Epitaxial structure for Micro-LED, preparation method of epitaxial structure and Micro-LED

Abstract

The invention discloses an epitaxial structure for a Micro-LED, a preparation method of the epitaxial structure and the Micro-LED, and relates to the field of semiconductor photoelectric devices. Wherein the epitaxial structure sequentially comprises a substrate, a buffer layer, a non-doped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer; wherein the hole injection enhancement layer sequentially comprises a first sub-layer, a second sub-layer, a third sub-layer and a fourth sub-layer; the first sub-layer comprises AlN layers and GaN layers which are alternately stacked, the second sub-layer comprises Alx1Ga1-x1N layers and first Mg-doped GaN layers which are alternately stacked, the third sub-layer comprises Alx2Ga1-x2N layers and Mg-doped Iny1Ga1-y1N layers which are alternately stacked, and the fourth sub-layer comprises second Mg-doped GaN layers and Mg-doped Iny2Ga1-y2N layers which are alternately stacked; wherein x1 > = x2, and y1 < = y2. According to the invention, the lighting effect of the Micro-LED can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor optoelectronic devices, and in particular to an epitaxial structure for Micro-LED and a preparation method thereof, and Micro-LED. Background Art

[0002] Micro LED display has nanosecond (ns) level high-speed response performance, stable characteristics of inorganic materials, high light efficiency, high reliability, high color purity and contrast, transparency and other excellent properties, and has broad application prospects. However, there are also some problems in its application. For example, as the chip size decreases, the corresponding current density increases, the device peak EQE decreases, and 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, the luminous efficiency of conventional-sized LEDs at this current density is also relatively small. Specifically, the peak EQE of conventional LEDs is usually between 1 and 4 A / cm 2 The current density range is not concerned with the device efficiency at low current density. For example, electron leakage has not occurred or the proportion is very low at low current density. The electron blocking layer structure in the traditional epitaxial structure not only fails to block electrons, but also blocks 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 research and development of high-efficiency Micro LED devices driven by low working current density. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an epitaxial structure for Micro-LED and a preparation method thereof, which has high luminous efficiency at low current density.

[0004] Another technical problem to be solved by the present invention is to provide a Micro-LED having high luminous efficiency at low current density.

[0005] In order to solve the above problems, the present invention discloses an epitaxial structure for Micro-LED, which comprises a substrate, a buffer layer, a non-doped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer sequentially stacked on the substrate;

[0006] Wherein, the hole injection enhancement layer comprises a first sublayer, a second sublayer, a third sublayer and a fourth sublayer which are sequentially stacked on the multi-quantum well layer;

[0007] The first sublayer includes an AlN layer and a GaN layer stacked alternately, and the second sublayer includes an Al x1 Ga 1-x1N layer and a first Mg-doped GaN layer, the third sublayer comprises an alternately stacked Al x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layer, the fourth sublayer includes a second Mg-doped GaN layer and a Mg-doped In layer alternately stacked y2 Ga 1-y2 N layers;

[0008] Among them, x1≥x2, y1≤y2.

[0009] As an improvement of the above technical solution, the number of periods of the first sub-layer is 1 to 3; and / or

[0010] The thickness of the AlN layer is 0.5 nm to 2.8 nm; and / or

[0011] The thickness of the GaN layer is 0.8 nm to 5.6 nm; and / or

[0012] The number of periods of the second sub-layer is 2 to 5; and / or

[0013] The Al x1 Ga 1-x1 The value range of x1 in the N layer is 0.25 to 0.75, and its thickness is 0.5 nm to 3.6 nm; and / or

[0014] The Mg doping concentration in the first Mg-doped GaN layer is 1.2×10 18 cm -3 ~5.8×10 18 cm -3 , and its thickness is 0.5nm~3.6nm.

[0015] As an improvement of the above technical solution, the number of periods of the third sub-layer is 2 to 6; and / or

[0016] The Al x2 Ga 1-x2 The value range of x2 in the N layer is 0.05 to 0.5, and its thickness is 0.5 nm to 4 nm; and / or

[0017] The Mg doped with In y1 Ga 1-y1 The value range of y1 in the N layer is 0.02~0.09, and its Mg doping concentration is 3.6×10 18 cm -3 ~2.5×10 19 cm -3 , with a thickness of 0.2nm to 4nm; and / or

[0018] The period number of the fourth sublayer is 3 to 10; and / or

[0019] The Mg doping concentration in the second Mg-doped GaN layer is 2.5×10 18 cm -3 ~8.6×10 18 cm -3 , having a thickness of 0.5 nm to 3.6 nm; and / or

[0020] The Mg doped with In y2 Ga 1-y2 The value range of y2 in the N layer is 0.03~0.15, and its Mg doping concentration is 1.2×10 19 cm -3 ~5.7×10 19 cm -3 , thickness is 0.5nm~5nm.

[0021] As an improvement of the above technical solution, the number of periods of the first sublayer is less than or equal to the number of periods of the second sublayer, the number of periods of the second sublayer is less than or equal to the number of periods of the third sublayer, and the number of periods of the third sublayer is less than or equal to the number of periods of the fourth sublayer.

