A red light Micro LED epitaxial structure and a manufacturing method thereof

Abstract

The present application discloses a red light MicroLED epitaxial structure and a manufacturing method thereof. The epitaxial structure includes: a substrate, and a buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer sequentially deposited on one surface of the substrate; wherein, the multi-quantum well structure is composed of a plurality of blue light wells, green light wells, and red light wells, and between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth mode with a gradually changing In composition, and at the initial stage of the growth of the red light well, a pulsed Al supply method is introduced. Through the early 3D growth, pre-stress is preset to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor optoelectronic technologies, and in particular, to a red Micro LED epitaxial structure and a manufacturing method thereof. Background Art

[0002] In recent years, III-V nitrides have received great attention in the electrical and optical fields due to their excellent physical and chemical properties, such as large bandgap, high breakdown electric field, high electron saturation mobility, etc. For example, Mini / Micro LEDs that have attracted much attention in the current market, VR, AR, wearable devices, smartphones, etc. are highly favored for their broad application prospects. However, in practical applications, due to limitations in materials, structures, and processes, there are still many problems in the large-scale application of Mini / Micro LEDs. Generally speaking, Micro LEDs require three-color combinations, blue, green, and red (RGB). Currently, the urgent problem to be solved is the development of a red Micro LED epitaxial structure at a small size. In commercial applications, AlInGaP is generally used for the development of red LED structures. However, as the chip size continues to decrease, the efficiency of AlInGaP-based red LEDs drops severely. And due to its smaller carrier diffusion coefficient, smaller surface recombination rate, and extremely strong carrier localization, InGaN has a higher luminous efficiency and lower efficiency droop than AlInGaP at a small size.

[0003] However, in the prior art, when growing InGaN-based red Micro LEDs, due to the imbalance of electron-hole injection and low hole injection efficiency, the luminous efficiency is affected. Other problems, including stress accumulation, strong polarization electric field, etc., are also urgent problems to be solved for current InGaN-based red Micro LEDs. Summary of the Invention

[0004] In view of this, the present invention provides a red Micro LED epitaxial structure and a manufacturing method thereof. By introducing a pulsed Al supply method at the initial stage of the growth of the red well, through 3D growth in the early stage, presetting stress, and increasing the incorporation of In, the growth temperature of the red well is increased, and the crystal quality of the red well is improved.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A red Micro LED epitaxial structure, the red Micro LED epitaxial structure comprising:

[0007] A substrate, and a buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer sequentially deposited on one surface of the substrate;

[0008] Among them, the multi-quantum well structure is composed of multiple blue light wells, green light wells and red light wells. Between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth mode with a gradually changing In composition. At the initial stage of the growth of the red light well, a pulsed Al passing method is introduced. Through the previous 3D growth, prestress is preset to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well.

[0009] Preferably, in the above-mentioned red light Micro LED epitaxial structure, the current spreading layer includes multiple alternately grown U-AlGaN layers and N-GaN layers, and the growth period is 10-20 cycles;

[0010] The thickness of the U-AlGaN layer is 10-20 nm;

[0011] The thickness of the N-GaN layer is 5-10 nm, and the doping Si concentration is 5-10 x10 18 cm -3 。

[0012] Preferably, in the above-mentioned red light Micro LED epitaxial structure, the blue light well includes multiple alternately grown first quantum barrier layers and first quantum well layers, and the growth period is N, where N is 2-4 cycles;

[0013] The bandgap of the blue light well is 2.5-2.8 eV.

[0014] Preferably, in the above-mentioned red light Micro LED epitaxial structure, the first quantum barrier layer is a GaN-Al x Ga 1- x N-GaN layer, and the first quantum well layer is an InGaN layer;

[0015] The thickness of the first quantum barrier layer is 15-20 nm, and the thickness of the first quantum well layer is 2-4 nm.

[0016] Preferably, in the above-mentioned red light Micro LED epitaxial structure, the green light well includes multiple alternately grown second quantum barrier layers and second quantum well layers, and the growth period is N, where N is 2-4 cycles;

[0017] The bandgap of the green light well is 2.1-2.5 eV.

