LED epitaxial structure and preparation method thereof
By employing U-shaped doped P-type and N-type semiconductor layers and a superlattice structure in the LED epitaxial structure, the breakdown and leakage problems caused by high electrostatic voltage in gallium nitride-based LEDs are solved, thereby improving the reliability and current expansion capability of LEDs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAMEN SILAN ADVANCED COMPOUND SEMICON CO LTD
- Filing Date
- 2023-04-24
- Publication Date
- 2026-06-16
AI Technical Summary
Gallium nitride-based light-emitting diodes are prone to high electrostatic voltage due to the accumulation of induced charges during the manufacturing process, which can lead to breakdown and leakage, affecting the reliability of the LED.
A U-shaped doped P-type and N-type semiconductor layer structure is adopted, combined with a superlattice structure of AlN layer and InxGa(1-x)N layer to improve antistatic capability, and hole injection efficiency is optimized by Mg doping.
It enhances the anti-static capability of LEDs, reduces leakage paths, improves the reliability and crystal quality of LEDs, and lowers the operating voltage.
Smart Images
Figure CN116247138B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and in particular to an LED epitaxial structure and its fabrication method. Background Technology
[0002] Gallium nitride-based light-emitting diodes (LEDs) are widely used in various light source fields such as backlighting, lighting, automotive lights, and decoration due to their high luminous efficiency.
[0003] Gallium nitride (GaN) is a wide bandgap, high resistivity material, which makes it difficult for induced charges generated during the production process to disappear. When the induced charges accumulate to a certain level, they can generate a very high electrostatic voltage, which can easily cause the light-emitting diode (LED) to break down, leading to leakage and seriously affecting the reliability of the LED.
[0004] Therefore, it is necessary to provide an LED epitaxial structure and its fabrication method to enhance the antistatic capability of LEDs, thereby improving leakage current and increasing the reliability of LEDs. Summary of the Invention
[0005] The purpose of this invention is to provide an LED epitaxial structure and its preparation method to enhance the antistatic capability of LEDs, improve the leakage current problem of LEDs, and thus improve the reliability of LEDs.
[0006] To achieve the above and other related objectives, the present invention provides an LED epitaxial structure comprising, from bottom to top: a substrate, a buffer layer, an unintentionally doped layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer, wherein the P-type semiconductor layer comprises a first P-type semiconductor layer, a second P-type semiconductor layer, and a third P-type semiconductor layer stacked sequentially, at least a portion of the structural layers in the P-type semiconductor layer are doped with Mg, and the Mg doping concentration of the second P-type semiconductor layer is less than the Mg doping concentration of the first P-type semiconductor layer and less than the Mg doping concentration of the third P-type semiconductor layer.
[0007] Optionally, in the LED epitaxial structure, the Mg doping concentration of the first P-type semiconductor layer is 5E19cm⁻¹. -3 ~5E20cm -3 The second P-type semiconductor layer is undoped or lightly doped with Mg, and the doping concentration of the lightly doped Mg is 1E17cm⁻¹. -3 ~1E19cm -3 The Mg doping concentration of the third P-type semiconductor layer is greater than 5E20cm⁻¹. -3 .
[0008] Optionally, in the LED epitaxial structure, the first P-type semiconductor layer is a superlattice structure formed by alternating growth of an AlN layer, a first Mg layer, and a first MgN layer, and the number of periods of the superlattice structure is 10 to 20.
[0009] Optionally, in the LED epitaxial structure, the thickness of the first P-type semiconductor layer is 15nm to 70nm, and the thickness of the AlN layer in each cycle is 0.7nm to 2nm, the thickness of the first Mg layer is 0.3nm to 0.5nm, and the thickness of the first MgN layer is 0.5nm to 1nm.
[0010] Optionally, in the LED epitaxial structure, the thickness of a single cycle of the AlN layer gradually decreases along the growth direction of the first P-type semiconductor layer.
[0011] Optionally, in the LED epitaxial structure, the material of the second P-type semiconductor layer includes at least one of GaN, AlGaN, and AlInGaN, and the thickness of the second P-type semiconductor layer is 20nm to 200nm.
[0012] Optionally, in the LED epitaxial structure, the third P-type semiconductor layer is In. x Ga (1-x) The superlattice structure is formed by alternating growth of N layer, second Mg layer and second MgN layer, with x ranging from 0.005 to 0.02 and the number of periods of the superlattice structure ranging from 5 to 10.