[0022] As an improvement of the above technical solution, y1<y2, and the Mg doped with In y1 Ga 1-y1 The Mg doping concentration in the N layer is less than that in the Mg doped In y2 Ga 1-y2 Mg doping concentration in the N layer.

[0023] As an improvement of the above technical solution, x1>x2, and the Mg doping concentration in the first Mg-doped GaN layer is less than that in the Mg-doped In layer. y1 Ga 1-y1 Mg doping concentration in the N layer.

[0024] Correspondingly, the present invention also discloses a method for preparing an epitaxial structure for Micro-LED, which is used to prepare the above-mentioned epitaxial structure for Micro-LED, and comprises:

[0025] Providing a substrate, and sequentially growing a buffer layer, a non-doped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer on the substrate;

[0026] Wherein, the hole injection enhancement layer comprises a first sublayer, a second sublayer, a third sublayer and a fourth sublayer which are sequentially stacked on the multi-quantum well layer;

[0027] The first sublayer includes an AlN layer and a GaN layer stacked alternately, and the second sublayer includes an Al x1 Ga 1-x1N layer and a first Mg-doped GaN layer, the third sublayer comprises an alternately stacked Al x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layer, the fourth sublayer includes a second Mg-doped GaN layer and a Mg-doped In layer alternately stacked y2 Ga 1-y2 N layers;

[0028] Among them, x1≥x2, y1≤y2.

[0029] As an improvement of the above technical solution, the growth temperature of the AlN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or

[0030] The growth temperature of the GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or

[0031] The Al x1 Ga 1-x1 The growth temperature of the N layer is 1000° C. to 1200° C., and the growth pressure is 50 torr to 500 torr; and / or

[0032] The growth temperature of the first Mg-doped GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or

[0033] The Al x2 Ga 1-x2 The growth temperature of the N layer is 950° C. to 1100° C. and the growth pressure is 50 torr to 500 torr; and / or

[0034] The Mg doped with In y1 Ga 1-y1 The growth temperature of the N layer is 800° C. to 950° C. and the growth pressure is 50 torr to 400 torr; and / or

[0035] The growth temperature of the second Mg-doped GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or

[0036] The Mg doped with In y2 Ga 1-y2 The growth temperature of the N layer is 780° C. to 950° C., and the growth pressure is 50 torr to 400 torr.

[0037] As an improvement of the above technical solution, the Ga source used in the growth process of the first sub-layer and the second sub-layer is TMGa; and / or

[0038] The Ga source used in the growth process of the third sublayer and the fourth sublayer is TEGa.

[0039] Correspondingly, the present invention also discloses a Micro-LED, which includes the above-mentioned epitaxial structure for Micro-LED.

[0040] The implementation of the present invention has the following beneficial effects:

[0041] The epitaxial structure for Micro-LED in one embodiment of the present invention introduces a hole injection enhancement layer between the P-type GaN layer and the multi-quantum well layer, which includes a first sublayer, a second sublayer, a third sublayer and a fourth sublayer in sequence; the first sublayer includes an AlN layer and a GaN layer stacked alternately, and the second sublayer includes an Al x1 Ga 1-x1 N layer and the first Mg-doped GaN layer, the third sublayer includes an alternately stacked Al x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layer, the fourth sublayer includes a second Mg-doped GaN layer and a Mg-doped In layer alternately stacked y2 Ga 1-y2 N layer; the hole injection enhancement layer in this embodiment not only effectively blocks electrons, but also improves the injection concentration and injection rate of holes, improves the matching degree of electrons and holes in the multi-quantum well layer, and improves the luminous efficiency of Micro-LED at low current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic structural diagram of an epitaxial structure for Micro-LED in one embodiment of the present invention;

[0043] Figure 2 It is a flow chart of a method for preparing an epitaxial structure for Micro-LED in one embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in further detail below.

