 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, and 3 nm, but are not limited thereto.

[0086] Furthermore, the InGaN layer is a Mg-doped InGaN layer, the In composition is x5, 0.01≤x5≤0.12; the Mg doping concentration is 5.0×10 18 / cm 3 ~7.6×10 19 / cm 3 ; x5 is 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.12, but not limited thereto; an exemplary doping concentration is 5.0×10 18 / cm 3 , 7.0×10 18 / cm 3 9.0×10 18 / cm 3 , 1.0×10 19 / cm 3 , 3.0×10 19 / cm 3 , 5.0×10 19 / cm 3 , 7.0×10 19 / cm 3 , 7.6×10 19 / cm 3 , but not limited to this.

[0087] Furthermore, the thickness of the InGaN layer is 0.5 nm to 3 nm, and exemplary thicknesses are 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, and 3 nm, but are not limited thereto.

[0088] Furthermore, the total thickness of the fourth multi-quantum barrier layer is 6.5 nm to 15 nm.

[0089] In some specific and preferred embodiments, the thickness ratio of the fourth InGaN multi-quantum well layer to the fourth multi-quantum barrier layer is 1:(2.5-5), exemplarily 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, but not limited thereto.

[0090] In the present invention, the thickness ratio of the InGaN multi-quantum well layer to the barrier layer in the first light blue light multi-quantum well sublayer 510, the second light blue light multi-quantum well sublayer 520, the third blue light multi-quantum well sublayer 530 and the fourth light blue light multi-quantum well sublayer 540 is strictly controlled, and the thickness of the multi-quantum well composite barrier layer is increased, so as to enhance the carrier confinement capability of the InGaN multi-quantum well layer and improve the crystal quality of the low-temperature grown multi-quantum well light-emitting layer 500, thereby improving the luminous efficiency. However, as the thickness of the barrier layer continues to increase, the migration of carriers in each quantum well layer is restricted, and stress accumulation is formed, which increases the piezoelectric polarization electric field strength, thereby causing wavelength red shift and reduced luminescence efficiency; and through a large number of experiments, it can be obtained that the thickness ratios of the InGaN multi-quantum well layer and the barrier layer in the first light blue light multi-quantum well sublayer 510, the second light blue light multi-quantum well sublayer 520 and the fourth light blue light multi-quantum well sublayer 540 are all controlled at 1: (2.5~5), and the thickness ratio of the third InGaN multi-quantum well layer 531 and the third Si-doped GaN multi-quantum barrier layer 532 in the third blue light multi-quantum well sublayer 530 is within the range of 1: (2.4~4.5), and the different layers work synergistically with each other, and the luminescence efficiency of the device is optimal.

[0091] The fourth light blue multi-quantum well sublayer 540 is a superlattice structure of a fourth InGaN multi-quantum well layer and a fourth multi-quantum barrier layer that are periodically and alternately grown from bottom to top. The fourth multi-quantum barrier layer is a superlattice structure formed by a GaN layer and an InGaN layer that are periodically and alternately grown from bottom to top. The fourth multi-quantum barrier layer adopts the structure and process design of GaN / InGaN superlattice material. The low-barrier InGaN material makes it easier for holes in the P-type semiconductor layer 700 to be injected into the third blue multi-quantum well sublayer 530 to participate in luminescence, which can effectively improve the injection efficiency of carrier holes. At the same time, the InGaN material is low-doped with Mg elements, which can provide some holes, thereby improving the luminous efficiency of the Micro-LED chip at low operating current density.

[0092] Preferably, in the multi-quantum well light-emitting layer 500, x1≤x2≤x3≥x4; the InGaN material of the multi-quantum well light-emitting layer 500 forms an InGaN / barrier layer superlattice structure in which the In component increases and then decreases in sequence. This structure and process design can effectively reduce the lattice mismatch stress between the third blue light multi-quantum well InGaN material and the barrier layer material, and improve the crystal quality of the multi-quantum well light-emitting layer 500 under low operating current density, thereby improving the radiation recombination efficiency of the multi-quantum well light-emitting layer 500 and reducing the operating voltage.

