Epitaxial structure and method of fabricating the same

Abstract

This invention discloses an epitaxial structure and its fabrication method. The epitaxial structure includes at least two stacked light-emitting units; each light-emitting unit includes a stacked N-type conductive layer, a light-emitting layer, and a P-type conductive layer; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two sequentially stacked quantum wells, each quantum well including a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, with the second AlGaN layer disposed between the well layer and the barrier layer. This improves the heat resistance of the light-emitting layer, reduces the impact of the subsequent growth process on the initially grown light-emitting units, and improves the quality of the epitaxial structure. When forming a full-color Micro-LED chip, the fabrication process can be simplified while ensuring the quality of the full-color Micro-LED chip, thus reducing the fabrication cost of the full-color Micro-LED chip.

Description

Technical Field

[0001] This invention relates to the field of display technology, and more particularly to an epitaxial structure and its fabrication method. Background Technology

[0002] Micro-LEDs, due to their advantages such as high responsiveness, high brightness, high contrast, ultra-high resolution, and low power consumption, have experienced rapid development in recent years and are hailed as the next generation of display devices.

[0003] Micro-LED chips are typically smaller than 50μm. Currently, the mainstream solutions for achieving full-color Micro-LEDs include mass transfer and vertically stacked pixel solutions. However, these mainstream full-color solutions are highly dependent on equipment precision and process yield. Therefore, in general, the cost of full-color Micro-LED chips remains high, and the processes are complex, severely hindering the development of full-color Micro-LEDs. Summary of the Invention

[0004] This invention provides an epitaxial structure and its fabrication method to reduce the manufacturing cost of color Micro-LED chips.

[0005] In a first aspect, embodiments of the present invention provide an epitaxial structure comprising at least two stacked light-emitting units; each light-emitting unit comprising a stacked N-type conductive layer, a light-emitting layer, and a P-type conductive layer; the light-emitting layer comprising at least one layer unit structure; each layer unit structure comprising at least two sequentially stacked quantum wells, each quantum well comprising a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer.

[0006] Optionally, it further includes a substrate; along the direction from the substrate to the light-emitting unit, the Al composition in the AlGaN layer of the light-emitting unit closer to the substrate is less than the Al composition in the AlGaN layer of the light-emitting unit farther from the substrate.

[0007] Optionally, the light-emitting layer includes at least two of the layer unit structures, and the light-emitting layer further includes a P-type barrier layer; the P-type barrier layer and the layer unit structures are alternately arranged.

[0008] Optionally, the P-type barrier layer includes a p-AlGaN layer or a p-AlGaInN layer.

[0009] Optionally, it further includes at least one tunneling junction insertion layer; the tunneling junction insertion layer is alternately disposed with the light-emitting unit.

[0010] Optionally, the tunneling junction insertion layer includes a first P-type doped layer, a second P-type doped layer, a first N-type doped layer, and a second N-type doped layer stacked sequentially; the band gap of the second P-type doped layer is smaller than the band gap of the first P-type doped layer; and the band gap of the first N-type doped layer is smaller than the band gap of the second N-type doped layer.

[0011] Optionally, the first P-type doped layer and the second N-type doped layer comprise GaN layers, and the second P-type doped layer and the first N-type doped layer comprise InGaN layers; the In content in the InGaN layer is less than 20%.

[0012] In a second aspect, embodiments of the present invention provide a method for fabricating an epitaxial structure, used to fabricate the epitaxial structure described in the first aspect; comprising: An N-type conductive layer of the first light-emitting unit is grown on the substrate; A light-emitting layer is grown on the N-type conductive layer of the first light-emitting unit; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer; A P-type conductive layer is grown on the light-emitting layer of the first light-emitting unit; An N-type conductive layer for the next light-emitting unit is grown on the side of the P-type conductive layer of the previous light-emitting unit that is away from the substrate. A light-emitting layer is grown on the N-type conductive layer of the next light-emitting unit; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer; A P-type conductive layer is grown on the light-emitting layer of the next light-emitting unit.

[0013] Optionally, the light-emitting layer further includes a P-type barrier layer; the light-emitting layer is grown on the N-type conductive layer, comprising: Layer unit structures and P-type barrier layers are alternately grown on the N-type conductive layer; the layer unit structures are arranged adjacent to the N-type conductive layer.

[0014] Optionally, after growing a P-type conductive layer on the light-emitting layer, the method further includes: A tunnel junction insertion layer is grown on the side of the P-type conductive layer away from the substrate.