[0045] refer to Figure 1An embodiment of the present invention discloses an epitaxial structure for Micro-LED, which includes a substrate 100, a buffer layer 200, a non-doped GaN layer 300, an N-type GaN layer 400, a multi-quantum well layer 500, a hole injection enhancement layer 600, and a P-type GaN layer 700, which are sequentially stacked on the substrate 100. The hole injection enhancement layer 600 includes a first sublayer 610, a second sublayer 620, a third sublayer 630, and a fourth sublayer 640 sequentially stacked on the multi-quantum well layer 500; the first sublayer 610 includes an AlN layer 611 and a GaN layer 612 alternately stacked, and the second sublayer 620 includes an AlN layer 611 and a GaN layer 612 alternately stacked. x1 Ga 1-x1 N layer 621 and the first Mg-doped GaN layer 622, the third sublayer 630 includes an alternately stacked Al x2 Ga 1-x2 N layer 631 and Mg doped In y1 Ga 1-y1 The fourth sublayer 640 includes a second Mg-doped GaN layer 641 and a Mg-doped In layer 642 that are alternately stacked. y2 Ga 1-y2 In this embodiment, the first sublayer 610 is composed of an AlN layer 611 and a GaN layer 612 with a high potential barrier, which can reduce the mobility of electron carriers and prevent electrons from being injected into the P-type GaN layer 700. x1 Ga 1-x1 The N layer 621 has a high potential barrier and can also reduce electron overflow. The first Mg-doped GaN layer 622 introduces Mg doping, which can provide some holes. x1 Ga 1-x1 The heterojunction formed by the N layer 621 can accelerate hole transport and improve the efficiency of hole injection into the multi-quantum well layer 500. x2 Ga 1-x2 The potential barrier of the N layer 631 is high, which can further prevent the electron overflow. y1 Ga 1-y1 N layer 632 can optimize Mg doping with In y1 Ga 1-y1 The N layer 632 stores holes and increases the hole concentration. y2 Ga 1-y2The N layer 642 can provide holes, optimize the matching degree of electrons and holes in the multi-quantum well layer 500, and improve the light efficiency at low current density; secondly, it can store holes to improve the light efficiency; thirdly, the heterojunction formed by it can form a hole accelerator to increase the injection speed of holes. In summary, the hole injection enhancement layer 600 in this embodiment not only effectively blocks electrons, but also improves the injection concentration and injection rate of holes, improves the matching degree of electrons and holes in the multi-quantum well layer 500, and improves the light efficiency of Micro-LED at low current density.

[0046] The period number of the first sublayer 610 is 1 to 5. If the period number is too large, the blocking effect on hole carriers is too strong, and it is difficult to effectively improve the light efficiency under low current density. Exemplarily, the period number of the first sublayer 610 is 2, 3 or 4, but not limited thereto. Preferably, it is 1 to 3.

[0047] The thickness of the AlN layer 611 is 0.5 nm to 5 nm, and is exemplarily 0.8 nm, 1.2 nm, 1.6 nm, 2 nm, 3 nm, 4 nm or 4.5 nm, but is not limited thereto, and is preferably 0.5 nm to 2.8 nm.

[0048] The thickness of the GaN layer 612 is 0.5 nm to 8 nm, exemplarily 0.8 nm, 1.4 nm, 3 nm, 5 nm, 7 nm or 7.5 nm, but not limited thereto, preferably 0.8 nm to 5.6 nm.

[0049] The number of periods of the second sub-layer 620 is 1 to 8, exemplarily 2, 4, 6 or 7, but not limited thereto, and preferably 2 to 5.

[0050] Among them, Al x1 Ga 1-x1 The proportion of Al components in the N layer 621 (i.e., x1) is 0.2 to 0.75. If x1>0.75, the blocking effect on hole carriers is too strong, and it is difficult to effectively improve the light efficiency at a small current density. If x1<0.2, the polarization electric field intensity generated by the first Mg-doped GaN layer 622 is weak, and it is difficult to effectively accelerate hole transport. Exemplarily, x1 is 0.22, 0.3, 0.38, 0.46, 0.5, 0.6 or 0.73, but not limited to this. Preferably, the value range of x1 is 0.25 to 0.75. Al x1 Ga 1-x1 The thickness of the N layer 621 is 0.5 nm to 5 nm, and is exemplarily 0.7 nm, 1.3 nm, 2.5 nm, 3 nm, 4 nm or 4.4 nm, but is not limited thereto, and is preferably 0.5 nm to 3.6 nm.

[0051] The Mg doping concentration in the first Mg-doped GaN layer 622 is 1×10 18 cm -3 ~1×10 19 cm -3 , exemplarily 1.5×10 18 cm -3 , 4×10 18 cm -3 , 6×10 18 cm -3 , 8×10 18 cm -3 or 9×10 18 cm -3 , but not limited thereto. Preferably 1.2×10 18 cm -3 ~5.8×10 18 cm -3 The thickness of the first Mg-doped GaN layer 622 is 0.5 nm to 5 nm, and is exemplarily 0.7 nm, 1.3 nm, 2.5 nm, 3 nm, 4 nm or 4.4 nm, but is not limited thereto, and is preferably 0.5 nm to 3.6 nm.

[0052] The number of periods of the third sub-layer 630 is 2 to 8, exemplarily 3, 4, 6 or 7, but not limited thereto, and preferably 2 to 6.

[0053] Among them, Al x2 Ga 1-x2 The proportion of Al component in the N layer 631 (i.e. x2) is 0.05-0.6, and is 0.07, 0.1, 0.2, 0.3, 0.4 or 0.53, but is not limited thereto. Preferably, it is 0.05-0.5. Al x2 Ga 1-x2 The thickness of the N layer 631 is 0.5 nm to 5 nm, and is exemplarily 0.8 nm, 1.4 nm, 2 nm, 3 nm, 4 nm or 4.8 nm, but is not limited thereto, and is preferably 0.5 nm to 4 nm.