[0013] Optionally, in the LED epitaxial structure, the In x Ga (1-x) The In composition of a single cycle in the N layer gradually increases along the growth direction of the third P-type semiconductor layer.
[0014] Optionally, in the LED epitaxial structure, the thickness of the third P-type semiconductor layer is 7.5 nm to 35 nm, and the In in each cycle x Ga (1-x) The thickness of the N layer is 0.7 nm to 2 nm, the thickness of the second Mg layer is 0.3 nm to 0.5 nm, and the thickness of the second MgN layer is 0.5 nm to 1 nm.
[0015] Optionally, in the LED epitaxial structure, the In x Ga (1-x) The thickness of a single cycle of the N-layer gradually increases along the growth direction of the third P-type semiconductor layer.
[0016] Optionally, in the LED epitaxial structure, the N-type semiconductor layer includes a first N-type semiconductor layer, a second N-type semiconductor layer, and a third N-type semiconductor layer stacked sequentially. The first N-type semiconductor layer, the second N-type semiconductor layer, and the third N-type semiconductor layer are doped with Si, and the Si doping concentration of the second N-type semiconductor layer is less than the Si doping concentration of the first N-type semiconductor layer and less than the Si doping concentration of the third N-type semiconductor layer.
[0017] Optionally, in the LED epitaxial structure, the Si doping concentration of the first N-type semiconductor layer is 1E18cm⁻¹. -3 ~1E19cm -3 The Si doping concentration of the second N-type semiconductor layer is 1E17cm⁻¹. -3 ~1E18cm -3 The Si doping concentration of the third N-type semiconductor layer is 1E19cm⁻¹. -3 ~1E20cm -3 .
[0018] Optionally, in the LED epitaxial structure, the first N-type semiconductor layer is a first Si layer, a first SiN layer, and an Al layer. a Ga (1-a) The superlattice structure is formed by the sequential growth of N layers, where a ranges from 0.01 to 0.1, and the number of periods in the superlattice structure is from 5 to 10.
[0019] Optionally, in the LED epitaxial structure, the thickness of the first N-type semiconductor layer is 100nm to 500nm, and the thickness of the first Si layer in each cycle is 0.2nm to 0.5nm, the thickness of the first SiN layer is 0.3nm to 1nm, and the Al... a Ga (1-a) The thickness of the N layer ranges from 19.5 nm to 48.5 nm.
[0020] Optionally, in the LED epitaxial structure, the material of the second N-type semiconductor layer includes at least one of GaN, AlGaN, and AlInGaN, and the thickness of the second N-type semiconductor layer is 100nm to 500nm.
[0021] Optionally, in the LED epitaxial structure, the third N-type semiconductor layer is a superlattice structure formed by alternating growth of a second Si layer, a second SiN layer, and a GaN layer, and the number of periods of the superlattice structure is 10 to 20.
[0022] Optionally, in the LED epitaxial structure, the thickness of the third N-type semiconductor layer is 500nm to 2000nm, and the thickness of the second Si layer in each cycle is 0.2nm to 0.5nm, the thickness of the second SiN layer is 0.3nm to 1nm, and the thickness of the GaN layer is 49.5nm to 98.5nm.
[0023] Optionally, in the LED epitaxial structure, the LED epitaxial structure further includes an electron blocking layer, and the electron blocking layer is located between the active layer and the first P-type semiconductor layer.
[0024] Optionally, in the LED epitaxial structure, the LED epitaxial structure further includes a stress buffer layer, and the stress buffer layer is located between the N-type semiconductor layer and the active layer.
[0025] To achieve the above and other related objectives, the present invention also provides a method for fabricating an LED epitaxial structure, comprising the following steps:
[0026] Provide a substrate;
[0027] A buffer layer, an unintentionally doped layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer are sequentially grown on the substrate. The P-type semiconductor layer includes a first P-type semiconductor layer, a second P-type semiconductor layer, and a third P-type semiconductor layer stacked sequentially. At least a portion of the structural layers in the P-type semiconductor layer are doped with Mg, and the Mg doping concentration of the second P-type semiconductor layer is less than the Mg doping concentration of the first P-type semiconductor layer and less than the Mg doping concentration of the third P-type semiconductor layer.