[0015] The technical solution of this invention, by setting a first AlGaN layer and a second AlGaN layer on two sides of the quantum well layer, allows the second AlGaN layer to block the influence of subsequent high-temperature process conditions on the quantum well layer, reducing the probability of In component desorption during the high-temperature barrier layer growth process. This effectively reduces the accumulation of compressive stress in the quantum well, suppresses the migration and segregation of In atoms at high temperatures, and improves the uniformity of In component in the quantum well layer. Simultaneously, the first AlGaN layer cuts off the direct diffusion channel between the quantum well layer and the N-type conductive layer, and together with the second AlGaN layer, forms a "sandwiching" effect on the quantum well layer. This improves the heat resistance of the light-emitting layer, reduces the influence of the subsequent growth process on the initially grown light-emitting units, and improves the quality of the epitaxial structure. When forming a full-color Micro-LED chip, the manufacturing process can be simplified while ensuring the quality of the full-color Micro-LED chip, thus reducing the manufacturing cost. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an epitaxial structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a light-emitting layer provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of another epitaxial structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of another light-emitting layer structure provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of another epitaxial structure provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of a tunneling junction insertion layer provided in an embodiment of the present invention; Figure 7 A photoluminescence test image of an epitaxial structure provided in an embodiment of the present invention; Figure 8 This is a flowchart illustrating a method for fabricating an epitaxial structure according to an embodiment of the present invention. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0018] In current technology, LED structures remain limited to monochromatic epitaxial structures. This is primarily because the inconsistent growth conditions of the various epitaxial layers in a full-color LED system can lead to mutual interference. In particular, the growth of the upper layer can affect the stability of the lower epitaxial structure. For example, the high-temperature growth of the upper N-GaN layer can affect the stability of the quantum well in the lower epitaxial layer, causing In deposition, etc. When using a vertically stacked pixel scheme to stack multiple monochromatic epitaxial structures to form a full-color Micro-LED chip, it relies on equipment precision and process yield, and the process is complex, increasing the manufacturing cost of the full-color Micro-LED chip.

[0019] To address the aforementioned technical problems, embodiments of the present invention provide an epitaxial structure. Figure 1 This is a schematic diagram of an epitaxial structure provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of a light-emitting layer provided in an embodiment of the present invention. Figure 1 and Figure 2 As shown, the epitaxial structure includes at least two stacked light-emitting units 10; each light-emitting unit 10 includes a stacked N-type conductive layer 11, a light-emitting layer 12, and a P-type conductive layer 13; the light-emitting layer 12 includes at least one layer unit structure 121; each layer unit structure 121 includes at least two sequentially stacked quantum wells 1211, each quantum well 1211 includes a well layer 12111 and a barrier layer 12112, and a first AlGaN layer 12113 and a second AlGaN layer 12114 disposed on both sides of the well layer 12111, the second AlGaN layer 12114 being disposed between the well layer 12111 and the barrier layer 12112.

[0020] Specifically, Figure 1 The example illustrates an epitaxial structure comprising two stacked light-emitting units 10, namely a first light-emitting unit 101 and a second light-emitting unit 102, wherein the first light-emitting unit 101 is closer to the substrate 103 than the second light-emitting unit 102. The emission color of the first light-emitting unit 101 and the emission color of the second light-emitting unit 102 may be different, in which case the process conditions for forming the first light-emitting unit 101 are different from those for forming the second light-emitting unit 102. Each light-emitting unit 10 includes at least one layer unit structure 121. For example, Figure 2The illustration exemplifies that both the first light-emitting unit 101 and the second light-emitting unit 102 include a stacked layer unit structure 121. Each layer unit structure 121 includes at least two quantum wells 1211 stacked sequentially. Each quantum well 1211 includes a first AlGaN layer 12113, a well layer 12111, a second AlGaN layer 12114, and a barrier layer 12112 stacked sequentially. The well layer 12111 may include an InGaN layer, and the barrier layer 12112 may include a GaN layer. The well layer 12111 is surrounded on both sides by the AlGaN layer, forming a three-dimensional diffusion barrier. The barrier height of the AlGaN layer is greater than that of the GaN layer, and it exhibits higher temperature stability. After the AlGaN layer encapsulates the well layer 12111, during the formation of the next light-emitting unit 10, the second AlGaN layer 12114 can block the influence of subsequent high-temperature processing conditions on the well layer 12111, reducing the probability of In component in the well layer 12111 desorbing during the high-temperature growth of the barrier layer 12112. This effectively reduces the accumulation of compressive stress in the quantum well 1211, suppresses the migration and segregation of In atoms at high temperatures, and improves the uniformity of In component in the well layer 12111. Simultaneously, the first AlGaN layer 12113 cuts off the direct diffusion channel between the well layer 12111 and the N-type conductive layer 11, and together with the second AlGaN layer 12114, forms a "clamping" effect on the well layer 12111. This improves the heat resistance of the light-emitting layer 12. When the epitaxial structure includes at least two stacked light-emitting units 10, the influence of the subsequent growth process of the light-emitting unit 10 on the initially grown light-emitting unit 10 can be reduced, improving the quality of the epitaxial structure. When forming full-color Micro-LED chips, the manufacturing process can be simplified while ensuring the quality of the full-color Micro-LED chips, thereby reducing the manufacturing cost of full-color Micro-LED chips.