[0054] Among them, Mg doped with In y1 Ga 1-y1 The proportion of In component in N layer 632 (i.e., y1) is 0.02-0.1, and its Mg doping concentration is 3×10 18 cm -3 ~5×10 19 cm -3 , exemplarily 5×10 18 cm -3 , 8×10 18 cm -3 , 1×10 19 cm-3 , 3×10 19 cm -3 or 4×10 19 cm -3 , but not limited thereto. Preferably 3.6×10 18 cm -3 ~2.5×10 19 cm -3 Mg doped with In y1 Ga 1-y1 The thickness of the N layer 632 is 0.2 nm to 5 nm, and is exemplarily 0.5 nm, 1.7 nm, 3 nm, 4 nm or 4.5 nm, but is not limited thereto, and is preferably 0.2 nm to 4 nm.

[0055] The number of periods of the fourth sub-layer 640 is 2-10, exemplarily 3, 5 or 7, but not limited thereto, and preferably 3-10.

[0056] The Mg doping concentration in the second Mg-doped GaN layer 641 is 2×10 18 cm -3 ~1×10 19 cm -3 , exemplarily 1.5×10 18 cm -3 , 4×10 18 cm -3 , 6×10 18 cm -3 , 8×10 18 cm -3 or 9×10 18 cm -3 , but not limited thereto. Preferably, it is 2.5×10 18 cm -3 ~8.6×10 18 cm -3 The thickness of the second Mg-doped GaN layer 641 is 0.5 nm to 5 nm, and is exemplarily 0.8 nm, 1.4 nm, 3 nm, 3.8 nm, 4.2 nm or 4.8 nm, but is not limited thereto, and is preferably 0.5 nm to 3.6 nm.

[0057] Among them, Mg doped with In y2 Ga 1-y2 The ratio of In component in N layer 642 (i.e., y2) is 0.03-0.2, and is 0.05, 0.08, 0.1, 0.13 or 0.17, but is not limited thereto. Preferably, it is 0.03-0.15. y2 Ga 1-y2 The Mg doping concentration of the N layer 642 is 1×10 19 cm-3 ~8×10 19 cm -3 , exemplarily 1.5×10 19 cm -3 , 3×10 19 cm -3 , 4.5×10 19 cm -3 , 6×10 19 cm -3 or 7.5×10 19 cm -3 , but not limited thereto. Preferably 1.2×10 19 cm -3 ~5.7×10 19 cm -3 Mg doped with In y2 Ga 1-y2 The thickness of the N layer 642 is 0.5 nm to 6 nm, and is exemplarily 0.8 nm, 1.5 nm, 2.7 nm, 3.4 nm, 4.5 nm or 5.3 nm, but is not limited thereto, and is preferably 0.5 nm to 5 nm.

[0058] The substrate 100 is a sapphire substrate 100 , a silicon substrate 100 or a SiC substrate 100 , but is not limited thereto. A sapphire substrate 100 is preferred.

[0059] The buffer layer 200 may be an AlN layer or an AlGaN layer, but is not limited thereto. Preferably, it is an AlN layer. The buffer layer 200 has a thickness of 30 nm to 80 nm.

[0060] The thickness of the non-doped GaN layer 300 is 1 μm to 5 μm.

[0061] The N-type GaN layer 400 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.

[0062] The multi-quantum well 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 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 components 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.

[0063] The P-type GaN layer 700 is a Mg-doped GaN layer, and its Mg doping concentration is 1×10 19 cm -3 ~1×10 21 cm -3 The thickness of the P-type GaN layer 700 is 150 nm to 300 nm.

[0064] Preferably, in one embodiment, the period number of the first sublayer 610 ≤ the period number of the second sublayer 620 ≤ the period number of the third sublayer 630 ≤ the period number of the fourth sublayer 640. Based on the technical solutions of the above embodiments, the light efficiency at low current density can be further improved.

[0065] Preferably, in one embodiment, y1<y2, and Mg doped with In y1 Ga 1-y1 The Mg doping concentration in the N layer 632 is less than that of Mg doped In y2 Ga 1-y2 Mg doping concentration in the N layer 642. Based on the technical solution of the above embodiment, the storage function of holes can be further optimized, the hole concentration can be increased, and the light efficiency can be improved.

[0066] Preferably, in one embodiment, x1>x2, and the Mg doping concentration in the first Mg-doped GaN layer 622 is less than that in the Mg-doped In layer 624. y1 Ga 1-y1 Mg doping concentration in the N layer 632. Based on the technical solution of the above embodiment, the blocking effect of the hole injection blocking layer on holes can be further reduced, the hole injection rate can be accelerated, and the light efficiency can be improved.

[0067] Accordingly, reference Figure 2 The present invention also discloses a method for preparing an epitaxial structure for Micro-LED, which is used to prepare the above-mentioned epitaxial structure for Micro-LED, and comprises:

[0068] S1: providing a substrate;

[0069] S2: sequentially growing a buffer layer, a non-doped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer on the substrate;

[0070] Specifically, step S2 includes:

[0071] S21: growing a buffer layer on the substrate;

[0072] Specifically, in one embodiment, an AlN layer may be grown by PVD or MOCVD as a buffer layer, but is not limited thereto.