[0093] Furthermore, the growth temperature of the first InGaN multi-quantum well layer 511 is T1, the growth temperature of the second InGaN multi-quantum well layer 521 is T2, the growth temperature of the third InGaN multi-quantum well layer 531 is T3, and the growth temperature of the fourth InGaN multi-quantum well layer is T4, T1≥T2≥T3≤T4. The growth temperature of the InGaN material in the first light blue multi-quantum well sublayer 510, the second light blue multi-quantum well sublayer 520, and the fourth light blue multi-quantum well sublayer 540 in the multi-quantum well light-emitting layer 500 is higher than the growth temperature of the InGaN material in the third blue multi-quantum well sublayer 530. The high-temperature growth of InGaN material has high atomic mobility and is more inclined to two-dimensional material growth. The defects in the InGaN material will be significantly reduced, and it is easier to obtain high-quality InGaN material. At the same time, the first light blue multi-quantum well sublayer 510, the second light blue multi-quantum well sublayer 520, and the fourth light blue multi-quantum well sublayer 540 are The InGaN material in the well sublayer 520 and the fourth light blue multi-quantum well sublayer 540 has a lower In component than that in the third blue multi-quantum well sublayer 530. The lattice mismatch stress between the InGaN material and the GaN material in the multi-quantum well layer is reduced, and the defects caused by the large mismatch stress are reduced, which 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 radiation recombination efficiency of the multi-quantum well layer, thereby improving the luminous efficiency and yield of the Micro-LED at low operating current density.

[0094] Furthermore, the growth temperature of the first InGaN multi-quantum well layer 511 is 780℃~920℃, and the growth pressure is 50torr~300torr; the growth temperature of the first Si-doped GaN barrier layer is 800℃~920℃, and the growth pressure is 50torr~300torr; the growth temperature of the first AlGaN barrier layer is 800℃~920℃, and the growth pressure is 50torr~300torr; the growth temperature of the first GaN barrier layer is 800℃~920℃, and the growth pressure is 50torr~300torr.

[0095] The growth temperature of the second InGaN multi-quantum well layer 521 is 765°C~900°C, and the growth pressure is 50torr~300torr; the growth temperature of the second Si-doped GaN barrier layer is 800°C~920°C, and the growth pressure is 50torr~300torr; the growth temperature of the second AlGaN barrier layer is 800°C~920°C, and the growth pressure is 50torr~300torr; the growth temperature of the second GaN barrier layer is 800°C~920°C, and the growth pressure is 50torr~300torr.

[0096] The growth temperature of the third InGaN multi-quantum well layer 531 is 750° C. to 880° C., and the growth pressure is 50 torr to 300 torr; the growth temperature of the third Si-doped GaN multi-quantum barrier layer 532 is 810° C. to 920° C., and the growth pressure is 50 torr to 300 torr.

[0097] The growth temperature of the fourth InGaN multi-quantum well layer is 765°C~920°C, and the growth pressure is 50torr~300torr; the growth temperature of the GaN layer is 810°C~920°C, and the growth pressure is 50torr~300torr; the growth temperature of the InGaN is 810°C~920°C, and the growth pressure is 50torr~300torr.

[0098] Accordingly, the present invention also provides a method for preparing the epitaxial structure of the blue light Micro-LED, comprising:

[0099] (1) Providing a substrate 100;

[0100] (2) growing a buffer layer 200 on the substrate 100;

[0101] (3) Growing an N-type semiconductor layer 300 on the buffer layer 200;

[0102] (4) growing a low-temperature stress release layer 400 on the N-type semiconductor layer 300;

[0103] (5) growing a multi-quantum well light-emitting layer 500 on the low-temperature stress release layer 400;

[0104] (6) growing an electron blocking layer 600 on the multi-quantum well light-emitting layer 500;

[0105] (7) Growing a P-type semiconductor layer 700 on the electron blocking layer 600;

[0106] The multi-quantum well light-emitting layer 500 includes a first light blue multi-quantum well sublayer 510, a second light blue multi-quantum well sublayer 520, a third blue multi-quantum well sublayer 530 and a fourth light blue multi-quantum well sublayer 540 which are stacked from bottom to top.

