LED epitaxial structure and preparation method thereof

Abstract

The invention provides an LED epitaxial structure and a preparation method thereof, and the LED epitaxial structure sequentially comprises a buffer layer, a cut-off layer, a first-type semiconductor layer, an active layer and a second-type semiconductor layer which are located on a substrate from bottom to top. Wherein the second type semiconductor layer sequentially comprises a second type limiting layer, a second type transition layer, a second type current expansion layer and a second type ohmic contact layer from bottom to top. Through the arrangement of the second type transition layer, the problem of material mismatch of the LED can be solved, and the performance of the LED is improved.

Description

Technical Field

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

[0002] LED (Light Emitting Diode) was first commercialized in the 1960s, mainly including red and infrared wavelength LEDs. With the advancement of material technology, the brightness and efficiency of LEDs have continued to improve, allowing LEDs to gradually replace traditional light sources in the fields of lighting, display, and communication. As an efficient and environmentally friendly light source, LED technology has made significant progress in semiconductor materials, device structure, and manufacturing processes, promoting the rapid development of modern lighting and display technologies.

[0003] Material mismatch has a significant impact on LED performance. There may be lattice constant mismatch or thermal expansion coefficient mismatch between different materials used in LEDs. This mismatch will cause stress at the material interface and during the growth process. These stresses may cause lattice defects, affect carrier migration and recombination, and thus affect the efficiency and stability of the LED. Moreover, during the growth process of LEDs, material mismatch makes it more difficult to control the quality and uniformity of the materials, which may result in poor quality of the grown crystals or the formation of areas with many defects, thus affecting the performance of the LED device.

[0004] Therefore, it is necessary to provide an LED epitaxial structure and a preparation method thereof to solve the material mismatch problem of LEDs and improve the performance of LEDs. Summary of the invention

[0005] The object of the present invention is to provide an LED epitaxial structure and a preparation method thereof, so as to solve the material mismatch problem of LED and improve the performance of LED.

[0006] In order to achieve the above-mentioned purpose and other related purposes, the present invention provides an LED epitaxial structure, which includes, from bottom to top: a buffer layer, a cutoff layer, a first-type semiconductor layer, an active layer and a second-type semiconductor layer located on a substrate, wherein the second-type semiconductor layer includes, from bottom to top, a second-type confinement layer, a second-type transition layer, a second-type current spreading layer and a second-type ohmic contact layer.

[0007] Optionally, in the LED epitaxial structure, the material of the second type transition layer includes Ga j Sb t , j+t=1.

[0008] Optionally, in the LED epitaxial structure, the material of the second type transition layer includes Ga 0.5 Sb0.5 .

[0009] Optionally, in the LED epitaxial structure, the second-type transition layer is flattened and independent quantum dots.

[0010] Optionally, in the LED epitaxial structure, the second-type transition layer is a wetting layer.

[0011] Optionally, in the LED epitaxial structure, the thickness of the second-type transition layer is 1 nm to 10 nm.

[0012] Optionally, in the LED epitaxial structure, the doping source of the second type transition layer includes Mg, and its doping concentration is 1E18cm -3 ~5E18cm -3 .

[0013] Optionally, in the LED epitaxial structure, the density of quantum dots in the second transition layer is greater than 1×10 10 cm -2 .

[0014] Optionally, in the LED epitaxial structure, the active layer includes, from bottom to top, a first barrier layer, a multi-quantum well layer and a second barrier layer, and the first barrier layer, the multi-quantum well layer and the second barrier layer are all unintentionally doped layers.

[0015] Optionally, in the LED epitaxial structure, the multi-quantum well layer comprises alternating potential well layers and potential barrier layers, wherein the material of the potential well layer comprises (Al y Ga 1-y ) 0.25 In 0.25 P 0.5 , and 0.1≤y≤0.5; the material of the barrier layer includes (Al q Ga 1-q ) 0.25 In 0.25 P 0.5 , and 0.5≤q≤0.9.