[0073] S22: growing a non-doped GaN layer on the buffer layer;

[0074] Specifically, in one embodiment, the undoped GaN layer is grown by MOCVD, the growth temperature is 1000° C. to 1200° C., and the growth pressure is 100 torr to 500 torr.

[0075] S23: growing an N-type GaN layer on the non-doped GaN layer;

[0076] Specifically, in one embodiment, the N-type GaN layer is grown by MOCVD, the growth temperature is 1000° C. to 1200° C., and the growth pressure is 100 torr to 500 torr.

[0077] S24: growing a multi-quantum well layer on the N-type GaN layer;

[0078] Specifically, in one embodiment, the InGaN quantum well layer and the GaN quantum barrier layer are periodically grown by MOCVD, wherein the growth temperature of the InGaN quantum well layer is 750°C to 850°C, the growth pressure is 50 torr to 500 torr, and the growth temperature of the GaN quantum barrier layer is 850°C to 950°C, and the growth pressure is 50 torr to 500 torr.

[0079] S25: growing a hole injection enhancement layer on the multi-quantum well layer;

[0080] In one embodiment, step S25 includes:

[0081] S251: growing a first sublayer on the multi-quantum well layer;

[0082] Specifically, in one embodiment, an AlN layer and a GaN layer are periodically grown by MOCVD until a first sub-layer is obtained.

[0083] The growth temperature of the AlN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; the growth temperature of the GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr.

[0084] Specifically, during the growth of the GaN layer, the Ga source may be TMGa or TEGa, but is not limited thereto. Preferably, in one embodiment, TMGa is used, which can increase the growth rate of the GaN layer.

[0085] S252: growing a second sub-layer on the first sub-layer;

[0086] Specifically, in one embodiment, Al is periodically grown by MOCVD. x1 Ga 1-x1 N layer and the first Mg-doped GaN layer until the second sub-layer is obtained.

[0087] Among them, Al x1 Ga 1-x1 The growth temperature of the N layer is 1000° C. to 1200° C., and the growth pressure is 50 torr to 500 torr; the growth temperature of the first Mg-doped GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr.

[0088] Specifically, during the growth of the second sub-layer, the Ga source may be TMGa or TEGa, but is not limited thereto. Preferably, in one embodiment, TMGa is used, which can increase the growth rate.

[0089] S253: growing a third sub-layer on the second sub-layer;

[0090] Specifically, in one embodiment, Al is periodically grown by MOCVD. x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layers, until the third sub-layer is obtained.

[0091] Among them, Al x2 Ga 1-x2 The growth temperature of the N layer is 950℃~1100℃, and the growth pressure is 50torr~500torr; Mg doped with In y1 Ga 1-y1 The growth temperature of the N layer is 800° C. to 950° C., and the growth pressure is 50 torr to 400 torr.

[0092] Specifically, during the growth of the third sub-layer, the Ga source may be TMGa or TEGa, but is not limited thereto. Preferably, in one embodiment, TEGa is used, which has a low growth rate but a high crystal quality of the grown film layer.

[0093] S254: growing a fourth sublayer on the third sublayer to obtain a hole injection enhancement layer;

[0094] Specifically, in one embodiment, the second Mg-doped GaN layer and the Mg-doped In layer are periodically grown by MOCVD. y2 Ga 1-y2 N layers, until the fourth sub-layer is obtained.

[0095] The growth temperature of the second Mg-doped GaN layer is 900°C to 1050°C, and the growth pressure is 50 torr to 360 torr; the Mg-doped In y2 Ga 1-y2 The growth temperature of the N layer is 780° C. to 950° C., and the growth pressure is 50 torr to 400 torr.

[0096] Specifically, during the growth of the fourth sublayer, the Ga source may be TMGa or TEGa, but is not limited thereto. Preferably, in one embodiment, TEGa is used, which has a low growth rate but a high crystal quality of the grown film layer.

[0097] S26: growing a P-type GaN layer on the hole injection enhancement layer;

[0098] Specifically, in one embodiment, the P-type GaN layer is grown by MOCVD, the growth temperature is 900° C. to 1000° C., and the growth pressure is 100 torr to 500 torr.

[0099] Correspondingly, an embodiment of the present invention further discloses a Micro-LED, which includes the above-mentioned epitaxial structure for Micro-LED.

[0100] The present invention will be further described below with specific embodiments:

[0101] Example 1

[0102] This embodiment provides an epitaxial structure for Micro-LED, which includes a substrate, a buffer layer, an undoped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer stacked on the substrate in sequence. The substrate is a sapphire substrate, the thickness of the undoped GaN layer is 2 μm, the Si doping concentration of the N-type GaN layer is 8×10 18 cm -3 , with a thickness of 2μm. The multi-quantum well layer is a periodic structure with 10 periods. Each period includes sequentially stacked InGaN quantum well layers and GaN quantum barrier layers. The In component in the InGaN quantum well layer accounts for 0.15, and its thickness is 4nm. The thickness of the GaN quantum barrier layer is 10nm.