[0107] In the present invention, the materials and thicknesses of the buffer layer 200, the N-type semiconductor layer 300, the low-temperature stress release layer 400, the electron blocking layer 600, and the P-type semiconductor layer 700 can be selected from the conventional ranges in the art.

[0108] It should be noted that the present invention uses Veeco C4 MOCVD (Metal Organic Chemical Vapor Deposition) equipment to achieve the growth method of the epitaxial wafer. High-purity H2 (hydrogen) or high-purity N2 (nitrogen) or a mixed gas of high-purity H2 and high-purity N2 is used as the carrier gas. The N source is high-purity NH3, the Al source is TMAl (trimethylaluminum), the Ga source is TMGa (trimethylgallium), the In source is TMIn (trimethylindium), the Si source is SiH4, and the Mg source is CP2Mg.

[0109] The present invention will be further described below with specific embodiments:

[0110] Example 1

[0111] The present embodiment provides an epitaxial structure of a blue light Micro-LED, including a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress release layer, a multi-quantum well light-emitting layer, an electron blocking layer and a P-type semiconductor layer stacked in sequence on the substrate.

[0112] The multi-quantum well light-emitting layer includes a first light blue multi-quantum well sublayer, a second light blue multi-quantum well sublayer, a third blue multi-quantum well sublayer and a fourth light blue multi-quantum well sublayer, which are stacked and grown in sequence from bottom to top; wherein,

[0113] The first light blue multi-quantum well sublayer is a superlattice structure of a first InGaN multi-quantum well layer and a first multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top, with a period number of 4;

[0114] The first InGaN multi-quantum well layer is a non-doped single-layer structure, the In component is x1, x1=0.11, and the thickness is 3nm;

[0115] The first multi-quantum well composite barrier layer includes a first Si-doped GaN barrier layer, a first AlGaN barrier layer and a first GaN barrier layer which are sequentially stacked from bottom to top; the thickness of the first Si-doped GaN barrier layer is 4.5 nm, and the doping concentration of Si is 9.5×10 17 / cm3 ; The Al component in the first AlGaN barrier layer is y1, y1=0.19; the thickness is 3.5nm; the thickness of the first GaN barrier layer is 4.5nm.

[0116] The second light blue multi-quantum well sublayer is a superlattice structure of a second InGaN multi-quantum well layer and a second multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top, with a period number of 3;

[0117] The second InGaN multi-quantum well layer is a non-doped single-layer structure, the In component ratio is x2, x2=0.15, and the thickness is 3nm;

[0118] The second multi-quantum well composite barrier layer includes a second Si-doped GaN barrier layer, a second AlGaN barrier layer and a second GaN barrier layer which are sequentially stacked from bottom to top; the thickness of the second Si-doped GaN barrier layer is 4.5 nm, and the doping concentration of Si is 9.5×10 17 / cm 3 ; The Al component in the second AlGaN barrier layer is y2, y2=0.19, and the thickness is 3.6nm; the thickness of the second GaN barrier layer is 4.5nm.

[0119] The third blue light multi-quantum well sublayer is a superlattice structure of a third InGaN multi-quantum well layer and a third Si-doped GaN multi-quantum barrier layer that are periodically and alternately grown from bottom to top; the number of periods is 5.

[0120] The third InGaN multi-quantum well layer is a non-doped single-layer structure, the In component ratio is x3, x3=0.17, and the thickness is 3.4nm;

[0121] The third Si-doped GaN multi-quantum barrier layer is a single-layer structure doped with Si element, and the doping concentration of Si is 4.9×10 17 / cm 3 , with a thickness of 10.1nm.