[0016] Optionally, in the LED epitaxial structure, the material of the first barrier layer includes (Al x Ga 1-x ) 0.25 In 0.25 P 0.5 , wherein x is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the first barrier layer is 50nm to 400nm.

[0017] Optionally, in the LED epitaxial structure, the material of the second barrier layer includes (Alw Ga 1-w ) 0.25 In 0.25 P 0.5 , wherein w is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the second barrier layer is 50nm to 400nm.

[0018] Optionally, in the LED epitaxial structure, the material of the second-type confinement layer includes AlInP, and the thickness of the second-type confinement layer is 200 nm to 600 nm.

[0019] Optionally, in the LED epitaxial structure, the material of the second-type current spreading layer includes GaP, the second-type current spreading layer is doped with Mg, and the thickness of the second-type current spreading layer is 500nm to 3000nm.

[0020] Optionally, in the LED epitaxial structure, the second-type ohmic contact layer is doped with carbon, and the thickness of the second-type ohmic contact layer is 50 nm to 200 nm.

[0021] Optionally, in the LED epitaxial structure, the LED epitaxial structure is a red light LED epitaxial structure.

[0022] In order to achieve the above-mentioned object and other related objects, the present invention also provides a method for preparing an LED epitaxial structure, comprising the following steps:

[0023] providing a substrate;

[0024] A buffer layer, a cutoff layer, a first-type semiconductor layer, an active layer and a second-type semiconductor layer are sequentially grown on the substrate, wherein the second-type semiconductor layer includes, from bottom to top, a second-type confinement layer, a second-type transition layer, a second-type current spreading layer and a second-type ohmic contact layer.

[0025] Optionally, in the method for preparing the LED epitaxial structure, the material of the second type transition layer includes Ga j Sb t , j+t=1.

[0026] Optionally, in the method for preparing the LED epitaxial structure, the material of the second type transition layer includes Ga 0.5 Sb 0.5 .

[0027] Optionally, in the method for preparing the LED epitaxial structure, the second-type transition layer is a wetting layer.

[0028] Optionally, in the method for preparing the LED epitaxial structure, the second-type transition layer is flattened and independent quantum dots.

[0029] Optionally, in the method for preparing the LED epitaxial structure, the method for forming the second-type transition layer includes:

[0030] After the step of growing the second type confinement layer, interrupting the group III source and the group V source, and turning on the Ga and Sb sources to grow quantum dots;

[0031] interrupting Ga, Sb sources and doping sources, and performing a thermal cycle annealing process;

[0032] The group III source and the group V source are turned on to grow the second-type current spreading layer. During the growth of the second-type current spreading layer, the mismatch stress is absorbed by the quantum dots, and the quantum dots are flattened to form the second-type transition layer.

[0033] Optionally, in the method for preparing the LED epitaxial structure, when the material of the second-type confinement layer is AlInP, the interrupted Group III sources are Al source and In source, and the Group V source is P source.

[0034] Optionally, in the method for preparing the LED epitaxial structure, the thickness of the second-type transition layer is 1 nm to 10 nm.

[0035] Optionally, in the method for preparing the LED epitaxial structure, the doping source of the second type transition layer includes Mg, and its doping concentration is 1E18cm -3 ~5E18cm -3 .

[0036] Optionally, in the method for preparing the LED epitaxial structure, the density of quantum dots in the second type transition layer is greater than 1×10 10 cm -2 .

[0037] Optionally, in the method for preparing the LED epitaxial structure, the active layer includes a first barrier layer, a multi-quantum well layer and a second barrier layer grown sequentially from bottom to top, and the first barrier layer, the multi-quantum well layer and the second barrier layer are all unintentionally doped layers.