[0018] Preferably, in the above-mentioned red light Micro LED epitaxial structure, the second quantum barrier layer is a GaN-Al x Ga 1- x N-GaN layer, and the second quantum well layer is an InGaN layer;

[0019] The thickness of the second quantum barrier layer is 15 - 20 nm, and the thickness of the second quantum well layer is 2 - 4 nm.

[0020] Preferably, in the above-mentioned red Micro LED epitaxial structure, during the initial growth stage of the red light well, a pulsed Al supply growth method is adopted, and the red light well is an AlInGaN + InGaN layer;

[0021] The bandgap of the red light well is 1.6 - 2.0 eV.

[0022] Preferably, in the above-mentioned red Micro LED epitaxial structure, the hole injection layer includes multiple alternately grown P-InGaN layers and U-GaN layers, with a growth period of 5 - 15 cycles, and the thickness of each cycle is 5 - 10 nm;

[0023] The Mg doping concentration of the P-InGaN layer is 1 - 5x10 18 cm -3 .

[0024] Preferably, in the above-mentioned red Micro LED epitaxial structure, it further includes:

[0025] An undoped AlN low-temperature nucleation layer disposed between the substrate and the buffer layer;

[0026] A P electrode disposed on the surface of the contact layer facing away from the P-GaN layer;

[0027] An N electrode disposed on the surface of the current spreading layer facing away from the buffer layer.

[0028] An embodiment of the present invention further provides a method for manufacturing a red Micro LED epitaxial structure, and the manufacturing method includes:

[0029] Providing a substrate;

[0030] Sequentially depositing a buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer on one surface of the substrate;

[0031] Among them, the multi-quantum well structure is composed of multiple blue light wells, green light wells, and red light wells. Between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth method with a gradually changing In composition, and during the initial growth stage of the red light well, a pulsed Al supply method is introduced. Through 3D growth in the early stage, pre-stress is preset to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well.

[0032] As can be seen from the above description, in the red Micro LED epitaxial structure and its manufacturing method provided by the technical solution of the present invention, a buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer are sequentially deposited on a substrate; wherein, the multi-quantum well structure is composed of a plurality of blue light wells, green light wells, and red light wells, and between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth mode with a gradually changing In composition. At the initial stage of the growth of the red light well, a pulsed Al supply method is introduced. Through the initial 3D growth, prestress is preset to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0034] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions that can be implemented in the present application. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present application.

[0035] Figure 1 Schematic diagram of a red Micro LED epitaxial structure provided by an embodiment of the present invention;

[0036] Figure 2 Conduction band schematic diagram of the MQW-P layer provided by an embodiment of the present invention;

[0037] Figure 3 Schematic diagram of the source supply for the growth of a red light well provided by an embodiment of the present invention;

[0038] Figures 4 - 12 Process flow chart of a manufacturing method of a red Micro LED epitaxial structure provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In the following, embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without making creative efforts belong to the scope of protection of the present application.

[0040] In the prior art, the development of red LED structures is generally based on AlInGaP. However, as the chip size continues to decrease, the efficiency of AlInGaP-based red LEDs drops severely. Due to its smaller carrier diffusion coefficient, smaller surface recombination rate, and extremely strong carrier localization, InGaN has a higher luminous efficiency and lower efficiency droop at small sizes compared to AlInGaP.

[0041] However, there are the following problems in growing InGaN-based red Micro LEDs: 1. High In composition InGaN is required for red light, and high In requires low temperature, which will deteriorate the crystal quality of the material. Therefore, how to improve the crystal quality of high In composition InGaN becomes the key. 2. The injection of electrons and holes is unbalanced, and the hole injection efficiency is low, affecting the luminous efficiency. Other issues, including stress accumulation and strong polarization electric fields, are also problems that need to be urgently solved for InGaN-based red Micro LEDs.

[0042] Currently, the existing ones mainly grow red LEDs based on AlInGaP. Due to its larger carrier diffusion length and surface recombination rate, the luminous efficiency is low at small sizes, and the efficiency droop is also severe.