[0028] Optionally, in the method for fabricating the LED epitaxial structure, the Mg doping concentration of the first P-type semiconductor layer is 5E19cm⁻¹. -3 ~5E20cm -3 The second P-type semiconductor layer is undoped or lightly doped with Mg, and the doping concentration of the lightly doped Mg is 1E17cm⁻¹. -3 ~1E19cm -3 The Mg doping concentration of the third P-type semiconductor layer is greater than 5E20cm⁻¹. -3 .
[0029] Optionally, in the method for preparing the LED epitaxial structure, the first P-type semiconductor layer is a superlattice structure formed by alternating growth of an AlN layer, a first Mg layer, and a first MgN layer, and the number of periods of the superlattice structure is 10 to 20.
[0030] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the first P-type semiconductor layer is 15nm to 70nm, and the thickness of the AlN layer in each cycle is 0.7nm to 2nm, the thickness of the first Mg layer is 0.3nm to 0.5nm, and the thickness of the first MgN layer is 0.5nm to 1nm.
[0031] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of a single cycle of the AlN layer gradually decreases along the growth direction of the first P-type semiconductor layer.
[0032] Optionally, in the method for preparing the LED epitaxial structure, the material of the second P-type semiconductor layer includes at least one of GaN, AlGaN, and AlInGaN, and the thickness of the second P-type semiconductor layer is 20 nm to 200 nm.
[0033] Optionally, in the method for fabricating the LED epitaxial structure, the third P-type semiconductor layer is In. x Ga (1-x) The superlattice structure is formed by alternating growth of N layer, second Mg layer and second MgN layer, with x ranging from 0.005 to 0.02 and the number of periods of the superlattice structure ranging from 5 to 10.
[0034] Optionally, in the method for fabricating the LED epitaxial structure, the In x Ga (1-x) The In composition of a single cycle in the N layer gradually increases along the growth direction of the third P-type semiconductor layer.
[0035] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the third P-type semiconductor layer is 7.5 nm to 35 nm, and the In layer in each cycle... x Ga (1-x) The thickness of the N layer is 0.7 nm to 2 nm, the thickness of the second Mg layer is 0.3 nm to 0.5 nm, and the thickness of the second MgN layer is 0.5 nm to 1 nm.
[0036] Optionally, in the method for fabricating the LED epitaxial structure, the In x Ga (1-x) The thickness of a single cycle of the N-layer gradually increases along the growth direction of the third P-type semiconductor layer.
[0037] Optionally, in the method for fabricating the LED epitaxial structure, the N-type semiconductor layer includes a first N-type semiconductor layer, a second N-type semiconductor layer, and a third N-type semiconductor layer stacked sequentially. The first N-type semiconductor layer, the second N-type semiconductor layer, and the third N-type semiconductor layer are doped with Si, and the Si doping concentration of the second N-type semiconductor layer is less than the Si doping concentration of the first N-type semiconductor layer and less than the Si doping concentration of the third N-type semiconductor layer.
[0038] Optionally, in the method for fabricating the LED epitaxial structure, the Si doping concentration of the first N-type semiconductor layer is 1E18cm⁻¹. -3 ~1E19cm -3 The Si doping concentration of the second N-type semiconductor layer is 1E17cm⁻¹. -3 ~1E18cm -3 The Si doping concentration of the third N-type semiconductor layer is 1E19cm⁻¹. -3 ~1E20cm -3 .
[0039] Optionally, in the method for fabricating the LED epitaxial structure, the first N-type semiconductor layer is a first Si layer, a first SiN layer, and an Al layer. a Ga (1-a) The superlattice structure is formed by the sequential growth of N layers, where a ranges from 0.01 to 0.1, and the number of periods in the superlattice structure is from 5 to 10.
[0040] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the first N-type semiconductor layer is 100 nm to 500 nm, and the thickness of the first Si layer in each cycle is 0.2 nm to 0.5 nm, the thickness of the first SiN layer is 0.3 nm to 1 nm, and the Al... a Ga (1-a) The thickness of the N layer ranges from 19.5 nm to 48.5 nm.
[0041] Optionally, in the method for preparing the LED epitaxial structure, the material of the second N-type semiconductor layer includes at least one of GaN, AlGaN, and AlInGaN, and the thickness of the second N-type semiconductor layer is 100nm to 500nm.