[0038] Optionally, in the method for preparing the LED epitaxial structure, the multi-quantum well layer is formed by alternating growth of a potential well layer and a potential barrier layer, wherein the material of the potential well layer includes (Al y Ga 1-y ) 0.25 In 0.25 P 0.5 , and 0.1≤y≤0.5; the material of the barrier layer includes (Al q Ga 1-q ) 0.25 In 0.25P 0.5 , and 0.5≤q≤0.9.

[0039] Optionally, in the method for preparing the LED epitaxial structure, the material of the first barrier layer includes (Al x Ga 1-x ) 0.25 In 0.25 P 0.5 , wherein x is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the first barrier layer is 50nm to 400nm.

[0040] Optionally, in the method for preparing the LED epitaxial structure, the material of the second barrier layer includes (Al w Ga 1-w ) 0.25 In 0.25 P 0.5 , wherein w is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the second barrier layer is 50nm to 400nm.

[0041] Optionally, in the method for preparing the LED epitaxial structure, the material of the second-type confinement layer includes AlInP, and the thickness of the second-type confinement layer is 200 nm to 600 nm.

[0042] Optionally, in the method for preparing the LED epitaxial structure, the material of the second-type current spreading layer includes GaP, the second-type current spreading layer is doped with Mg, and the thickness of the second-type current spreading layer is 500nm to 3000nm.

[0043] Optionally, in the method for preparing the LED epitaxial structure, the second-type ohmic contact layer is doped with carbon, and the thickness of the second-type ohmic contact layer is 50 nm to 200 nm.

[0044] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0045] The LED epitaxial structure provided by the present invention adopts a second-type transition layer as a transition layer between a second-type limiting layer and a second-type current spreading layer, which can absorb the mismatch stress generated during the growth process to reduce defects caused by stress and improve lattice matching, thereby solving the material mismatch problem of the LED and improving the performance of the LED.

[0046] Secondly, the second-type transition layer of the present invention is flattened and independent quantum dots, and the quantum dots are preferably GaSb quantum dots, which can absorb the mismatch stress generated during the growth process to reduce defects caused by stress and improve lattice matching; the quantum dots are flattened during the growth process to form a second-type transition layer, which can help reduce the interface state density in the heterostructure, thereby improving the transmission of carriers; and GaSb has a type II band structure, which can provide strong spatial confinement for holes compared to the traditional type I band structure, thereby improving the working efficiency of the LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 is a schematic diagram of an LED epitaxial structure according to an embodiment of the present invention;

[0049] Figure 2 is a flow chart of a method for preparing an LED epitaxial structure according to an embodiment of the present invention;

[0050] Figure 3a and Figure 3b is a schematic diagram of forming a second type transition layer according to an embodiment of the present invention;

[0051] Figures 1 to 3b middle:

[0052] 10-substrate, 20-LED epitaxial structure, 201-buffer layer, 202-cutoff layer, 203-first type ohmic contact layer, 204-first type window layer, 205-first type confinement layer, 206-first barrier layer, 207-active layer, 208-second barrier layer, 209-second type confinement layer, 210-second type transition layer, 2101-quantum dot, 211-second type current spreading layer, 212-second type ohmic contact layer. DETAILED DESCRIPTION

[0053] The LED epitaxial structure and the preparation method thereof proposed by the present invention are further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0054] Before describing the embodiments of the present invention, the following contents are described in advance. First, in this specification, a binary material is assumed to be a compound with a fixed chemical composition ratio of 1:1. When it is simply marked as "AlInP", it means that the chemical composition ratio of the sum of Al and In to P is 1:1, and the ratio of Al to In is not fixed. When it is simply marked as "GaInP", it means that the chemical composition ratio of the sum of Ga and In to P is 1:1, and the ratio of Ga to In is not fixed.

[0055] See also Figure 1 The present invention provides an LED epitaxial structure 20, which may include, from bottom to top, a buffer layer 201 located on a substrate 10, a cutoff layer 202, a first-type semiconductor layer, an active layer, and a second-type semiconductor layer.