[0043] In view of this, the present invention provides a red Micro LED epitaxial structure and a manufacturing method thereof. A buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer are sequentially deposited on a substrate. Among them, the multi-quantum well structure is composed of a plurality of blue light wells, green light wells, and red light wells. Between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth mode with a gradually changing In composition. At the initial stage of the growth of the red light well, a pulsed Al supply method is introduced. Through 3D growth in the early stage, stress is pre-set to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well.

[0044] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] In the present invention, the equipment used is MOCVD (Metal Organic Chemical Vapor Deposition). Trimethylgallium (TMGa) / Triethylgallium (TEGa), Trimethylaluminum (TMAl), and ammonia (NH3) are used as the Ga source, Al source, and nitrogen source respectively, N2 is used as the carrier gas, and the N-type doping source and P-type doping source are silane (SiH4) and bis(cyclopentadienyl)magnesium (CP2Mg) respectively.

[0046] Reference Figure 1 and Figure 2 , Figure 1 FIG. is a schematic diagram of a red Micro LED epitaxial structure provided by an embodiment of the present invention. Figure 2 FIG. is a conduction band schematic diagram of the MQW-P layer provided by an embodiment of the present invention.

[0047] As Figure 1 and Figure 2 shown, the red Micro LED epitaxial structure includes:

[0048] a substrate 10, and a buffer layer 12, a current spreading layer 13, a multi-quantum well structure 15 (MQW), an LQB layer 17, a hole injection layer 18, a P-GaN layer 19, and a contact layer 20 sequentially deposited on one side surface of the substrate 10;

[0049] Among them, the multi-quantum well structure 15 is composed of a plurality of blue light wells 151 (QW1), green light wells 152 (QW2), and red light wells 153 (QW3). Between the current spreading layer 13 and the hole injection layer 18, the multi-quantum well structure 15 adopts a growth method with a gradually changing In composition. At the initial stage of the growth of the red light well 153, a pulsed Al supply method is introduced. Through the early 3D growth, prestress is preset to increase the incorporation of In, thereby increasing the growth temperature of the red light well 153 and improving the crystal quality of the red light well 153.

[0050] Among them, the buffer layer 12 is an undoped GaN layer with a thickness of 2.0 um to 2.5 um, such as 2.2 um.

[0051] Among them, the current spreading layer 13 includes multiple alternatingly grown U-AlGaN layers 131 and N-GaN layers 132, and the growth period is 10 - 20 cycles; the thickness of the U-AlGaN layer 131 is 10 - 20 nm, such as 12 nm; the thickness of the N-GaN layer 132 is 5 - 10 nm, such as 8 nm, and the doping Si concentration is 5 - 10x10 18 cm -3 .

[0052] Among them, the LQB layer 17 is a GaN LQB layer, and the thickness of the entire LQB layer 17 is 5 - 10 nm, such as 8 nm. The thin GaN LQB layer is conducive to hole tunneling, achieving the purpose of increasing hole injection.

[0053] Among them, the hole injection layer 18 includes multiple alternatingly grown P-InGaN layers and U-GaN layers, with a growth period of 5 - 15 cycles, and the thickness of each cycle is 5 - 10 nm; the Mg doping concentration of the P-InGaN layer is 1 - 5x10 18 cm -3 。

[0054] Among them, the P-GaN layer 19 is P-type doped, with a thickness of 100 nm - 150 nm, such as 120 nm, and a doping concentration of 5 - 10x10 18 cm -3 。

[0055] Among them, the contact layer 20 is a P-type GaN contact layer, with a thickness of 10 nm - 20 nm, such as 15 nm, and a doping concentration of 1 - 5x10 19 cm -3 。

[0056] Based on Figure 1 the red light Micro LED epitaxial structure shown, it further includes:

[0057] An undoped AlN low-temperature nucleation layer 11 disposed between the substrate 10 and the buffer layer 12, and the thickness of the undoped AlN low-temperature nucleation layer 11 is 10 nm - 20 nm, such as 15 nm;

[0058] An Al x Ga 1-x N layer (not shown in the figure) disposed between the quantum well (QW) and the quantum barrier (QB), where x gradually increases, 0 < x < 1;

[0059] A P electrode 21 disposed on the surface of the contact layer 20 facing away from the P-GaN layer 19;

[0060] An N electrode 14 disposed on the surface of the current spreading layer 13 facing away from the buffer layer 12.