[0021] For example, Figure 2 The example shown illustrates a layer cell structure 121 comprising two quantum wells 1211. In other embodiments, the layer cell structure 121 may include 2 to 15 quantum wells 1211, without limitation herein. Figure 1 The example illustrates an epitaxial structure comprising two stacked light-emitting units 10. The first light-emitting unit 10 is grown preferentially before the second light-emitting unit 10. By wrapping both sides of the well layer 12111 with an AlGaN layer, the impact of the process for growing the second light-emitting unit 102 on the first light-emitting unit 101 can be reduced. In other embodiments, the epitaxial structure may further comprise three stacked light-emitting units 10. Figure 3 This is a schematic diagram of another epitaxial structure provided in an embodiment of the present invention. For example... Figure 3As shown, the epitaxial structure includes a first light-emitting unit 101, a second light-emitting unit 102, and a third light-emitting unit 104 sequentially stacked on a substrate 103. During the growth of the epitaxial structure, the first light-emitting unit 101, the second light-emitting unit 102, and the third light-emitting unit 104 can be grown sequentially on the substrate 103. By wrapping both sides of the well layer 12111 with an AlGaN layer, the impact of the process for growing the second light-emitting unit 102 on the first light-emitting unit 101 can be reduced, and the impact of the process for growing the third light-emitting unit 104 on both the second light-emitting unit 102 and the first light-emitting unit 101 can also be reduced.

[0022] The technical solution of this embodiment, by setting a first AlGaN layer and a second AlGaN layer on the two layers of the quantum well layer, allows the second AlGaN layer to block the influence of subsequent high-temperature process conditions on the well layer, reducing the probability of In component desorption during the high-temperature barrier layer growth process in the well layer. This effectively reduces the accumulation of compressive stress in the quantum well, suppresses the migration and segregation of In atoms at high temperatures, and improves the uniformity of In component in the well layer. Simultaneously, the first AlGaN layer cuts off the direct diffusion channel between the well layer and the N-type conductive layer, and together with the second AlGaN layer, forms a "sandwiching" effect on the well layer. This improves the heat resistance of the light-emitting layer, reduces the influence of the subsequent growth process on the initially grown light-emitting units, and improves the quality of the epitaxial structure. When forming a full-color Micro-LED chip, the fabrication process can be simplified while ensuring the quality of the full-color Micro-LED chip, thus reducing the manufacturing cost.

[0023] Continue to refer to Figure 1 The epitaxial structure also includes a substrate 103. Along the direction X from the substrate 103 toward the light-emitting unit 10, the Al composition in the AlGaN layer of the light-emitting unit 10 closer to the substrate 103 is less than the Al composition in the AlGaN layer of the light-emitting unit 10 farther from the substrate 103.

[0024] Specifically, along the direction X from the substrate 103 to the light-emitting unit 10, the emission wavelength of the light-emitting unit 10 closer to the substrate 103 is shorter than that of the light-emitting unit 10 farther from the substrate 103. A higher Al content in the AlGaN layer results in better temperature stability. By setting the Al content in the AlGaN layer of the light-emitting unit 10 closer to the substrate 103 to be less than that of the light-emitting unit 10 farther from the substrate 103, the heat resistance of the quantum well 121 in the light-emitting unit 10 can be improved even as the emission wavelength of the light-emitting unit 10 increases, thus improving the quality of the epitaxial structure. When forming a full-color Micro-LED chip, the manufacturing process can be simplified while maintaining the quality of the full-color Micro-LED chip, reducing the manufacturing cost. For example... Figure 1As shown, the first light-emitting unit 101 is a light-emitting unit 10 close to the substrate 103, and the second light-emitting unit 102 is a light-emitting unit 10 away from the substrate 103. The emission wavelength of the first light-emitting unit 101 is smaller than the emission wavelength of the second light-emitting unit 102. In this case, the Al composition of the AlGaN layer in the first light-emitting unit 101 can be set to be smaller than the Al composition of the AlGaN layer in the second light-emitting unit 102, which can improve the heat resistance of the quantum well 1211 in the second light-emitting unit 102 and improve the quality of the epitaxial structure. The AlGaN layer in the light-emitting unit 10 may include at least one of a first AlGaN layer 12113 and a second AlGaN layer 12114.

[0025] It should be noted that in some embodiments, such as Figure 3 As shown, when the epitaxial structure includes three sequentially stacked first light-emitting units 101, second light-emitting units 102, and third light-emitting units 104, the emission wavelength of the first light-emitting unit 101 is smaller than that of the second light-emitting unit 102, and the emission wavelength of the second light-emitting unit 102 is smaller than that of the third light-emitting unit 104. For example, the first light-emitting unit 101, the second light-emitting unit 102, and the third light-emitting unit 104 are respectively a blue light-emitting unit, a green light-emitting unit, and a red light-emitting unit. In this case, the Al content of the AlGaN layer in the first light-emitting unit 101 can be set to be smaller than that in the AlGaN layer in the second light-emitting unit 102, and the Al content of the AlGaN layer in the second light-emitting unit 102 can be smaller than that in the AlGaN layer in the third light-emitting unit 104. This can improve the heat resistance of the quantum well 1211 in the light-emitting unit 10 when the emission wavelength of the light-emitting unit 10 increases, thereby improving the quality of the epitaxial structure.