[0056] In this embodiment, the first-type semiconductor layer may include, from bottom to top, a first-type ohmic contact layer 203 , a first-type window layer 204 , and a first-type confinement layer 205 .

[0057] The active layer may include, from bottom to top, a first barrier layer 206 , a multi-quantum well layer 207 , and a second barrier layer 208 , and the first barrier layer 206 , the multi-quantum well layer 207 , and the second barrier layer 208 are all unintentionally doped layers.

[0058] The second-type semiconductor layer may include, from bottom to top, a second-type confinement layer 209, a second-type transition layer 210, a second-type current spreading layer 211, and a second-type ohmic contact layer 212. In this embodiment, the second-type transition layer is used as a transition layer between the second-type confinement layer and the second-type current spreading layer, which can absorb the mismatch stress generated during the growth process to reduce defects caused by stress and improve lattice matching, thereby solving the material mismatch problem of the LED and improving the performance of the LED.

[0059] In this embodiment, the second-type transition layer 210 is a wetting layer. Further, the second-type transition layer 210 is flattened and mutually independent quantum dots. The quantum dots are preferably GaSb quantum dots, but not limited thereto. The quantum dots can absorb the mismatch stress generated during the growth process to reduce the defects caused by the stress and improve the lattice matching. The second-type transition layer is formed by the flattening of the quantum dots during the growth process, which can help reduce the interface state density in the heterostructure, thereby improving the transmission of carriers. Moreover, GaSb has a type II band structure, which can provide strong spatial confinement for holes compared to the type I band structure of GaP, thereby improving the working efficiency of the LED.

[0060] The LED epitaxial structure 20 of this embodiment is preferably a red LED epitaxial structure. Figure 2The method for preparing the LED epitaxial structure 20 may include the following steps:

[0061] Step S1: providing a substrate 10;

[0062] Step S2: growing a buffer layer 201, a cutoff layer 202, a first-type semiconductor layer, an active layer and a second-type semiconductor layer on the substrate 10 in sequence, wherein the second-type semiconductor layer includes, from bottom to top, a second-type confinement layer 209, a second-type transition layer 210, a second-type current spreading layer 211 and a second-type ohmic contact layer 212.

[0063] In this embodiment, the preparation process of the LED epitaxial structure can be any one of a metal organic chemical vapor deposition (MOCVD) process, a molecular beam epitaxy (MBE) process or an ultra-high vacuum chemical vapor deposition (UHVCVD) process, but is not limited thereto. Further, the preparation process of the LED epitaxial structure is preferably a MOCVD process. The following specific embodiments are described by taking the MOCVD process as an example.

[0064] Step S1 is performed to provide a substrate 10. The substrate 10 is preferably a GaAs (gallium arsenide) substrate, but is not limited thereto.

[0065] Step S2 is performed to sequentially grow a buffer layer 201 , a cutoff layer 202 , and a first-type semiconductor layer on the substrate 10 . The first-type semiconductor layer may sequentially include a first-type ohmic contact layer 203 , a first-type window layer 204 , and a first-type confinement layer 205 from bottom to top.

[0066] After the step of growing the first-type semiconductor layer, an active layer is grown on the first-type semiconductor layer. In this embodiment, the active layer may include a first barrier layer 206, a multi-quantum well layer 207, and a second barrier layer 208 grown in sequence. Therefore, after the step of growing the first-type confinement layer 205, the first barrier layer 206 is grown on the first-type confinement layer 205.

[0067] The material of the first barrier layer 206 is preferably (Al x Ga 1-x ) 0.25 In 0.25 P 0.5 , wherein x is the same as the Al component q in the barrier layer of the multi-quantum well layer 207, that is, the Al component in the first barrier layer 206 is the same as the Al component in the barrier layer of the multi-quantum well layer 207. In this embodiment, a first barrier layer 206 with a thickness of 50nm to 400nm can be grown in the reaction chamber of an MOCVD growth furnace. Preferably, a first barrier layer 206 with a thickness of 100nm is grown. In this embodiment, the first barrier layer 206 is preferably an unintentionally doped layer.