[0103] The hole injection enhancement layer includes a first sublayer, a second sublayer, a third sublayer and a fourth sublayer sequentially stacked on the multi-quantum well layer. The first sublayer includes an AlN layer and a GaN layer stacked alternately, the number of cycles is 3, the thickness of the AlN layer is 2nm, and the thickness of the GaN layer is 4nm. The second sublayer includes an AlN layer stacked alternately. x1 Ga 1-x1 N layer and the first Mg-doped GaN layer, the period number is 3, Al x1 Ga 1-x1 The thickness of the N layer (x1 = 0.5) is 3 nm, and the Mg doping concentration in the first Mg-doped GaN layer is 5×10 18 cm -3 , with a thickness of 3 nm. The third sublayer includes alternately stacked Al x2 Ga 1-x2 N layer and Mg doped with Iny1 Ga 1-y1 N layers, the period number is 3, Al x2 Ga 1-x2 The thickness of the N layer (x2 = 0.5) is 2 nm, and the Mg is doped with In y1 Ga 1-y1 The Mg doping concentration in the N layer (y1 = 0.08) is 5×10 18 cm -3 , and its thickness is 2nm. The fourth sublayer includes a second Mg-doped GaN layer and a Mg-doped In layer alternately stacked y2 Ga 1-y2 N layer, the period number is 3, and the Mg doping concentration in the second Mg-doped GaN layer is 8×10 18 cm -3 , its thickness is 2nm, Mg doped with In y2 Ga 1-y2 The Mg doping concentration in the N layer (y2 = 0.08) is 2×10 19 cm -3 .

[0104] Among them, the Mg doping concentration in the P-type GaN layer is 5×10 19 cm -3 , and its thickness is 200nm.

[0105] The method for preparing the epitaxial wafer for Micro-LED in this embodiment includes the following steps:

[0106] (1) providing a substrate;

[0107] (2) growing a buffer layer on the substrate;

[0108] Specifically, an AlN layer is grown by PVD to serve as a buffer layer.

[0109] (3) growing a non-doped GaN layer on the buffer layer;

[0110] Specifically, the non-doped GaN layer is grown by MOCVD, with a growth temperature of 1080° C. and a growth pressure of 300 torr.

[0111] (4) growing an N-type GaN layer on the undoped GaN layer;

[0112] Specifically, the N-type GaN layer is grown by MOCVD, with a growth temperature of 1100° C. and a growth pressure of 300 torr.

[0113] (5) growing a multi-quantum well layer on the N-type GaN layer;

[0114] Specifically, InGaN quantum well layers and GaN quantum barrier layers are periodically grown by MOCVD until a multi-quantum well layer is obtained, wherein the growth temperature of the InGaN quantum well layer is 780°C and the growth pressure is 200 torr, and the growth temperature of the GaN quantum barrier layer is 900°C and the growth pressure is 200 torr.

[0115] (6) growing a first sublayer on the multi-quantum well layer;

[0116] Specifically, AlN layer and GaN layer are periodically grown by MOCVD until the first sublayer is obtained. The growth temperature of the AlN layer is 950°C and the growth pressure is 200 torr; the growth temperature of the GaN layer is 900°C and the growth pressure is 200 torr. The Ga source used in the growth process of the first sublayer is TMGa.

[0117] (7) growing a second sublayer on the first sublayer;

[0118] Specifically, Al is grown periodically by MOCVD. x1 Ga 1-x1 N layer and the first Mg-doped GaN layer until the second sublayer is obtained. x1 Ga 1-x1 The growth temperature of the N layer is 1100° C., and the growth pressure is 200 torr; the growth temperature of the first Mg-doped GaN layer is 950° C., and the growth pressure is 200 torr; wherein, the Ga source used in the growth process of the second sublayer is TMGa.

[0119] (8) growing a third sub-layer on the second sub-layer;

[0120] Specifically, Al is grown periodically by MOCVD. x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layers, until the third sublayer is obtained. x2 Ga 1-x2 The growth temperature of the N layer is 1000℃ and the growth pressure is 200torr; Mg doped with In y1 Ga 1-y1 The growth temperature of the N layer is 920° C. and the growth pressure is 200 torr; wherein the Ga source used in the growth process of the third sublayer is TMGa.

[0121] (8) growing a fourth sublayer on the third sublayer to obtain a hole injection enhancement layer;

[0122] Specifically, the second Mg-doped GaN layer and the Mg-doped In layer are periodically grown by MOCVD. y2 Ga 1-y2N layer until the fourth sublayer is obtained. The growth temperature of the second Mg-doped GaN layer is 1000°C and the growth pressure is 200 torr; the Mg-doped In y2 Ga 1-y2 The growth temperature of the N layer is 880° C. and the growth pressure is 200 torr. The Ga source used in the growth process of the fourth sublayer is TMGa.

[0123] (9) growing a P-type GaN layer on the hole injection enhancement layer;

[0124] Specifically, the P-type GaN layer is grown by MOCVD, with a growth temperature of 950° C. and a growth pressure of 300 torr.