[0061] In the embodiment of the present invention, the multi-quantum well structure 15 is composed of a plurality of blue light wells 151, green light wells 152 and red light wells 153. The blue light wells 151, green light wells 152 and red light wells 153 are sequentially deposited on the surface of the current spreading layer 13 facing away from the buffer layer 12, and the last layer of quantum wells is the blue light well 151. In one period of the multi-quantum well structure 15, the period of the blue light well 151 is N, the period of the green light well 152 is N, and the period of the red light well 153 is 1 or 2.

[0062] Among them, the blue light well 151 includes multiple layers of alternately grown first quantum barrier layers and first quantum well layers, and the growth period is N, where N is 2-4 periods; the first quantum barrier layer is a GaN-Al x Ga 1-x N-GaN layer, and the first quantum well layer is an InGaN layer; the thickness of the first quantum barrier layer can be 15-20 nm, such as 18 nm, and the thickness of the first quantum well layer is 2-4 nm, such as 3 nm; the bandgap of the blue light well 151 is 2.5-2.8 eV.

[0063] Among them, the green light well 152 includes multiple layers of alternately grown second quantum barrier layers and second quantum well layers, and the growth period is N, where N is 2-4 periods; the second quantum barrier layer is a GaN-Al x Ga 1-x N-GaN layer, and the second quantum well layer is an InGaN layer; the thickness of the second quantum barrier layer is 15-20 nm, such as 18 nm, and the thickness of the second quantum well layer is 2-4 nm, such as 3 nm; the bandgap of the green light well 152 is 2.1-2.5 eV.

[0064] Among them, the red light well 153 adopts a growth method of pulsed Al injection, the pulse interval is t0, and the growth time is 5-10 s; the red light well 153 is an AlInGaN+InGaN layer; the bandgap of the red light well 153 is 1.6-2.0 eV. In the present invention, by injecting Al at the initial stage of growth, the purpose of 3D growth in the early stage is achieved, and by presetting stress to enhance the incorporation of In, the growth temperature of the red light well is increased, and the crystal quality of the red light well is improved. The bandgap of the red light well is 1.6-2.0 eV, and the In composition in the InGaN of the red light well 153 is greater than the In composition of the green light well 152.

[0065] In the embodiment of the present invention, the entire multi-quantum well structure 15 (MQW) is designed in a In-graded manner, i.e., a blue light well 151 + a green light well 152 + a red light well 153. The main light emission is from the red light well 153. On the one hand, it is in a In-graded form, where In adopts a gradually transitional way, reducing the large lattice mismatch generated by directly growing InGaN with a high In composition on GaN. At the same time, to adapt to the red light LED in small sizes, a few-period quantum well is adopted, which is beneficial to the peak efficiency shifting towards a small current.

[0066] Moreover, in the initial stage of growth, a pulsed Al supply method is introduced. Through the initial 3D growth, a preset stress is achieved, enhancing the effect of In incorporation. Thus, when reaching the same wavelength, the growth temperature of the red light well 153 can be increased to improve the crystal quality and increase the NH3 cracking efficiency, etc.

[0067] From the above description, it can be seen that in the red light Micro LED epitaxial structure provided by the technical solution of the present invention, a graded In composition form is adopted, with In gradually increasing. Compared with directly growing InGaN with a high In composition on GaN, the graded In composition reduces the lattice mismatch between materials. At the same time, the smaller number of red light wells makes the peak efficiency shift towards a small current, meeting the improvement of the light emission power of the Micro LED under a small current. The pulsed Al treatment in the initial stage of the red light well growth, through presetting stress, increases the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the material. The Al x Ga 1-x N layer improves the light emission power by reducing the accumulated stress and increasing the overlap of the electron-hole wave functions. The relatively thin LQB layer and the P-InGaN / U-GaN hole injection layer increase the hole concentration, which is beneficial to hole injection.