[0068] After the step of growing the first barrier layer 206, the multi-quantum well layer 207 is grown on the first barrier layer 206. In this embodiment, the multi-quantum well layer 207 may include alternating potential well layers and potential barrier layers, and the material of the multi-quantum well layer 207 may be AlGaInP, wherein the material of the potential well layer is preferably (Al y Ga 1-y ) 0.25 In 0.25 P 0.5 , wherein 0.1≤y≤0.5, further, y is preferably 0.2; the material of the barrier layer is preferably (Al q Ga 1-q ) 0.25 In 0.25 P 0.5 , wherein 0.5≤q≤0.9, and further, q is preferably 0.8. In this embodiment, a multi-quantum well layer 207 of 10 to 40 periods can be grown in the reaction chamber of the MOCVD growth furnace, and preferably, a multi-quantum well layer 207 of 20 periods is grown. The growth method of the multi-quantum well layer 207 is to alternately grow a potential well layer and a potential barrier layer. Further, the multi-quantum well layer 207 is an unintentionally doped layer.

[0069] After the step of growing the multi-quantum well layer 207, the second barrier layer 208 is grown on the multi-quantum well layer 207. The material of the second barrier layer 208 is preferably (Al w Ga 1-w ) 0.25 In 0.25 P 0.5 , wherein w is preferably the same as the Al component q in the barrier layer of the multi-quantum well layer 207. In this embodiment, a second barrier layer 208 with a thickness of 50nm to 400nm can be grown in the reaction chamber of the MOCVD growth furnace. Preferably, a second barrier layer 208 with a thickness of 250nm is grown. The second barrier layer 208 in this embodiment is preferably an unintentionally doped layer.

[0070] After the step of growing the active layer, a second-type semiconductor layer is grown on the active layer. In this embodiment, the second-type semiconductor layer may include, from bottom to top, a second-type confinement layer 209, a second-type transition layer 210, a second-type current spreading layer 211, and a second-type ohmic contact layer 212. Therefore, after the step of growing the active layer, a second-type confinement layer 209 is grown on the active layer.

[0071] The material of the second type confinement layer 209 is preferably AlInP, but not limited thereto. The second type confinement layer 209 is doped with a second type dopant, and the second type dopant is preferably Mg, but not limited thereto. In this embodiment, a second type confinement layer 209 with a thickness of 200nm to 600nm can be grown in the reaction chamber of an MOCVD growth furnace. Preferably, a second type confinement layer 209 with a thickness of 300nm is grown.

[0072] After the step of growing the second-type confinement layer 209, a second-type transition layer 210 and a second-type current spreading layer 211 are grown on the second-type confinement layer 209. In this embodiment, the second-type transition layer 210 is disposed between the second-type confinement layer 209 and the second-type current spreading layer 211 to reduce defects caused by stress to improve lattice matching and provide strong spatial confinement for holes.

[0073] In this embodiment, the material of the second type transition layer 210 can be Ga j Sb t , where j+t=1, preferably Ga 0.5 Sb 0.5 . The second-type transition layer 210 is a wetting layer. Further, the second-type transition layer 210 is a flattened and mutually independent quantum dot 2101. The quantum dot 2101 is preferably a GaSb quantum dot, but is not limited thereto. When the quantum dot 2101 is a GaSb quantum dot, the GaSb quantum dot acts as a transition layer between AlInP and GaP materials (or between AlGaInP and GaP materials or between AlGaInP and GaAs materials, etc.), which can absorb the mismatch stress generated during the growth process to reduce defects caused by stress and improve lattice matching; during the growth process, the GaSb quantum dots are flattened to form a second-type transition layer, which can help reduce the interface state density in the heterostructure, thereby improving the transport of carriers; and GaSb is a type II band structure, which can provide strong spatial confinement for holes compared to the type I band structure of GaP, thereby improving the working efficiency of the LED. The following content is explained with the quantum dot 2101 being a GaSb quantum dot.