[0042] Optionally, in the method for preparing the LED epitaxial structure, the third N-type semiconductor layer is a superlattice structure formed by alternating growth of a second Si layer, a second SiN layer, and a GaN layer, and the number of periods of the superlattice structure is 10 to 20.
[0043] Optionally, in the method for fabricating the LED epitaxial structure, the thickness of the third N-type semiconductor layer is 500nm to 2000nm, and the thickness of the second Si layer in each cycle is 0.2nm to 0.5nm, the thickness of the second SiN layer is 0.3nm to 1nm, and the thickness of the GaN layer is 49.5nm to 98.5nm.
[0044] Optionally, in the method for fabricating the LED epitaxial structure, the LED epitaxial structure further includes an electron blocking layer, and the electron blocking layer is located between the active layer and the first P-type semiconductor layer.
[0045] Optionally, in the method for fabricating the LED epitaxial structure, the LED epitaxial structure further includes a stress buffer layer, and the stress buffer layer is located between the N-type semiconductor layer and the active layer.
[0046] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:
[0047] This invention configures the P-type semiconductor layer as a first P-type semiconductor layer, a second P-type semiconductor layer, and a third P-type semiconductor layer stacked sequentially, with the Mg doping concentration of the second P-type semiconductor layer < the Mg doping concentration of the first P-type semiconductor layer < the Mg doping concentration of the third P-type semiconductor layer. This invention creates a "U"-shaped doped P-type semiconductor layer. The "U"-shaped doping structure resembles a parallel-plate capacitor, exhibiting capacitor-like characteristics and improving electrostatic discharge (ESD) immunity. Furthermore, the relatively low Mg doping concentration of the second P-type semiconductor layer increases current spread, prevents current accumulation, and avoids leakage channels, further enhancing ESD immunity. Simultaneously, it improves the crystal quality of the LED epitaxial structure, resulting in fewer defects and leakage channels, higher ESD immunity, and ultimately improving LED leakage problems and reliability.
[0048] Secondly, this invention configures the N-type semiconductor layer as a first N-type semiconductor layer, a second N-type semiconductor layer, and a third N-type semiconductor layer stacked sequentially, with the Si doping concentration of the second N-type semiconductor layer < the Si doping concentration of the first N-type semiconductor layer < the Si doping concentration of the third N-type semiconductor layer. That is, this invention configures a "U"-shaped doped N-type semiconductor layer. The "U"-shaped doping structure is similar to forming a parallel-plate capacitor, exhibiting capacitor-like characteristics and improving anti-static capability. Furthermore, the relatively low Si doping concentration of the second N-type semiconductor layer increases current spread capability, avoids current accumulation, prevents leakage channels, and improves anti-static capability. Simultaneously, it also improves the crystal quality of the LED epitaxial structure, resulting in fewer defects and leakage channels, higher anti-static capability, and thus improving the leakage problem and reliability of the LED.
[0049] Moreover, the first P-type semiconductor layer of the present invention is a superlattice structure formed by alternating growth of AlN layer, first Mg layer and first MgN layer, which can alleviate the stress between the electron blocking layer and the second P-type semiconductor layer. The AlN layer uses AlN material with a high bandgap, and its gradually decreasing thickness is more conducive to the movement of holes from the P-type semiconductor layer to the active layer. The superlattice structure composed of AlN layer, first Mg layer and first MgN layer provides highly doped Mg, which is conducive to Mg ionization to generate more holes, improve hole injection efficiency and enhance radiative recombination luminescence.
[0050] Furthermore, the third P-type semiconductor layer of the present invention is In. x Ga (1-x) A superlattice structure formed by alternating N-layer, second Mg-layer, and second MgN-layer, along with the growth direction of the third P-type semiconductor layer, is formed. x Ga (1-x) The thickness of layer N gradually increases, and In x Ga (1-x) The In content of the N layer also gradually increases. The In content can reduce the activation energy of Mg. The increase in In content makes it easier to form high doping and obtain better ohmic contacts, which reduces the operating voltage of the LED. Attached Figure Description
[0051] Figure 1 A schematic diagram of an LED epitaxial structure according to an embodiment of the present invention is shown;
[0052] Figure 2 A schematic diagram of the structure of an N-type semiconductor layer according to an embodiment of the present invention is shown;
[0053] Figure 3 A schematic diagram of the structure of a P-type semiconductor layer according to an embodiment of the present invention is shown;
[0054] Figure 4 The secondary ion mass spectrum of an LED epitaxial structure according to an embodiment of the present invention is shown.