[0122] The fourth light blue light multi-quantum well sublayer is a superlattice structure of a fourth InGaN multi-quantum well layer and a fourth multi-quantum barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2, specifically including a non-doped InGaN multi-quantum well layer, a first-period fourth multi-quantum barrier layer, a Mg-doped InGaN multi-quantum well layer, and a second-period fourth multi-quantum barrier layer stacked in sequence from bottom to top.

[0123] The non-doped InGaN multi-quantum well layer has an In component of x4, x4=0.13, and a thickness of 3 nm. The first period fourth multi-quantum barrier layer is a superlattice structure formed by GaN layers and InGaN layers that are periodically grown alternately from bottom to top, with a period number of 4. The GaN layer is a non-doped GaN layer with a thickness of 1.8 nm. The InGaN layer is a Mg-doped InGaN layer, with an In component of x5, x5=0.07, and a Mg doping concentration of 1.0×10 19 / cm 3 , thickness is 1.6nm, and the total thickness is 13.6nm.

[0124] In the Mg-doped InGaN multi-quantum well layer, the Mg doping concentration is 8.5×10 18 / cm 3 , In component is x4, x4=0.13, and thickness is 3nm; the fourth multi-quantum barrier layer of the second period is a superlattice structure formed by GaN layer and InGaN layer grown periodically and alternately from bottom to top, with a period number of 4, the GaN layer is an undoped GaN layer with a thickness of 1.8nm; the InGaN layer is a Mg-doped InGaN layer, In component is x5, x5=0.07, and Mg doping concentration is 1.0×10 19 / cm 3 , thickness is 1.6nm, and the total thickness is 13.6nm.

[0125] The preparation method is as follows:

[0126] (1) Providing a substrate;

[0127] (2) growing a buffer layer on the substrate;

[0128] (3) growing an N-type semiconductor layer on the buffer layer;

[0129] (4) growing a low-temperature stress release layer on the N-type semiconductor layer;

[0130] (5) growing a multi-quantum well light-emitting layer on the low-temperature stress release layer;

[0131] The multi-quantum well light-emitting layer comprises a first light blue multi-quantum well sublayer, a second light blue multi-quantum well sublayer, a third blue multi-quantum well sublayer and a fourth light blue multi-quantum well sublayer which are stacked and grown in sequence from bottom to top.

[0132] In the first light blue multi-quantum well sublayer;

[0133] The growth temperature T1 of the first InGaN multi-quantum well layer is 830°C and the growth pressure is 150torr; the growth temperature T1 of the first Si-doped GaN barrier layer is 860°C and the growth pressure is 150torr; the growth temperature T2 of the first AlGaN barrier layer is 860°C and the growth pressure is 150torr; the growth temperature T3 of the first GaN barrier layer is 860°C and the growth pressure is 150torr;

[0134] In the second light blue multi-quantum well sublayer;

[0135] The growth temperature T2 of the second InGaN multi-quantum well layer is 800°C and the growth pressure is 150torr; the growth temperature T2 of the second Si-doped GaN barrier layer is 860°C and the growth pressure is 150torr; the growth temperature T2 of the second AlGaN barrier layer is 860°C and the growth pressure is 150torr; the growth temperature T2 of the second GaN barrier layer is 860°C and the growth pressure is 150torr;

[0136] In the third blue light multi-quantum well sublayer;

[0137] The growth temperature T3 of the third InGaN multi-quantum well layer is 770° C., and the growth pressure is 150 torr; the growth temperature T3 of the third Si-doped GaN multi-quantum barrier layer is 860° C., and the growth pressure is 150 torr.

[0138] In the fourth light blue multi-quantum well sublayer;

[0139] The growth temperature T4 of the fourth InGaN multi-quantum well layer is 830° C., and the growth pressure is 150 torr; the growth temperature T4 of the GaN layer is 860° C., and the growth pressure is 150 torr; the growth temperature T4 of the InGaN layer is 860° C., and the growth pressure is 150 torr.