[0074] See also Figures 3a to 3b , the method for forming the second-type transition layer 210 may include:

[0075] Step S21: after the step of growing the second type confinement layer 209, interrupting the group III source and the group V source, and turning on the Ga and Sb sources to grow the quantum dots 2101;

[0076] Step S22: interrupting Ga, Sb sources and doping sources, and performing a thermal cycle annealing process;

[0077] Step S23: turning on the group III source and the group V source to grow the second-type current spreading layer 211 . During the growth of the second-type current spreading layer 211 , the mismatch stress is absorbed by the quantum dots 2101 , and the quantum dots 2101 are flattened to form the second-type transition layer 210 .

[0078] See also Figure 3a , execute step S21 to grow quantum dots 2101. In this embodiment, the interrupted group III source and group V source are selected specifically according to the material of the second type confinement layer 209. For example, when the material of the second type confinement layer 209 is AlInP, the interrupted group III source is an Al (aluminum) source and an In (indium) source, and the group V source is a P (phosphorus) source. Since the doping source is turned on when the second type confinement layer 209 is grown, the doping source of this step remains turned on. Therefore, the second type transition layer 210 is doped with a second type dopant (doping source), and the second type dopant is preferably Mg, but not limited thereto. Furthermore, the doping concentration of the second type transition layer 210 is preferably 1E18cm -3 ~5E18cm -3 , for example 2E18cm -3 .

[0079] Step S22 is performed to interrupt the Ga, Sb and doping sources after the step of growing the quantum dots 2101, and perform thermal cycle annealing. The density of the quantum dots in the second-type transition layer 210 is greater than 1×10 10 cm -2 Furthermore, the density of the quantum dots is preferably 5×10 10 cm -2 .

[0080] See also Figure 3b , perform step S23, after the step of thermal cycle annealing, grow a second type current spreading layer 211 on the quantum dot 2101. The group III source and the group V source of this step can be selected according to the material of the second type current spreading layer 211. In the process of growing the second type current spreading layer 211, the quantum dot 2101 absorbs the growth stress and flattens to form a second type transition layer 210. Further, the thickness of the second type transition layer 210 is preferably 1nm to 10nm. Due to the influence of the uncontrollable stress direction, the thickness of the second type transition layer 210 is not uniform.

[0081] In this embodiment, the material of the second-type current spreading layer 211 is preferably GaP, but not limited thereto. For example, the material of the second-type current spreading layer 211 can also be AlGaInP, AlInP and AlGaAs, which have smaller mismatch stress than GaP but poor light transmittance. The second current spreading layer 211 is doped with a second-type dopant, and the second-type dopant is preferably Mg, but not limited thereto. In this embodiment, a second current spreading layer 211 with a thickness of 500nm to 3000nm can be grown in the reaction chamber of an MOCVD growth furnace. Preferably, a second-type current spreading layer 211 with a thickness of 2000nm is grown.

[0082] After the step of growing the second-type current spreading layer 211, the second-type ohmic contact layer 212 is grown on the second-type current spreading layer 211. The material of the second-type ohmic contact layer 212 is preferably GaP, but not limited thereto. The second-type ohmic contact layer 212 may be doped with carbon (C). In this embodiment, the second-type ohmic contact layer 212 with a thickness of 50nm to 200nm can be grown in the reaction chamber of the MOCVD growth furnace. Preferably, the second-type ohmic contact layer 212 with a thickness of 100nm is grown.

[0083] In summary, the LED epitaxial structure provided by the present invention adopts a second-type transition layer as a transition layer between the second-type confinement layer and the second-type current spreading layer, and the quantum dots are preferably GaSb quantum dots, which can absorb the mismatch stress generated during the growth process to reduce defects caused by stress and improve lattice matching; the quantum dots are flattened during the growth process to form a second-type transition layer, which can help reduce the interface state density in the heterostructure, thereby improving the transport of carriers; and GaSb has a type II band structure, which can provide strong spatial confinement for holes compared to the type I band structure of GaP, thereby improving the working efficiency of the LED.