[0125] Example 2

[0126] This embodiment provides an epitaxial structure for Micro-LED, which is different from Embodiment 1 in that:

[0127] The number of periods of the first sublayer is 2, the number of periods of the second sublayer is 4, the number of periods of the third sublayer is 5, and the number of periods of the fourth sublayer is 8.

[0128] The rest are the same as in Example 1.

[0129] Example 3

[0130] This embodiment provides an epitaxial structure for Micro-LED, which differs from Embodiment 2 in that:

[0131] Mg doped with In y1 Ga 1-y1 In the N layer, y1 = 0.03, Mg doped with In y2 Ga 1-y2 In layer N, y2=0.1.

[0132] The rest is the same as Example 2.

[0133] Example 4

[0134] This embodiment provides an epitaxial structure for Micro-LED, which is different from Embodiment 3 in that:

[0135] Al x1 Ga 1-x1 In the N layer, x1 = 0.35, Al x2 Ga 1-x2 In the N layer, x2=0.1, and the Mg doping concentration in the first Mg-doped GaN layer is 1.2×10 18 cm -3 , Mg doped with In y1 Ga 1-y1 The Mg doping concentration in the N layer is 1×1019 cm -3 .

[0136] The rest is the same as Example 3.

[0137] Example 5

[0138] This embodiment provides an epitaxial structure for Micro-LED, which is different from Embodiment 4 in that:

[0139] The Ga source used in the growth process of the third sublayer and the fourth sublayer is TEGa.

[0140] The rest are the same as in Example 4.

[0141] Comparative Example 1

[0142] This comparative example provides an epitaxial structure for Micro-LED, which differs from Example 1 in that:

[0143] An electron blocking layer is provided between the multi-quantum well layer and the P-type GaN layer, which is Al 0.5 Ga 0.5 The N layer has a thickness of 50 nm, a growth temperature of 1100° C., and a growth pressure of 300 torr.

[0144] The rest are the same as in Example 1.

[0145] Comparative Example 2

[0146] This comparative example provides an epitaxial structure for Micro-LED, which differs from Example 1 in that:

[0147] The hole injection enhancement layer is not included, and accordingly the steps for preparing this layer are not included.

[0148] The rest are the same as in Example 1.

[0149] Comparative Example 3

[0150] This comparative example provides an epitaxial structure for Micro-LED, which differs from Example 1 in that:

[0151] The first sub-layer is not included, and accordingly the steps for preparing this layer are not included.

[0152] The rest are the same as in Example 1.

[0153] Comparative Example 4

[0154] This comparative example provides an epitaxial structure for Micro-LED, which differs from Example 1 in that:

[0155] The second sub-layer is not included, and accordingly the steps for preparing this layer are also not included.

[0156] The rest are the same as in Example 1.

[0157] Comparative Example 5

[0158] This comparative example provides an epitaxial structure for Micro-LED, which differs from Example 1 in that:

[0159] The third sub-layer is not included, and accordingly the preparation steps of this layer are not included.

[0160] The rest are the same as in Example 1.

[0161] Comparative Example 6

[0162] This comparative example provides an epitaxial structure for Micro-LED, which differs from Example 1 in that:

[0163] The fourth sub-layer is not included, and accordingly the preparation steps of this layer are not included.

[0164] The rest are the same as in Example 1.

[0165] The epitaxial structures of Examples 1 to 5 and Comparative Examples 1 to 6 were made into Micro-LEDs at a current density of 0.2 A / cm 2 The luminous brightness was tested under the conditions of . The luminous brightness improvement rate was calculated based on the data of comparative example 1. The specific results are shown in the following table:

[0166] Brightness increase rate Example 1 3.17％ Example 2 4.05％ Example 3 5.32％ Example 4 7.41％ Example 5 7.55％ Comparative Example 1 - Comparative Example 2 0.57％ Comparative Example 3 1.58％ Comparative Example 4 1.89％ Comparative Example 5 1.28％ Comparative Example 6 1.13％

[0167] It can be seen from the table that when the hole injection enhancement layer in the embodiment of the present invention is used, the luminous brightness of the Micro-LED at a low current density can be effectively improved.

[0168] The above is a preferred embodiment of the invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the invention. These improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. An epitaxial structure for Micro-LED, characterized in that: It comprises a substrate, a buffer layer, a non-doped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer stacked in sequence on the substrate; Wherein, the hole injection enhancement layer comprises a first sublayer, a second sublayer, a third sublayer and a fourth sublayer which are sequentially stacked on the multi-quantum well layer; The first sublayer includes an AlN layer and a GaN layer stacked alternately, and the second sublayer includes an Al x1 Ga 1- x1 N layer and a first Mg-doped GaN layer, the third sublayer comprises an alternately stacked Al x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layer, the fourth sublayer includes a second Mg-doped GaN layer and a Mg-doped In layer alternately stacked y2 Ga 1-y2 N layers; Among them, x1≥x2, y1≤y2.