[0068] Based on the above embodiment, another embodiment of the present invention further provides a manufacturing method of a red light Micro LED epitaxial structure, as Figures 1 - 12 shown, Figure 3 which is a schematic diagram of the source supply for the growth of a red light well provided by the embodiment of the present invention, Figures 4 - 12 and is a process flow chart of the manufacturing method of a red light Micro LED epitaxial structure provided by the embodiment of the present invention.

[0069] As Figures 1 - 12 shown, the manufacturing method includes:

[0070] Step S11: As Figure 4 shown, provide a substrate 10, and the substrate 10 can be a sapphire substrate;

[0071] Step S12: As Figures 5 - 12As shown, an undoped AlN low-temperature nucleation layer 11, a buffer layer 12, a current spreading layer 13, a multi-quantum well structure 15, an LQB layer 17, a hole injection layer 18, a P-GaN layer 19, a contact layer 20, and a P electrode 21 and an N electrode 14 are sequentially deposited on one side surface of the substrate 10;

[0072] Among them, the multi-quantum well structure 15 is composed of a plurality of blue light wells 151, green light wells 152, and red light wells 153. And between the current spreading layer 13 and the hole injection layer 18, the multi-quantum well structure 15 adopts a growth mode with a gradually changing In composition. And at the initial stage of the growth of the red light well 153, a pulsed Al supply method is introduced. Through the early 3D growth, pre-stress is preset to increase the incorporation of In, thereby increasing the growth temperature of the red light well 153 and improving the crystal quality of the red light well 153.

[0073] In step S12, first as Figure 5 shown, the sapphire substrate is placed in the MOCVD reaction chamber, the temperature is set to 1100 °C, high-purity hydrogen H is introduced for 5 - 10 min, then the temperature is lowered to 950 °C - 970 °C, and finally an Al source and an N source are introduced to grow an undoped AlN low-temperature nucleation layer 11 with a thickness of 10 nm on the sapphire substrate.

[0074] Furthermore, as Figure 6 shown, after growing the undoped AlN low-temperature nucleation layer 11, the temperature can be further raised to 1050 °C - 1100 °C, then the Al source is turned off, and a TMGa source is introduced to grow a buffer layer 12 with a thickness of 2.0 um - 2.5 um on the side surface of the undoped AlN low-temperature nucleation layer 11 facing away from the sapphire substrate. The buffer layer 12 is an undoped GaN layer, and the purpose is to reduce the lattice mismatch between the sapphire substrate and the subsequent grown materials by growing a high-quality GaN layer.

[0075] Furthermore, as Figure 7 shown, after growing the buffer layer 12, the Al source can be continuously introduced, the temperature is 980 - 1020 degrees, and a U-AlGaN layer 131 with a thickness of 10 - 20 nm (such as 8 nm) is grown on the side surface of the buffer layer 12 facing away from the undoped AlN low-temperature nucleation layer 11; then the Al source is turned off, and silane is introduced to grow a Si-doped N-GaN layer 132 with a thickness of 5 - 10 nm (such as 6 nm) on the side surface of the U-AlGaN layer 131 facing away from the buffer layer 12, and the doping concentration is 5 - 10x10 18 cm -3Among them, the U-AlGaN layer 131 and the N-GaN layer 132 are alternately grown to form a current spreading layer 13 with 10 to 20 periods. The current spreading layer 13 can further block dislocations by using the SL structure to improve the crystal quality, and at the same time use intermittent doping (i.e., doped / undoped / doped / undoped state) to further enhance the current spreading ability.

[0076] Furthermore, as Figure 3 and Figure 8 shown, a multi-quantum well structure 15 is grown on the surface of the current spreading layer 13 facing away from the buffer layer 12; the multi-quantum well structure 15 has a plurality of blue light wells 151, green light wells 152, and red light wells 153. The blue light wells 151, green light wells 152, and red light wells 153 are sequentially deposited on the surface of the current spreading layer 13 facing away from the buffer layer 12, and the last quantum well is still the blue light well 151.

[0077] The blue light well 151 includes multiple alternately grown first quantum barrier layers and first quantum well layers, with a growth period of N, where N is 2 to 4 periods; the green light well 152 includes multiple alternately grown second quantum barrier layers and second quantum well layers, with a growth period of N, where N is 2 to 4 periods; the red light well 153 is an AlInGaN + InGaN layer, with a growth period of 1 or 2.