[0084] In addition, it is understood that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

[0085] It should also be understood that the present invention is not limited to the specific methods, compounds, materials, manufacturing techniques, usages and applications described herein, which may vary. It should also be understood that the terms described herein are only used to describe specific embodiments, rather than to limit the scope of the present invention. It must be noted that the singular forms "one", "a kind" and "the" used herein and in the appended claims include plural references unless the context clearly indicates the opposite meaning. Thus, for example, a reference to "a step" means a reference to one or more steps, and may include secondary steps. All conjunctions used should be understood in the broadest sense. Therefore, the word "or" should be understood to have the definition of a logical "or", rather than a logical "exclusive or", unless the context clearly indicates the opposite meaning. The structure described herein will be understood to also quote the functional equivalent of the structure. Language that can be interpreted as approximate should be understood as such, unless the context clearly indicates the opposite meaning.

Claims

1. An LED epitaxial structure, characterized in that: The invention comprises, from bottom to top, a buffer layer, a cutoff layer, a first-type semiconductor layer, an active layer and a second-type semiconductor layer on a substrate, wherein the second-type semiconductor layer comprises, from bottom to top, a second-type confinement layer, a second-type transition layer, a second-type current spreading layer and a second-type ohmic contact layer.

2. The LED epitaxial structure according to claim 1, characterized in that: The material of the second type transition layer includes Ga j Sb t , j+t=1.

3. The LED epitaxial structure according to claim 1, characterized in that: The material of the second type transition layer includes Ga 0.5 Sb 0.5 .

4. The LED epitaxial structure according to claim 1, characterized in that: The second-type transition layer is flattened and independent quantum dots.

5. The LED epitaxial structure according to claim 1, characterized in that: The second type transition layer is a wetting layer.

6. The LED epitaxial structure according to claim 1, characterized in that: The thickness of the second-type transition layer is 1 nm to 10 nm.

7. The LED epitaxial structure according to claim 1, characterized in that: The doping source of the second type transition layer includes Mg, and its doping concentration is 1E18cm -3 ~5E18cm -3 .

8. The LED epitaxial structure according to claim 1, characterized in that: The density of quantum dots in the second type transition layer is greater than 1×10 10 cm -2 .

9. The LED epitaxial structure according to claim 1, characterized in that: The active layer includes a first barrier layer, a multi-quantum well layer and a second barrier layer in order from bottom to top, and the first barrier layer, the multi-quantum well layer and the second barrier layer are all unintentionally doped layers.

10. The LED epitaxial structure according to claim 9, characterized in that: The multi-quantum well layer comprises alternating potential well layers and potential barrier layers, wherein the material of the potential well layer comprises (Al y Ga 1-y ) 0.25 In 0.25 P 0.5 , and 0.1≤y≤0.5; the material of the barrier layer includes (Al q Ga 1-q ) 0.25 In 0.25 P 0.5 , and 0.5≤q≤0.

9.

11. The LED epitaxial structure according to claim 10, characterized in that: The material of the first barrier layer includes (Al x Ga 1-x ) 0.25 In 0.25 P 0.5 , wherein x is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the first barrier layer is 50nm to 400nm.

12. The LED epitaxial structure according to claim 10, characterized in that: The material of the second barrier layer includes (Al w Ga 1-w ) 0.25 In 0.25 P 0.5 , wherein w is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the second barrier layer is 50nm to 400nm.

13. The LED epitaxial structure according to claim 1, characterized in that: The material of the second-type confinement layer includes AlInP, and the thickness of the second-type confinement layer is 200 nm to 600 nm.

14. The LED epitaxial structure according to claim 1, characterized in that: The material of the second-type current spreading layer includes GaP, the second-type current spreading layer is doped with Mg, and the thickness of the second-type current spreading layer is 500nm-3000nm.