[0026] Figure 4 This is a schematic diagram of another light-emitting layer structure provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the light-emitting layer 12 includes at least two layer unit structures 121, and the light-emitting layer 12 also includes a P-type barrier layer 122; the P-type barrier layer 122 and the layer unit structure 121 are alternately arranged.

[0027] Specifically, the layer unit structure 121 includes at least two closely packed quantum wells 1211, forming a "well group". The wave functions of each quantum well in the "well group" couple, forming a microstrip, enabling specialized bandgap engineering and thus allowing for bandgap and stress modulation. The "well group" is then alternately arranged with a P-type barrier layer 122, achieving multi-quantum well coupling. The P-type barrier layer 122 improves the hole injection efficiency in the "well group", enhancing the internal quantum efficiency (IEQ) of the light-emitting layer 12, thereby improving the performance of the epitaxial structure and facilitating the realization of high-quality full-color Micro-LED chips. For example, the P-type barrier layer 122 includes a p-AlGaN layer or a p-AlGaInN layer. Figure 4 As shown, the light-emitting layer 12 may include two layer unit structures 121 and two P-type barrier layers 122. The two P-type barrier layers 122 are respectively disposed on one side of one layer unit structure 121, realizing the alternating arrangement of the layer unit structure 121 and the P-type barrier layer 122. Each layer unit structure 121 includes two stacked quantum wells 1211. When the light-emitting layer 12 includes a P-type barrier layer 122, each layer unit structure 121 may include 2-4 quantum wells 1211, and the periodic arrangement number of the layer unit structure 121 and the P-type barrier layer 122 can be 2-5.

[0028] It should be noted that, Figure 4 The example shown illustrates that the number of quantum wells 1211 in each layer unit structure 121 is the same, and the number of layer unit structures 121 in the light-emitting layer 12 of each light-emitting unit 10 is the same. In other embodiments, the number of quantum wells 1211 in each layer unit structure 121 may be different, and the number of layer unit structures 121 in the light-emitting layer 12 of each light-emitting unit 10 may be different.

[0029] Figure 5 This is a schematic diagram of another epitaxial structure provided in an embodiment of the present invention. For example... Figure 5 As shown, the epitaxial structure also includes at least one tunneling junction insertion layer 20; the tunneling junction insertion layer 20 and the light-emitting unit 10 are alternately arranged.

[0030] Specifically, the tunneling junction insertion layer 20 is disposed on the side of the light-emitting unit 10 away from the substrate 103, which can increase the tunneling probability of electrons transported by the light-emitting unit 10 to the side away from the substrate 103, realizing the ohmic contact mode of the full tunneling structure of the epitaxial structure and increasing the current density of the light-emitting unit 10. At the same time, it avoids the need for ohmic contact layers between adjacent light-emitting units 10 in the epitaxial structure, reducing the fabrication time and cost of the full-color Micro-LED chip. For example, as... Figure 5As shown, when the epitaxial structure includes a first light-emitting unit 101, a second light-emitting unit 102, and a third light-emitting unit 104 sequentially stacked on the substrate 103, the epitaxial structure includes three tunnel junction insertion layers 20, which are respectively disposed on the side of the first light-emitting unit 101 near the second light-emitting unit 102, the side of the second light-emitting unit 102 near the third light-emitting unit 104, and the side of the third light-emitting unit 104 away from the second light-emitting unit 102.

[0031] Figure 6 This is a schematic diagram of a tunnel junction insertion layer provided in an embodiment of the present invention, as shown below. Figure 6 As shown, the tunneling junction insertion layer 20 includes a first P-type doped layer 21, a second P-type doped layer 22, a first N-type doped layer 23, and a second N-type doped layer 24 stacked sequentially; the band gap of the second P-type doped layer 22 is smaller than the band gap of the first P-type doped layer 21; the band gap of the first N-type doped layer 23 is smaller than the band gap of the second N-type doped layer 24.

[0032] Specifically, the first P-type doped layer 21 can be a heavily P-type doped GaN layer, denoted as P++GaN layer. The second N-type doped layer 24 can be a heavily N-type doped GaN layer, denoted as N++GaN layer. The first P-type doped layer 21 and the second N-type doped layer 24 form a tunneling junction to increase the tunneling probability of electrons transported by the light-emitting unit 10 to the side away from the substrate 103. At the same time, the band gap of the second P-type doped layer 22 is smaller than the band gap of the first P-type doped layer 21; the band gap of the first N-type doped layer 23 is smaller than the band gap of the second N-type doped layer 24, so that the second P-type doped layer 22 and the first N-type doped layer 23 form a semiconductor layer with a relatively small band gap, and are nested between the tunneling junction formed by the first P-type doped layer 21 and the second N-type doped layer 24, forming a PIN-type superlattice tunneling heterojunction. This can significantly reduce the barrier height of the tunnel junction formed by the first P-type doped layer 21 and the second N-type doped layer 24, creating a locally low barrier. This reduces the voltage required for electrons to pass through the tunnel junction insertion layer 20, thereby reducing the power consumption of the epitaxial structure. For example, the voltage required for the tunnel junction insertion layer 20 is approximately 0.1~0.2V.