[0078] In an embodiment of the present invention, taking one period of the multi-quantum well structure 15 as an example, its specific growth process includes:

[0079] 1. Introduce a Ga source, and grow a first quantum barrier layer with a thickness of 15 - 20 nm on the surface of the current spreading layer 13 facing away from the buffer layer 12, that is, a GaN-Al x Ga 1-x N-GaN quantum barrier layer; then introduce an In source, and grow a first quantum well layer with a thickness of 2 - 4 nm on the surface of the GaN-Al x Ga 1- x N-GaN quantum barrier layer facing away from the current spreading layer 13, that is, an InGaN quantum well layer; repeat the above cycle, with the cycle N being 2 - 4, for example, N = 2, to form the blue light well 151, and the bandgap of the blue light well 151 is 2.5 - 2.8 eV.

[0080] 2. Continue to introduce a Ga source, and grow a second quantum barrier layer with a thickness of 15 - 20 nm on the surface of the blue light well 151 facing away from the current spreading layer 13, that is, a GaN-Al x Ga 1-x N-GaN quantum barrier layer; then introduce an In source, and grow a second quantum well layer with a thickness of 2 - 4 nm on the surface of the GaN-Al x Ga 1- xOn the side surface of the N-GaN quantum barrier layer facing away from the blue light well 151, a second quantum well layer with a thickness of 2-4 nm is grown, namely an InGaN quantum well layer; repeating the above cycle, where N is 2-4, for example N = 2, forms a green light well 152. The bandgap of the green light well 152 is 2.1-2.5 eV, and the In composition of the green light well 152 is greater than that of the blue light well 151.

[0081] 3. By means of pulsed Al supply at the initial stage of growth, a thin AlInGaN layer is grown on the side surface of the green light well 152 facing away from the blue light well 151. Then, the Al source is turned off, and an InGaN layer is grown on the AlInGaN layer. The red light well 153 is formed by the previous AlInGaN layer + the subsequent InGaN layer. The pulse interval is t0, and the growth time is 5-10 s. Through Al injection at the initial stage of growth, the purpose of 3D growth in the early stage is achieved. By presetting stress to enhance the incorporation of In, the growth temperature of the quantum well is increased, and the crystal quality of the red light well is improved. The bandgap of the red light well is 1.6-2.0 eV, the growth cycle is 1 or 2, and the In composition of InGaN in the red light well 153 is greater than that of the green light well 152.

[0082] 4. Continue to supply the Ga source, and grow a third quantum barrier layer with a thickness of 15-20 nm on the side surface of the red light well 153 facing away from the green light well 152, namely a GaN-Al x Ga 1-x N-GaN quantum barrier layer; then continue to supply the In source, and grow a third quantum well layer with a thickness of 2-4 nm on the side surface of the GaN-Al x Ga 1-x N-GaN quantum barrier layer facing away from the red light well 153, namely an InGaN quantum well layer. The third quantum barrier layer and the third quantum well layer form the last blue light well 151 (LQW). The bandgap of the blue light well 151 is 2.5-2.8 eV. The purpose is to reduce the damage to the red light well caused by the subsequent temperature rise of the P layer. At the same time, considering the better demand for hole injection in device luminescence at small sizes, a thinner blue light well 151 (thin thickness, low potential barrier) is adopted, which is conducive to hole tunneling and increases the purpose of hole injection.

[0083] In the above method, only the case of N = 2 is taken as an example for illustration, and the number of cycles can also be adjusted according to the actual situation in other methods.

[0084] It should be noted that the Al x Ga 1-xThe N layer (not shown in the figure), with x gradually increasing, 0 < x < 1. This is mainly to increase the overlap of electron-hole wave functions while reducing the stress continuously accumulated in the MQW. As the thickness of the MQW and the In composition increase, the stress accumulation increases. By using the Al x Ga 1-x N layer, the stress accumulation can be reduced, the overlap of electron-hole wave functions can be increased, and the luminescence efficiency can be improved.