15. The LED epitaxial structure according to claim 1, characterized in that: The second-type ohmic contact layer is doped with carbon, and the thickness of the second-type ohmic contact layer is 50 nm to 200 nm.

16. The LED epitaxial structure according to claim 1, characterized in that: The LED epitaxial structure is a red light LED epitaxial structure.

17. A method for preparing an LED epitaxial structure, characterized in that: The following steps are involved: providing a substrate; A buffer layer, a cutoff layer, a first-type semiconductor layer, an active layer and a second-type semiconductor layer are sequentially grown on the substrate, wherein the second-type semiconductor layer includes, from bottom to top, a second-type confinement layer, a second-type transition layer, a second-type current spreading layer and a second-type ohmic contact layer.

18. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The material of the second type transition layer includes Ga j Sb t , j+t=1.

19. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The material of the second type transition layer includes Ga 0.5 Sb 0.5 .

20. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The thickness of the second-type transition layer is 1 nm to 10 nm.

21. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The second type transition layer is a wetting layer.

22. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The second-type transition layer is flattened and independent quantum dots.

23. The method for preparing an LED epitaxial structure according to claim 22, characterized in that: The method for forming the second type transition layer comprises: After the step of growing the second type confinement layer, interrupting the group III source and the group V source, and turning on the Ga and Sb sources to grow quantum dots; interrupting Ga, Sb sources and doping sources, and performing a thermal cycle annealing process; The group III source and the group V source are turned on to grow the second-type current spreading layer. During the growth of the second-type current spreading layer, the mismatch stress is absorbed by the quantum dots, and the quantum dots are flattened to form the second-type transition layer.

24. The method for preparing an LED epitaxial structure according to claim 23, characterized in that: When the material of the second-type confinement layer is AlInP, the interrupted Group III sources are Al source and In source, and the Group V source is P source.

25. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The doping source of the second type transition layer includes Mg, and its doping concentration is 1E18cm -3 ~5E18cm -3 .

26. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The density of quantum dots in the second type transition layer is greater than 1×10 10 cm -2 .

27. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The active layer includes a first barrier layer, a multi-quantum well layer and a second barrier layer grown in sequence from bottom to top, and the first barrier layer, the multi-quantum well layer and the second barrier layer are all unintentionally doped layers.

28. The method for preparing an LED epitaxial structure according to claim 27, characterized in that: The multi-quantum well layer is formed by alternating growth of potential well layers and potential barrier layers, wherein the material of the potential well layer includes (Al y Ga 1-y ) 0.25 In 0.25 P 0.5 , and 0.1≤y≤0.5; the material of the barrier layer includes (Al q Ga 1-q ) 0.25 In 0.25 P 0.5 , and 0.5≤q≤0.

9.

29. The method for preparing an LED epitaxial structure according to claim 28, characterized in that: The material of the first barrier layer includes (Al x Ga 1-x ) 0.25 In 0.25 P 0.5 , wherein x is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the first barrier layer is 50nm to 400nm.

30. The method for preparing an LED epitaxial structure according to claim 28, characterized in that: The material of the second barrier layer includes (Al w Ga 1-w ) 0.25 In 0.25 P 0.5 , wherein w is the same as the Al component q in the barrier layer of the multi-quantum well layer, and the thickness of the second barrier layer is 50nm to 400nm.

31. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The material of the second-type confinement layer includes AlInP, and the thickness of the second-type confinement layer is 200 nm to 600 nm.

32. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The material of the second-type current spreading layer includes GaP, the second-type current spreading layer is doped with Mg, and the thickness of the second-type current spreading layer is 500nm-3000nm.

33. The method for preparing an LED epitaxial structure according to claim 17, characterized in that: The second-type ohmic contact layer is doped with carbon, and the thickness of the second-type ohmic contact layer is 50 nm to 200 nm.

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