[0055] in, Figures 1-4 middle:
[0056] 10-Substrate, 11-Buffer layer, 12-Unintentionally doped layer, 13-First N-type semiconductor layer, 131-First Si layer, 132-First SiN layer, 133-Al a Ga (1-a)N-layer, 14-Second N-type semiconductor layer, 15-Third N-type semiconductor layer, 151-Second Si layer, 152-Second SiN layer, 153-GaN layer, 16-Stress buffer layer, 17-Active layer, 18-Electron blocking layer, 19-First P-type semiconductor layer, 191-AlN layer, 192-First Mg layer, 193-First MgN layer, 20-Second P-type semiconductor layer, 21-Third P-type semiconductor layer, 211-In x Ga (1-x) N layer, 212-second Mg layer, 213-second MgN layer. Detailed Implementation
[0057] The LED epitaxial structure and its fabrication method proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.
[0058] Before describing embodiments according to the present invention, the following points will be explained in advance. First, in this specification, when referred to only as "AlInGaN", it indicates an arbitrary compound in which the chemical composition ratio of the sum of Al, Ga, and In to N is 1:1, and the ratio of Al, Ga, and In is not fixed. Similarly, when referred to only as "AlGaN", it indicates an arbitrary compound in which the chemical composition ratio of the sum of Al, Ga, and N is 1:1, and the ratio of Al to Ga is not fixed. And when referred to only as "InGaN", it indicates an arbitrary compound in which the chemical composition ratio of the sum of In, Ga, and N is 1:1, and the ratio of In to Ga is not fixed.
[0059] See Figure 1 The LED epitaxial structure, from bottom to top, includes: a substrate 10, a buffer layer 11, an unintentionally doped layer 12, an N-type semiconductor layer, an active layer 17, and a P-type semiconductor layer.
[0060] The N-type semiconductor layer may include a first N-type semiconductor layer 13, a second N-type semiconductor layer 14, and a third N-type semiconductor layer 15 stacked sequentially. The first N-type semiconductor layer 13, the second N-type semiconductor layer 14, and the third N-type semiconductor layer 15 are doped with Si, and the Si doping concentration of the second N-type semiconductor layer 14 is less than the Si doping concentration of the first N-type semiconductor layer 13, which is less than the Si doping concentration of the third N-type semiconductor layer 15. That is, the present invention provides a U-shaped doped N-type semiconductor layer. The U-shaped doping structure is similar to forming a parallel-plate capacitor, exhibiting capacitor-like characteristics, which can improve the anti-static capability of the LED, alleviate the leakage current problem of the LED, and enhance the reliability of the LED.
[0061] See Figure 2 The first N-type semiconductor layer 13 is a first Si layer 131, a first SiN layer 132, and an Al layer 133. a Ga (1-a) The superlattice structure formed by the sequential alternating growth of N layers 133 has an a value preferably ranging from 0.01 to 0.1. In this embodiment, the first Si layer 131 and the first SiN layer 132 can preferentially fill dislocations and defects, while Al... a Ga (1-a) The N-layer 133 can prevent dislocation propagation and change the direction of dislocation propagation. Furthermore, the highly doped superlattice structure adopted by the first N-type semiconductor layer 13 can increase the current spread capability and improve the antistatic capability of the LED.
[0062] The material of the second N-type semiconductor layer 14 includes at least one of GaN, AlGaN, and AlInGaN. Furthermore, the Si doping concentration of the second N-type semiconductor layer 14 is lower than that of the first N-type semiconductor layer 13 and the third N-type semiconductor layer 15, to form a U-shaped doped N-type semiconductor layer.
[0063] Continue reading Figure 2 The third N-type semiconductor layer 15 is a superlattice structure formed by alternating growth of a second Si layer 151, a second SiN layer 152, and a GaN layer 153. The second Si layer 151 and the second SiN layer 152 preferentially fill dislocations and defects, which helps to reduce dislocation density and improve crystal quality. Furthermore, the highly doped superlattice structure of the third N-type semiconductor layer 15 can also increase current spreading capability and improve the LED's anti-static capability.