[0085] Furthermore, as shown in Figure 9 , on the surface of the multi-quantum structure 15 facing away from the current spreading layer 13, a thin LQB layer 17 is grown. The LQB layer 17 is a GaN LQB layer, and the thickness of the entire LQB layer 17 is 5 - 10 nm, such as 8 nm. The thin GaN LQB layer is beneficial for hole tunneling, achieving the purpose of increasing hole injection.

[0086] Furthermore, as shown in Figure 10 , on the surface of the LQB layer 17 facing away from the multi-quantum structure 15, a hole injection layer 18 is grown. The hole injection layer 18 includes multiple layers of alternately grown P-InGaN layers 181 and U-GaN layers 182.

[0087] After growing the LQB layer 17, the temperature can be raised to 800 - 900 degrees, and then the In / Ga source is continuously introduced. First, a P-InGaN layer 181 is grown on the surface of the LQB layer 17 facing away from the multi-quantum structure 15, with a doping concentration of 1 - 5x10 18 cm -3 . Then, the In source is turned off, and an undoped U-GaN layer 182 is grown on the surface of the P-InGaN layer 181 facing away from the LQB layer 17; the above alternate growth is carried out for 5 - 15 cycles, and the thickness of each cycle is 5 - 10 nm.

[0088] In the design of the P-InGaN / U-GaN hole injection layer in this solution, due to the low activation energy of Mg in InGaN, high hole injection is obtained. At the same time, the P-i-P-i alternate growth is beneficial for improving current spreading and anti-static breakdown ability, meeting the requirements of small-size red LEDs for hole injection and reliability.

[0089] Furthermore, as shown in Figure 11 , the temperature is continuously adjusted to 900 - 1000 °C, and TMGa source, nitrogen source, and bis(cyclopentadienyl)magnesium are introduced. On the surface of the hole injection layer 18 facing away from the LQB layer 17, a P-GaN layer 19 is grown, with a thickness that can be 100 - 150 nm and a doping concentration of 5 - 10x10 18 cm -3 .

[0090] Furthermore, as shown inFigure 12 As shown, a thin p-type GaN contact layer 20 is grown on one side surface of the P-GaN layer 19 facing away from the hole injection layer 18. The thickness can be 10 - 20 nm, and the doping concentration is 1 - 5×10 19 cm -3 , and annealing at 850 - 900 °C for 20 - 30 minutes is required in an N2 atmosphere.

[0091] Finally, as Figure 1 shown, a P electrode 21 is grown on one side surface of the contact layer 20 facing away from the P-GaN layer 19, and an N electrode 14 is grown on one side surface of the current spreading layer 13 facing away from the buffer layer 12.

[0092] It should be noted that the pressure for the entire reaction growth is 100 - 300 torr.

[0093] In the embodiment of the present invention, the entire multi-quantum well structure 15 (MQW) is designed in an In-graded manner, that is, a blue light well 151 + a green light well 152 + a red light well 153. The main emission is from the red light well 153. On the one hand, it is in an In-graded form, and In adopts a gradual transition method, reducing the large lattice mismatch generated by directly growing InGaN with a high In component on GaN. At the same time, to adapt to the red light LED in small sizes, a small number of quantum wells are used, which is beneficial to the peak efficiency shifting towards a small current.

[0094] Moreover, in the initial stage of growth, a pulsed Al supply method is introduced. Through the 3D growth in the early stage, preset stress is achieved, enhancing the effect of In incorporation. Thus, when reaching the same wavelength, the growth temperature of the red light well can be increased, the crystal quality can be improved, and the NH3 cracking efficiency can be increased, etc.

[0095] From the above description, it can be seen that in the InGaN-based red light Micro LED epitaxial structure and its manufacturing method provided by the technical solution of the present invention, an In-graded component form is adopted, with In gradually increasing. Compared with directly growing InGaN with a high In component on GaN, the In-graded component reduces the lattice mismatch between materials. At the same time, the smaller number of red light wells allows the peak efficiency to shift towards a small current, meeting the improvement of the light emission power of the Micro LED at a small current. The pulsed Al treatment in the initial stage of the red light well growth, through preset stress, increases the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the material. The AlxGa1-xN layer in the quantum barrier increases the light emission power by reducing the accumulated stress and increasing the overlap of the electron-hole wave functions. The relatively thin LQB layer and the P-InGaN / U-GaN hole injection layer increase the hole concentration, facilitating hole injection.