[0033] In some embodiments, the first P-type doped layer 21 and the second N-type doped layer 24 comprise GaN layers, and the second P-type doped layer 22 and the first N-type doped layer 23 comprise InGaN layers; the In content in the InGaN layer is less than 20%.

[0034] Specifically, the In content of the InGaN layer can reduce the bandgap of the second P-type doped layer 22 and the first N-type doped layer 23. The higher the In content, the smaller the bandgap of the second P-type doped layer 22 and the first N-type doped layer 23. In addition, an In content of less than 20% in the InGaN layer can reduce the probability of high-density defects caused by large lattice mismatch between the second P-type doped layer 22 and the first N-type doped layer 23 and the first P-type doped layer 21 and the second N-type doped layer 24.

[0035] In some embodiments, the thickness of the second P-type doped layer 22 and the first N-type doped layer 23 can be in the range of 5-10 nm, so that the semiconductor layer nested between the tunnel junction formed by the first P-type doped layer 21 and the second N-type doped layer 24 is extremely thin, which can further reduce the tunneling barrier height and further reduce the voltage division of the tunnel junction insertion layer 20.

[0036] Continue to refer to Figure 5 An n-GaN layer is also disposed on the side of the last tunnel junction insertion layer 20 away from the substrate 103, which can improve the lateral current average of the epitaxial structure and further improve the conductivity of the epitaxial structure. For example, when the light-emitting layer 12 of the epitaxial structure includes three stacked light-emitting units 10 and a tunnel junction insertion layer 20, the light-emitting colors of the three light-emitting units 10 are blue, green, and red, respectively. The light-emitting layer 12 in each light-emitting unit 10 includes a layer unit structure 121 and a P-type barrier layer 122. The layer unit structure 121 includes a first AlGaN layer 12113, a well layer 12111, a second AlGaN layer 12114, and a barrier layer 12112. When the tunnel junction insertion layer 20 includes a first P-type doped layer 21, a second P-type doped layer 22, a first N-type doped layer 23, and a second N-type doped layer 24, photoluminescence (PL) testing of the epitaxial structure can be performed. Figure 7 This is a photoluminescence test image of an epitaxial structure provided in an embodiment of the present invention. The horizontal axis represents wavelength, and the vertical axis represents light intensity. Figure 7 As shown, the three light-emitting units 10 of the epitaxial structure emit blue, green and red colors respectively, achieving a full-color effect for the epitaxial structure.

[0037] This invention also provides a method for fabricating an epitaxial structure, used to fabricate the epitaxial structure provided in any embodiment of this invention. Figure 8 This is a schematic flowchart illustrating a method for fabricating an epitaxial structure according to an embodiment of the present invention. Figure 8 As shown, the method for fabricating this epitaxial structure includes: S110, An N-type conductive layer for the first light-emitting unit is grown on the substrate.

[0038] Specifically, before growing the N-type conductive layer 11 of the first light-emitting unit 101 on the substrate 103, the substrate 103 (which can be sapphire, silicon, silicon carbide, or patterned sapphire, etc.) can be cleaned. Then, a buffer layer 105 is deposited on the substrate 103 using metal-organic chemical vapor deposition (MOCVD) to reduce the lattice mismatch between the substrate 103 and the N-type conductive layer 11. The buffer layer 105 can be a multilayer structure composed of an AlN layer, an AlGaN layer, and a u-GaN layer. The thickness of the AlN layer is 10-400 nm, the thickness of the AlGaN layer is 100-500 nm, the thickness of the u-GaN layer is 1-3 μm, and the growth temperature of the u-GaN layer is 1000-1150 °C.

[0039] After growing the buffer layer 105, a silicon-doped n-GaN layer is grown on the buffer layer 105, becoming the N-type conductive layer 11 of the first light-emitting unit 10. The thickness of the n-GaN layer is 2-3.5 μm, and the growth temperature is 1040-1100℃. The silicon doping concentration is 1E18-3E19 / cm³. 2 .

[0040] S120. A light-emitting layer is grown on the N-type conductive layer of the first light-emitting unit; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer.

[0041] Specifically, when the light-emitting layer 12 only includes layer unit structures 121, quantum wells 1211, consisting of a first AlGaN layer 12113, a well layer 12111, a second AlGaN layer 12114, and a barrier layer 12112, can be grown on the N-type semiconductor layer 11. The number of quantum well pairs 1211 is 2-15. The barrier layer 12112 can be a GaN layer with a thickness of 3-10 nm. The well layer 12111 can be an InGaN layer with a thickness of 1-4 nm and a growth temperature of 750-900℃. The In doping ratio is 0.1-0.18. The first AlGaN layer 12113 and the second AlGaN layer 12114 are AlGaN layers. x Ga 1-x The N-layer has a thickness of 0.5~3nm and a growth temperature of 900~1000℃, with 0≤x≤0.2. The first luminescent layer can emit blue light with a dominant wavelength range of 450~470nm.