[0064] The P-type semiconductor layer may include a first P-type semiconductor layer 19, a second P-type semiconductor layer 20, and a third P-type semiconductor layer 21 stacked sequentially, wherein the Mg doping concentration of the second P-type semiconductor layer 20 is less than the Mg doping concentration of the first P-type semiconductor layer 19, and the Mg doping concentration of the third P-type semiconductor layer 21. That is, the present invention provides a "U"-shaped doped P-type semiconductor layer. The "U"-shaped doping structure is similar to forming a parallel-plate capacitor, exhibiting capacitor-like characteristics, which can improve the anti-static capability of the LED, alleviate the leakage current problem of the LED, and thus improve the reliability of the LED.
[0065] See Figure 3The first P-type semiconductor layer 19 can be a superlattice structure formed by alternating growth of AlN layer 191, first Mg layer 192, and first MgN layer 193. This superlattice structure can alleviate the stress between the electron blocking layer 18 and the second P-type semiconductor layer 20. The AlN layer 191 is made of AlN, a material with a high bandgap, and its gradually decreasing thickness is more conducive to the movement of holes from the P-type semiconductor layer to the active layer 17. Furthermore, the superlattice composed of AlN layer 191, first Mg layer 192, and first MgN layer 193 provides highly doped Mg, which is conducive to Mg ionization to generate more holes, improves hole injection efficiency, and enhances radiative recombination luminescence.
[0066] The material of the second P-type semiconductor layer 20 may include at least one of GaN, AlGaN, and AlInGaN. Compared to the first P-type semiconductor layer 19 and the third P-type semiconductor layer 21, the second P-type semiconductor layer 20 has a lower Mg doping concentration to form a U-shaped doped P-type semiconductor layer. Furthermore, the lower Mg doping concentration of the second P-type semiconductor layer increases current spreading capability, avoids current accumulation, prevents leakage channels, and improves electrostatic discharge (ESD) immunity. It also improves the crystal quality of the LED epitaxial structure, resulting in fewer defects and leakage channels, higher ESD immunity, and thus improving LED leakage current and reliability.
[0067] Continue reading Figure 3 The third P-type semiconductor layer 21 is In x Ga (1-x) The superlattice structure formed by the alternating growth of N-layer 211, second Mg-layer 212, and second MgN-layer 213, preferably has x in the range of 0.005 to 0.02. In this embodiment, along the growth direction of the third P-type semiconductor layer 21, the In... x Ga (1-x) The thickness of a single cycle of N-layer 211 preferably increases gradually, while the In x Ga (1-x) The In content of a single cycle in layer N211 is also preferably gradually increased. For example, the In... x Ga (1-x) The thickness and In composition of the second cycle of N-layer 211 are greater than those of the first cycle. The In... x Ga (1-x) The In composition of the N-layer 211 can reduce the activation energy of Mg. A higher In composition makes it easier to form high doping and obtain better ohmic contacts, thus reducing the operating voltage of the LED.
[0068] The LED epitaxial structure of this embodiment may further include a stress buffer layer 16, and the stress buffer layer 16 is located between the N-type semiconductor layer and the active layer 17. More specifically, the stress buffer layer 16 is located between the third N-type semiconductor layer 15 and the active layer 17.
[0069] The LED epitaxial structure of this embodiment may further include an electron blocking layer 18, and the electron blocking layer 18 is located between the active layer 17 and the P-type semiconductor layer. More specifically, the electron blocking layer 18 is located between the active layer 17 and the first P-type semiconductor layer 19.
[0070] The method for preparing the LED epitaxial structure specifically includes the following steps:
[0071] Step S1: Provide a substrate 10;
[0072] Step S2: A buffer layer 11, an unintentionally doped layer 12, an N-type semiconductor layer, an active layer 17, and a P-type semiconductor layer are sequentially grown on the substrate 10. The P-type semiconductor layer includes a first P-type semiconductor layer 19, a second P-type semiconductor layer 20, and a third P-type semiconductor layer 21 stacked sequentially. At least a portion of the structural layers in the P-type semiconductor layer are doped with Mg, and the Mg doping concentration of the second P-type semiconductor layer 20 is less than the Mg doping concentration of the first P-type semiconductor layer 19 and less than the Mg doping concentration of the third P-type semiconductor layer 21.
[0073] The fabrication process of the LED epitaxial structure can be any one of MOCVD, molecular beam epitaxy, HVPE, plasma-assisted chemical vapor deposition, and sputtering, with MOCVD being preferred. The following specific embodiments use MOCVD as an example for illustration.