2. The epitaxial structure for Micro-LED according to claim 1, characterized in that: The period number of the first sublayer is 1 to 3; and / or The thickness of the AlN layer is 0.5 nm to 2.8 nm; and / or The thickness of the GaN layer is 0.8 nm to 5.6 nm; and / or The number of periods of the second sub-layer is 2 to 5; and / or The Al x1 Ga 1-x1 The value range of x1 in the N layer is 0.25 to 0.75, and its thickness is 0.5 nm to 3.6 nm; and / or The Mg doping concentration in the first Mg-doped GaN layer is 1.2×10 18 cm -3 ~5.8×10 18 cm -3 , and its thickness is 0.5nm~3.6nm.

3. The epitaxial structure for Micro-LED according to claim 1, characterized in that: The period number of the third sub-layer is 2 to 6; and / or The Al x2 Ga 1-x2 The value range of x2 in the N layer is 0.05 to 0.5, and its thickness is 0.5 nm to 4 nm; and / or The Mg doped with In y1 Ga 1-y1 The value range of y1 in the N layer is 0.02~0.09, and its Mg doping concentration is 3.6×10 18 cm -3 ~2.5×10 19 cm -3 , with a thickness of 0.2nm to 4nm; and / or The period number of the fourth sublayer is 3 to 10; and / or The Mg doping concentration in the second Mg-doped GaN layer is 2.5×10 18 cm -3 ~8.6×10 18 cm -3 , having a thickness of 0.5 nm to 3.6 nm; and / or The Mg doped with In y2 Ga 1-y2 The value range of y2 in the N layer is 0.03~0.15, and its Mg doping concentration is 1.2×10 19 cm -3 ~5.7×10 19 cm -3 , thickness is 0.5nm~5nm.

4. The epitaxial structure for Micro-LED according to any one of claims 1 to 3, characterized in that: The number of periods of the first sublayer is less than or equal to the number of periods of the second sublayer, the number of periods of the second sublayer is less than or equal to the number of periods of the third sublayer, and the number of periods of the third sublayer is less than or equal to the number of periods of the fourth sublayer.

5. The epitaxial structure for Micro-LED according to any one of claims 1 to 3, characterized in that: y1<y2, and the Mg is doped with In y1 Ga 1-y1 The Mg doping concentration in the N layer is less than that in the Mg doped In y2 Ga 1-y2 Mg doping concentration in the N layer.

6. The epitaxial structure for Micro-LED according to any one of claims 1 to 3, characterized in that: x1>x2, and the Mg doping concentration in the first Mg doped GaN layer is less than that in the Mg doped In layer. y1 Ga 1-y1 Mg doping concentration in the N layer.

7. A method for preparing an epitaxial structure for Micro-LED, used for preparing the epitaxial structure for Micro-LED according to any one of claims 1 to 6, characterized in that: include: Providing a substrate, and sequentially growing a buffer layer, a non-doped GaN layer, an N-type GaN layer, a multi-quantum well layer, a hole injection enhancement layer and a P-type GaN layer on the substrate; Wherein, the hole injection enhancement layer comprises a first sublayer, a second sublayer, a third sublayer and a fourth sublayer which are sequentially stacked on the multi-quantum well layer; The first sublayer includes an AlN layer and a GaN layer stacked alternately, and the second sublayer includes an Al x1 Ga 1- x1 N layer and a first Mg-doped GaN layer, the third sublayer comprises an alternately stacked Al x2 Ga 1-x2 N layer and Mg doped with In y1 Ga 1-y1 N layer, the fourth sublayer includes a second Mg-doped GaN layer and a Mg-doped In layer alternately stacked y2 Ga 1-y2 N layers; Among them, x1≥x2, y1≤y2.

8. The epitaxial structure for Micro-LED according to claim 7, characterized in that: The AlN layer has a growth temperature of 900° C. to 1050° C. and a growth pressure of 50 torr to 360 torr; and / or The growth temperature of the GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or The Al x1 Ga 1-x1 The growth temperature of the N layer is 1000° C. to 1200° C., and the growth pressure is 50 torr to 500 torr; and / or The growth temperature of the first Mg-doped GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or The Al x2 Ga 1-x2 The growth temperature of the N layer is 950° C. to 1100° C. and the growth pressure is 50 torr to 500 torr; and / or The Mg doped with In y1 Ga 1-y1 The growth temperature of the N layer is 800° C. to 950° C. and the growth pressure is 50 torr to 400 torr; and / or The growth temperature of the second Mg-doped GaN layer is 900° C. to 1050° C., and the growth pressure is 50 torr to 360 torr; and / or The Mg doped with In y2 Ga 1-y2 The growth temperature of the N layer is 780° C. to 950° C., and the growth pressure is 50 torr to 400 torr.

9. The epitaxial structure for Micro-LED according to claim 7, characterized in that: The Ga source used in the growth process of the first sublayer and the second sublayer is TMGa; and / or The Ga source used in the growth process of the third sublayer and the fourth sublayer is TEGa.

10. A Micro-LED, characterized in that: It comprises the epitaxial structure for Micro-LED as claimed in any one of claims 1 to 6.

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