[0096] In this specification, the various embodiments are described in a progressive, or parallel, or a combination of progressive and parallel manners. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the embodiments, reference may be made to each other.

[0097] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that an article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such article or device. Without more limitations, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the article or device including the above elements.

[0098] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A red Micro LED epitaxial structure, characterized in that, Comprising: A substrate, and a buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer sequentially deposited on one surface of the substrate; Wherein, the multi-quantum well structure is composed of a plurality of blue light wells, green light wells, and red light wells, and between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth mode with a gradually changing In composition. And at the initial stage of the growth of the red light well, a pulsed Al supply mode is introduced. Through the early 3D growth, stress is pre-set to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well.

2. The red Micro LED epitaxial structure according to claim 1, wherein The current spreading layer includes multiple alternately grown U-AlGaN layers and N-GaN layers, and the growth period is 10 - 20 cycles; The thickness of the U-AlGaN layer is 10 - 20 nm; The thickness of the N-GaN layer is 5-10 nm, and the doping concentration of Si is 5-10x10 18 cm -3 .

3. The red Micro LED epitaxial structure according to claim 1, characterized in that, The blue light well includes multiple alternately grown first quantum barrier layers and first quantum well layers, and the growth period is N, where N is 2 - 4 cycles; The bandgap of the blue light well is 2.5 - 2.8 eV.

4. The red Micro LED epitaxial structure according to claim 3, wherein, The first quantum barrier layer is a GaN-Al x Ga 1-x N-GaN layer, and the first quantum well layer is an InGaN layer; The thickness of the first quantum barrier layer is 15 - 20 nm, and the thickness of the first quantum well layer is 2 - 4 nm.

5. The red light Micro LED epitaxial structure according to claim 1, characterized in that, The green light well includes multiple alternately grown second quantum barrier layers and second quantum well layers, and the growth period is N, where N is 2 - 4 cycles; The bandgap of the green light well is 2.1 - 2.5 eV.

6. The red light Micro LED epitaxial structure according to claim 5, wherein, The second quantum barrier layer is a GaN - Al x Ga 1-x N - GaN layer, and the second quantum well layer is an InGaN layer; The thickness of the second quantum barrier layer is 15 - 20 nm, and the thickness of the second quantum well layer is 2 - 4 nm.

7. The red Micro LED epitaxial structure according to claim 1, wherein At the initial stage of the growth of the red light well, a growth mode with pulsed Al supply is adopted, and the red light well is an AlInGaN + InGaN layer; The bandgap of the red light well is 1.6 - 2.0 eV.

8. The red Micro LED epitaxial structure according to claim 1, characterized in that The hole injection layer includes multiple alternately grown P-InGaN layers and U-GaN layers, and the growth period is 5 - 15 cycles, and the thickness of each cycle is 5 - 10 nm; The Mg doping concentration of the P-InGaN layer is 1-5x10 18 cm -3 .

9. The red light Micro LED epitaxial structure according to claim 1, characterized in that, Also comprising: An undoped AlN low-temperature nucleation layer disposed between the substrate and the buffer layer; A P electrode disposed on one surface of the contact layer facing away from the P-GaN layer; An N electrode disposed on one surface of the current spreading layer facing away from the buffer layer.

10. A manufacturing method of a red light Micro LED epitaxial structure, characterized in that, The manufacturing method includes: Providing a substrate; Sequentially depositing a buffer layer, a current spreading layer, a multi-quantum well structure, an LQB layer, a hole injection layer, a P-GaN layer, and a contact layer on one surface of the substrate; Wherein, the multi-quantum well structure is composed of a plurality of blue light wells, green light wells, and red light wells, and between the current spreading layer and the hole injection layer, the multi-quantum well structure adopts a growth mode with a gradually changing In composition. And at the initial stage of the growth of the red light well, a pulsed Al supply mode is introduced. Through the early 3D growth, stress is pre-set to increase the incorporation of In, thereby increasing the growth temperature of the red light well and improving the crystal quality of the red light well.

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