[0140] (6) growing an electron blocking layer on the multi-quantum well light-emitting layer;

[0141] (7) Growing a P-type semiconductor layer on the electron blocking layer.

[0142] Example 2

[0143] This embodiment provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Embodiment 1, except that:

[0144] x1=0.15, x2=0.1, x3=0.17, x4=0.13.

[0145] Example 3

[0146] This embodiment provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Embodiment 1, except that:

[0147] x1=0.11, x2=0.15, x3=0.17, x4=0.18.

[0148] Example 4

[0149] This embodiment provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Embodiment 1, except that:

[0150] The thickness of the first InGaN multi-quantum well layer is 2 nm;

[0151] The thickness of the first Si-doped GaN barrier layer is 4.5 nm, the thickness of the first AlGaN barrier layer is 3.5 nm, and the thickness of the first GaN barrier layer is 4.5 nm.

[0152] The thickness of the second InGaN multi-quantum well layer is 2 nm;

[0153] The thickness of the second Si-doped GaN barrier layer is 4.5 nm, the thickness of the second AlGaN barrier layer is 3.5 nm, and the thickness of the second GaN barrier layer is 4.5 nm.

[0154] Example 5

[0155] This embodiment provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Embodiment 1, except that:

[0156] The thickness of the third InGaN multi-quantum well layer is 2.5 nm, and the thickness of the third Si-doped GaN multi-quantum barrier layer is 13.5 nm.

[0157] The thickness of the fourth InGaN multi-quantum well layer is 3 nm; the fourth multi-quantum barrier layer is a superlattice structure formed by GaN layers and InGaN layers that are periodically and alternately grown from bottom to top, with a period number of 6 and a total thickness of 20.4 nm.

[0158] Example 6

[0159] This embodiment provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Embodiment 1, except that:

[0160] The growth temperature T1 of the first InGaN multi-quantum well layer is 800°C, the growth temperature T2 of the second InGaN multi-quantum well layer is 830°C, the growth temperature T3 of the third InGaN multi-quantum well layer is 770°C, and the growth temperature T4 of the fourth InGaN multi-quantum well layer is 800°C.

[0161] Comparative Example 1

[0162] This comparative example provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Example 1, except that:

[0163] The multi-quantum well layer is a periodic structure of alternately stacked InGaN quantum well layers and GaN quantum barrier layers, with a stacking period number of 8. In a single period, the In component of the InGaN quantum well layer is 0.17, the thickness of the InGaN quantum well layer is 3.4 nm, and the thickness of the GaN quantum barrier layer is 13 nm.

[0164] Comparative Example 2

[0165] This comparative example provides an epitaxial structure of a blue light Micro-LED, which is basically the same as that of Example 1, except that:

[0166] The first light blue multi-quantum well sublayer is a first InGaN multi-quantum well layer and a first multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top;

[0167] The second light blue multi-quantum well sublayer is a second InGaN multi-quantum well layer and a second multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top;

[0168] The third blue light multi-quantum well sublayer is a third InGaN multi-quantum well layer and a third Si-doped GaN multi-quantum barrier layer that are periodically and alternately grown from bottom to top;

[0169] The fourth light blue multi-quantum well sublayer is a fourth InGaN multi-quantum well layer and a fourth multi-quantum barrier layer that are periodically and alternately grown from bottom to top.

[0170] The epitaxial structures obtained in the embodiments and comparative examples were made into 20μm×20μm Micro-LED chips and tested at 3μA / 10μA / 30μA currents. The luminous efficiency improvement, luminous wavelength / nm, WD STD (nm) of the chips and the twin crystal (002) arcsec and (102) arcsec of the epitaxial wafer XRD test were measured. The luminous efficiency improvement was calculated based on comparative example 1.

[0171] The performance test results are shown in Table 1.