[0042] S130. A P-type conductive layer is grown on the light-emitting layer of the first light-emitting unit.

[0043] Specifically, before growing the P-type conductive layer 13 on the first light-emitting layer 12, the first electron blocking layer (EBL) can be grown on the first light-emitting layer 12. The electron blocking layer can be a Mg-doped P-type AlGaN layer with a thickness of 30-120 nm and a growth temperature of 900-1030℃.

[0044] Then, a Mg-doped P-GaN layer is grown on the electron blocking layer, becoming the P-type conductive layer 13 of the first light-emitting unit 10. The thickness of the P-GaN layer is 50-200 nm, and the growth temperature is 930-980℃. The Mg doping concentration is 1E19-5E19 / cm³. 2 .

[0045] In some embodiments, the growth temperature of the p-type conductive layer 13 can be kept constant, the Mg doping concentration can be increased, and a p+GaN layer can continue to grow as a capping layer for the first light-emitting unit 10, thereby improving the conductivity of the light-emitting unit 10. The thickness of the capping layer is 10-30 nm, and the Mg doping concentration is 8E19-2E20 / cm². 2 .

[0046] S140. An N-type conductive layer for the next light-emitting unit is grown on the side of the previous light-emitting unit away from the substrate, where the P-type conductive layer is located.

[0047] Specifically, after growing the first light-emitting unit 10, the next light-emitting unit 10 can be grown on the P-type conductive layer of the previous light-emitting unit 10. For example, when the previous light-emitting unit 10 is the first light-emitting unit 10, the next light-emitting unit 10 is the second light-emitting unit 10. When the previous light-emitting unit 10 is the second light-emitting unit 10, the next light-emitting unit 10 is the third light-emitting unit 10. During the growth of the next light-emitting unit 10, a silicon-doped n-GaN layer is first grown on the side of the previous light-emitting unit 10 away from the substrate 103, serving as the N-type conductive layer 11 for the next light-emitting unit 10. The thickness of the n-GaN layer is 100-400 nm, and the growth temperature is 1000-1100 °C. The silicon doping concentration is 1E18-3E19 / cm³. 2 .

[0048] S150. A light-emitting layer is grown on the N-type conductive layer of the next light-emitting unit; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer.

[0049] Specifically, when the light-emitting layer 12 only includes layer unit structures 121, the light-emitting layer 12 of the next light-emitting unit 10 can be grown on the N-type conductive layer 11 of the next light-emitting unit 10, that is, a quantum well 1211 consisting of a first AlGaN layer 12113, a well layer 12111, a second AlGaN layer 12114, and a barrier layer 12112 can be grown, with 2-15 pairs of quantum wells 12111. The barrier layer 12112 can be a GaN layer with a thickness of 3-10 nm. The well layer 12111 can be an InGaN layer with a thickness of 1-4 nm and a growth temperature of 750-900℃. The In doping ratio is 0.12~0.28. The first AlGaN layer 12113 and the second AlGaN layer 12114 are AlGaN layers. y Ga 1- y The N-layer has a thickness of 0.5~3nm, a growth temperature of 900~1000℃, and a 0.2≤y≤0.35. The second luminescent layer can emit green light with a dominant wavelength range of 520~540nm.

[0050] S160. Grow a P-type conductive layer on the light-emitting layer of the next light-emitting unit.

[0051] Specifically, after the light-emitting layer 12 of the next light-emitting unit 10 is formed, an electron blocking layer (EBL) can be grown on the light-emitting layer 12 of the next light-emitting unit 10. The electron blocking layer can be a Mg-doped P-type AlGaN layer with a thickness of 30-120 nm and a growth temperature of 900-1030 °C. Then, a Mg-doped P-GaN layer is grown on the electron blocking layer to become the P-type conductive layer 13 of the next light-emitting unit 10. The thickness of the P-GaN layer is 50-200 nm and the growth temperature is 930-980 °C. The Mg doping concentration is 1E19-5E19 / cm³. 2 Then, while maintaining the growth temperature of the p-type conductive layer 13, the Mg doping concentration was increased to continue growing the p+GaN layer, which serves as the capping layer for the next light-emitting unit 10. The thickness of the capping layer is 10-30 nm, and the Mg doping concentration is 8E19-2E20 / cm². 2 .

[0052] It should be noted that when the epitaxial structure includes three sequentially stacked light-emitting units 10, after the formation of the second light-emitting unit 10, the N-type semiconductor layer 11, the light-emitting layer 12, and the P-type semiconductor layer 13 of the third light-emitting unit 10 can be sequentially grown on the side of the second light-emitting unit 10 away from the substrate 103. When growing the N-type semiconductor layer 11 of the third light-emitting unit 10, the thickness of the n-GaN layer is 100-400 nm, and the growth temperature is 1000-1100 °C. The silicon doping concentration is 1E18-3E19 / cm³. 2When growing the light-emitting layer 12 of the third light-emitting unit 10, and the light-emitting layer 12 only includes the layer unit structure 121, a quantum well 1211 consisting of a first AlGaN layer 12113, a well layer 12111, a second AlGaN layer 12114, and a barrier layer 12112 can be grown on the third N-type semiconductor layer 11. The number of quantum well pairs 1211 is 2-15. The barrier layer 12112 can be a GaN layer with a thickness of 3-10 nm. The well layer 12111 can be an InGaN layer with a thickness of 1-4 nm and a growth temperature of 750-900℃. The In doping ratio is 0.29-0.45. The first AlGaN layer 12113 and the second AlGaN layer 12114 are AlGaN layers. z Ga 1-z The N-layer has a thickness of 0.5–3 nm and a growth temperature of 900–1000 °C, with a z-value of 0.35 ≤ z ≤ 0.6. The third emitting layer emits red light with a dominant wavelength range of 600–640 nm. An electron blocking layer (EBL) is then grown on the third emitting layer 12. This EBL can be a Mg-doped P-type AlGaN layer with a thickness of 30–120 nm and a growth temperature of 900–1030 °C. Next, a Mg-doped P-GaN layer is grown on the third EBL, forming the P-type conductive layer 13 of the next emitting unit 10. The P-GaN layer has a thickness of 50–200 nm and a growth temperature of 930–980 °C. The Mg doping concentration is 1E19–5E19 / cm³. 2 Then, while maintaining the growth temperature of the p-type conductive layer 13, the Mg doping concentration was increased to continue growing the p+GaN layer, which serves as the capping layer for the next light-emitting unit 10. The thickness of the capping layer is 10-30 nm, and the Mg doping concentration is 8E19-2E20 / cm². 2 .

[0053] In some embodiments, the light-emitting layer 12 further includes a P-type barrier layer 122. Growing the light-emitting layer on the N-type conductive layer includes: Layer unit structures and P-type barrier layers are alternately grown on an N-type conductive layer; the layer unit structures are arranged adjacent to the N-type conductive layer.

[0054] Specifically, when the light-emitting layer 12 includes a P-type barrier layer 122, in step S120, after growing a layer unit structure 121 on the first N-type conductive layer 11, a P-type barrier layer 122 can be grown on the layer unit structure 121. The P-type barrier layer 122 can be a p-AlGaN layer or a p-AlGaInN layer. The thickness of the P-type barrier layer 122 can be 2~8nm. After growing the P-type barrier layer 122, a second layer unit structure 121 can be grown, and then the P-type barrier layer 122 can be grown, so that the layer unit structure 121 and the P-type barrier layer 122 are grown alternately. Similarly, in step S150, after growing a layer unit structure 121 on the second N-type conductive layer 11, a P-type barrier layer 122 can be grown on the layer unit structure 121. After growing the P-type barrier layer 122, a second layer unit structure 121 can be grown, and then the P-type barrier layer 122 can be grown, so that the layer unit structure 121 and the P-type barrier layer 122 grow alternately.

[0055] It should be noted that when the epitaxial structure includes a third light-emitting unit 10, and the light-emitting layer 12 of the third light-emitting unit 10 also includes a P-type barrier layer 122, a layer unit structure 121 can be grown on the third N-type conductive layer 11 during the formation of the light-emitting layer 12 of the third light-emitting unit 10, and then a P-type barrier layer 122 can be grown on the layer unit structure 121. After growing the P-type barrier layer 122, a second layer unit structure 121 can be grown, and then the P-type barrier layer 122 can be grown, so that the layer unit structure 121 and the P-type barrier layer 122 are grown alternately. The number of layer unit structures 121 and P-type barrier layers 122 in different light-emitting units 10 can be the same or different, and this is not limited here.

[0056] In some embodiments, the epitaxial structure further includes a tunnel junction insertion layer. After growing a P-type conductive layer on the light-emitting layer, the structure further includes: A tunnel junction insertion layer is grown on the side of the P-type conductive layer away from the substrate.

[0057] Specifically, when the epitaxial structure includes a tunneling junction insertion layer 20, the tunneling junction insertion layer 20 is disposed on the side of the light-emitting unit 10 away from the substrate 103. After step S130, the tunneling junction insertion layer 20 can be grown first on the side of the P-type conductive layer 13 away from the substrate 103, and then the N-type conductive layer 11 of the next light-emitting unit 10 can be grown on the tunneling junction insertion layer 20. When a capping layer is grown on the P-type conductive layer 13, the tunneling junction insertion layer 20 can be grown on the capping layer. When the tunneling junction insertion layer 20 includes a first P-type doped layer 21, a second P-type doped layer 22, a first N-type doped layer 23, and a second N-type doped layer 24 stacked together, they can be P++ GaN layers / p++ In layers, respectively. w Ga 1-w N layers / n++Inw Ga 1-w N layers / n++GaN layers. Where In w Ga 1-w The In content (w) in the N-layer is in the range of 0 ≤ w ≤ 0.2. The P++ GaN layer is grown at a temperature of 930-980℃ and uses delta doping to increase the Mg doping concentration. The thickness is 10-20 nm, and the Mg concentration is 1E20-5E20 / cm³. 2 After the P++ GaN layer growth is complete, an optimized growth interruption and interface cleaning step is performed (e.g., in an H2 atmosphere, at 920°C, for 10–30 seconds) to remove surface Mg; p++In w Ga 1-w N layers / n++In w Ga 1-w The N-layer growth temperature is 820-930℃, and doping is performed using Mg and Si, respectively, with p++In. w Ga 1-w The thickness of the N layer is 1-6 nm, and the Mg concentration is 6E19-1E20 / cm³. 2 Similarly, after the P++InGaN layer growth is complete, an optimized growth interruption and interface cleaning step is performed (e.g., in an H2 atmosphere, at 920°C, for 10–30 seconds) to remove surface Mg and n++In. w Ga 1-w The N-layer has a thickness of 1-6 nm and is doped with Si at a concentration of 5E19-1E20 / cm². 2 Then, the temperature was raised to 1000℃-1060℃, and a delta growth mode was used to grow a highly silicon-doped n++ GaN layer. The thickness of the n++ GaN layer was 10-25 nm, and the silicon doping concentration was 1E20-5E20 / cm². 2 .