[0172] Table 1 Performance test results of examples and comparative examples

[0173]

[0174] From the above results, it can be seen that the multi-quantum well light-emitting layer arranged in the present invention includes a first light blue light multi-quantum well sublayer, a second light blue light multi-quantum well sublayer, a third blue light multi-quantum well sublayer and a fourth light blue light multi-quantum well sublayer which are stacked and grown from bottom to top, and each layer is a superlattice structure. The redesign of the epitaxial structure can significantly improve the crystal quality of the multi-quantum well light-emitting layer, and at the same time improve the hole injection efficiency of the P-type semiconductor layer, thereby improving the luminous efficiency, luminescence stability and other performances of the Micro-LED chip at low operating current density, making it suitable for small size, low current and low power blue light Micro-LED.

[0175] 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 blue light Micro-LED epitaxial structure, characterized in that: It comprises a substrate, a buffer layer, an N-type semiconductor layer, a low-temperature stress release layer, a multi-quantum well light-emitting layer, an electron blocking layer and a P-type semiconductor layer which are sequentially stacked on the substrate; The multi-quantum well light-emitting layer comprises a first light blue multi-quantum well sublayer, a second light blue multi-quantum well sublayer, a third blue multi-quantum well sublayer and a fourth light blue multi-quantum well sublayer, which are sequentially stacked from bottom to top; The first light blue multi-quantum well sublayer is a superlattice structure of a first InGaN multi-quantum well layer and a first multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2 to 6; The second light blue multi-quantum well sublayer is a superlattice structure of a second InGaN multi-quantum well layer and a second multi-quantum well composite barrier layer that are periodically and alternately grown from bottom to top, with a period number of 1 to 5; The third blue light multi-quantum well sublayer is a superlattice structure of a third InGaN multi-quantum well layer and a third Si-doped GaN multi-quantum barrier layer that are periodically and alternately grown from bottom to top; the number of periods is 2 to 8; The fourth light blue multi-quantum well sublayer is a superlattice structure of a fourth InGaN multi-quantum well layer and a fourth multi-quantum barrier layer that are periodically and alternately grown from bottom to top, with a period number of 2; The first InGaN multi-quantum well layer is a non-doped single-layer structure or a multi-layer structure, and the In component is x1, 0.08≤x1≤0.15; the thickness of the first InGaN multi-quantum well layer is 2.2nm~3.8nm; The second InGaN multi-quantum well layer is a non-doped single-layer structure or a multi-layer structure, and the In component ratio is x2, 0.1≤x2≤0.18; the thickness of the second InGaN multi-quantum well layer is 2.2nm~3.8nm; The third InGaN multi-quantum well layer is a non-doped single-layer structure or a multi-layer structure, and the In component ratio is x3, 0.13≤x3≤0.21; the thickness of the third InGaN multi-quantum well layer is 2.5nm~4.2nm; The fourth InGaN multi-quantum well layer is a non-doped InGaN multi-quantum well layer and / or a Mg-doped InGaN multi-quantum well layer, and the In component is x4, 0.08≤x4≤0.18; the thickness of the fourth InGaN multi-quantum well layer is 2.2nm~3.8nm; In the multi-quantum well light-emitting layer, x1≤x2≤x3≥x4; The first multi-quantum well composite barrier layer includes a first Si-doped GaN barrier layer, a first AlGaN barrier layer and a first GaN barrier layer which are sequentially stacked and grown from bottom to top; The thickness of the first Si-doped GaN barrier layer is 1 nm to 8 nm, and the Si doping concentration is 1.2×10 17 / cm 3 ~7.6×10 18 / cm 3 ; The Al component in the first AlGaN barrier layer is y1, 0.02≤y1≤0.36; The thickness of the first AlGaN barrier layer is 0.5nm~6.6nm; The thickness of the first GaN barrier layer is 1nm~8nm; The second multi-quantum well composite barrier layer includes a second Si-doped GaN barrier layer, a second AlGaN barrier layer and a second GaN barrier layer which are sequentially stacked and grown from bottom to top; The thickness of the second Si-doped GaN barrier layer is 1 nm to 8 nm, and the Si doping concentration is 1.2×10 17 / cm 3 ~7.6×10 18 / cm 3 ; The Al component in the second AlGaN barrier layer is y2, 0.02≤y2≤0.36; the thickness of the second AlGaN barrier layer is 0.5nm~6.6nm; The thickness of the second GaN barrier layer is 1 nm to 8 nm; The fourth multi-quantum barrier layer is a superlattice structure formed by GaN layers and InGaN layers that are periodically and alternately grown from bottom to top, with a period number of 2 to 10; The GaN layer is a non-doped GaN layer with a thickness of 0.5nm to 3nm; The InGaN layer is a Mg-doped InGaN layer, the In component is x5, 0.01≤x5≤0.12; the Mg doping concentration is 5.0×10 18 / cm 3 ~7.6×10 19 / cm 3 ; The thickness of the InGaN layer is 0.5nm~3nm.

2. The blue light Micro-LED epitaxial structure according to claim 1, characterized in that: The total thickness of the first multi-quantum well composite barrier layer is 7nm-16nm; The total thickness of the second multi-quantum well composite barrier layer is 7nm-16nm; The thickness ratio of the first InGaN multi-quantum well layer to the first multi-quantum well composite barrier layer is 1:(2.5-5); The thickness ratio of the second InGaN multi-quantum well layer to the second multi-quantum well composite barrier layer is 1:(2.5-5).

3. The blue light Micro-LED epitaxial structure according to claim 1, characterized in that: The third Si-doped GaN multi-quantum barrier layer is a single-layer structure or a multi-layer structure doped with Si element, and the doping concentration of Si is 1.2×10 17 / cm 3 ~8.6×10 17 / cm 3 ; The thickness of the third Si-doped GaN multi-quantum barrier layer is 6.5 nm to 13.6 nm.

4. The blue light Micro-LED epitaxial structure according to claim 1, characterized in that: The thickness ratio of the third InGaN multi-quantum well layer to the third Si-doped GaN multi-quantum barrier layer is 1:(2.4~4.5); The thickness ratio of the fourth InGaN multi-quantum well layer to the fourth multi-quantum barrier layer is 1:(2.5-5).

5. The blue light Micro-LED epitaxial structure according to claim 1, characterized in that: In the first period of the fourth light blue light multi-quantum well sublayer, the fourth InGaN multi-quantum well layer in the first period is a non-doped InGaN multi-quantum well layer; in the second period of the fourth light blue light multi-quantum well sublayer, the fourth InGaN multi-quantum well layer in the second period is a Mg-doped InGaN multi-quantum well layer, and the doping concentration of Mg is 3.6×10 18 / cm 3 ~5.2×10 19 / cm 3 .

6. The blue light Micro-LED epitaxial structure according to claim 1, characterized in that: The growth temperature of the first InGaN multi-quantum well layer is T1, the growth temperature of the second InGaN multi-quantum well layer is T2, the growth temperature of the third InGaN multi-quantum well layer is T3, and the growth temperature of the fourth InGaN multi-quantum well layer is T4, T1≥T2≥T3≤T4.

7. A method for preparing an epitaxial structure of a blue light Micro-LED according to any one of claims 1 to 6, characterized in that: include: providing a substrate; growing a buffer layer on the substrate; growing an N-type semiconductor layer on the buffer layer; growing a low-temperature stress release layer on the N-type semiconductor layer; growing a multi-quantum well light-emitting layer on the low-temperature stress release layer; growing an electron blocking layer on the multi-quantum well light-emitting layer; growing a P-type semiconductor layer on the electron blocking layer; The multi-quantum well light-emitting layer includes a first light blue multi-quantum well sublayer, a second light blue multi-quantum well sublayer, a third blue multi-quantum well sublayer and a fourth light blue multi-quantum well sublayer which are stacked and grown in sequence from bottom to top.

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