[0058] It should be noted that when the epitaxial structure includes at least two light-emitting units 10, after each light-emitting unit 10 is grown, a tunneling junction insertion layer 20 can be grown on the light-emitting unit 10. Then, the next light-emitting unit 10 can be grown on the tunneling junction insertion layer 20, and finally, a tunneling junction insertion layer 20 can be grown on the next light-emitting unit 10, achieving alternating growth of the light-emitting units 10 and the tunneling junction insertion layer 20. After growing the last tunneling junction insertion layer 20, a silicon-doped n-GaN layer can be grown on the last tunneling junction insertion layer 20. The thickness of the n-GaN layer is 100-400 nm, and the growth temperature is 1000-1100℃. The silicon doping concentration is 1E18-6E19 / cm². 2 .

[0059] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. An epitaxial structure, characterized in that, It includes at least two stacked light-emitting units; each light-emitting unit includes an N-type conductive layer, a light-emitting layer and a P-type conductive layer stacked together; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer.

2. The epitaxial structure according to claim 1, characterized in that, It also includes a substrate; along the direction from the substrate to the light-emitting unit, the Al composition in the AlGaN layer of the light-emitting unit closer to the substrate is less than the Al composition in the AlGaN layer of the light-emitting unit farther from the substrate.

3. The epitaxial structure according to claim 1 or 2, characterized in that, The light-emitting layer includes at least two of the layer unit structures, and the light-emitting layer further includes a P-type barrier layer; the P-type barrier layer and the layer unit structures are alternately arranged.

4. The epitaxial structure according to claim 3, characterized in that, The P-type barrier layer includes a p-AlGaN layer or a p-AlGaInN layer.

5. The epitaxial structure according to claim 1, characterized in that, It also includes at least one tunneling junction insertion layer; the tunneling junction insertion layer and the light-emitting unit are alternately arranged.

6. The epitaxial structure according to claim 5, characterized in that, The tunneling junction insertion layer includes a first P-type doped layer, a second P-type doped layer, a first N-type doped layer, and a second N-type doped layer stacked sequentially; the band gap of the second P-type doped layer is smaller than the band gap of the first P-type doped layer; the band gap of the first N-type doped layer is smaller than the band gap of the second N-type doped layer.

7. The epitaxial structure according to claim 6, characterized in that, The first P-type doped layer and the second N-type doped layer comprise GaN layers, and the second P-type doped layer and the first N-type doped layer comprise InGaN layers; the In content in the InGaN layer is less than 20%.

8. A method for fabricating an epitaxial structure, used to fabricate the epitaxial structure according to any one of claims 1-7; characterized in that, include: An N-type conductive layer of the first light-emitting unit is grown on the substrate; A light-emitting layer is grown on the N-type conductive layer of the first light-emitting unit; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer; A P-type conductive layer is grown on the light-emitting layer of the first light-emitting unit; An N-type conductive layer for the next light-emitting unit is grown on the side of the P-type conductive layer of the previous light-emitting unit that is away from the substrate. A light-emitting layer is grown on the N-type conductive layer of the next light-emitting unit; the light-emitting layer includes at least one layer unit structure; each layer unit structure includes at least two quantum wells stacked sequentially, each quantum well includes a well layer and a barrier layer, and a first AlGaN layer and a second AlGaN layer disposed on both sides of the well layer, the second AlGaN layer being disposed between the well layer and the barrier layer; A P-type conductive layer is grown on the light-emitting layer of the next light-emitting unit.

9. The method for fabricating an epitaxial structure according to claim 8, characterized in that, The light-emitting layer further includes a P-type barrier layer; the light-emitting layer is grown on the N-type conductive layer, including: Layer unit structures and P-type barrier layers are alternately grown on the N-type conductive layer; the layer unit structures are arranged adjacent to the N-type conductive layer.

10. The method for fabricating an epitaxial structure according to claim 8, characterized in that, After growing a P-type conductive layer on the light-emitting layer, the method further includes: A tunnel junction insertion layer is grown on the side of the P-type conductive layer away from the substrate.

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