[0074] Step S1 is performed to provide the substrate 10. As the substrate 10, it is preferable to use a substrate that can transmit light emitted by the active layer 17 and emit light from the substrate side. For example, a sapphire substrate or a single-crystal AlN substrate can be used, and a patterned sapphire substrate is preferred.
[0075] Step S2 is performed to grow a buffer layer 11 on the substrate 10. The buffer layer 11 is adjacent to the substrate 10 and can reduce defects and dislocations in the epitaxial structure caused by surface defects of the substrate 10 or by lattice mismatch or thermal mismatch between the substrate 10 and the epitaxial structure, and provides a high-quality growth surface for the structural layer above the buffer layer 11. The material of the buffer layer 11 is preferably at least one of GaN, AlN, and AlGaN, but is not limited thereto. The thickness of the buffer layer 11 is preferably 10 nm to 20 nm, for example, 20 nm.
[0076] In step S2, after growing the buffer layer 11, an unintentionally doped layer 12 is grown on the buffer layer 11 to optimize growth and obtain a high-quality crystal. The unintentionally doped layer 12 can also serve as a roughening layer for vertical chip processing. In this embodiment, the material of the unintentionally doped layer 12 is preferably GaN, but it is not limited thereto. The thickness of the unintentionally doped layer 12 is preferably 2μm to 5μm, for example, 3μm.
[0077] After the step of growing the unintentionally doped layer 12, an N-type semiconductor layer is grown on the unintentionally doped layer 12. The N-type semiconductor layer includes a first N-type semiconductor layer 13, a second N-type semiconductor layer 14, and a third N-type semiconductor layer 15 stacked sequentially. Therefore, after the step of growing the unintentionally doped layer 12, the first N-type semiconductor layer 13 is grown on the unintentionally doped layer 12.
[0078] The first N-type semiconductor layer 13 is doped with Si, and the Si doping concentration is preferably 1E18cm⁻¹. -3 ~1E19cm -3 This embodiment can obtain data on each component in the first N-type semiconductor layer 13 through SIMS (Secondary Ion Mass Spectrometry) testing, as detailed in the following reference. Figure 4 For example, the concentration of Si in the first N-type semiconductor layer 13 is obtained by SIMS testing.
[0079] The first N-type semiconductor layer 13 can be a first Si layer 131, a first SiN layer 132, and an Al layer. a Ga (1-a) The superlattice structure formed by the sequential alternating growth of N layers 133 has a preferred range of 0.01 to 0.1, and the number of periods of the superlattice structure is preferably 5 to 10.
[0080] The overall thickness of the first N-type semiconductor layer 13 is preferably 100 nm to 500 nm. The first Si layer 131 can be a single-atom layer of Si, and the thickness of the first Si layer 131 in each period is preferably 0.2 nm to 0.5 nm, for example, 0.3 nm. The material of the first SiN layer 132 is preferably SiN, and the thickness of the first SiN layer 132 in each period is preferably 0.3 nm to 1 nm, for example, 0.5 nm. The Al... a Ga (1-a) The material of layer N133 is preferably Al. a Ga (1-a) N,a is preferably in the range of 0.01 to 0.1, and the Al in each cycle a Ga (1-a) The thickness of the N layer 133 is preferably 19.5 nm to 48.5 nm, for example 40 nm.
[0081] After growing the first N-type semiconductor layer 13, the second N-type semiconductor layer 14 is grown. The second N-type semiconductor layer 14 is doped with Si, and the Si doping concentration of the second N-type semiconductor layer 14 is lower than the Si doping concentration of the first N-type semiconductor layer 13, and also lower than the Si doping concentration of the third N-type semiconductor layer 15, to form a U-shaped doped N-type semiconductor layer. Further, the Si doping concentration of the second N-type semiconductor layer 14 is preferably 1E17cm⁻¹. -3 ~1E18cm -3 This embodiment can obtain data on each component in the second N-type semiconductor layer 14 through SIMS testing, as detailed in the following reference. Figure 4 For example, the concentration of Si in the second N-type semiconductor layer 14 is obtained by SIMS testing.
[0082] In this embodiment, the material of the second N-type semiconductor layer 14 is preferably at least one of GaN, AlGaN, and AlInGaN, but is not limited thereto. The thickness of the second N-type semiconductor layer 14 is preferably 100 nm to 500 nm, for example, 400 nm.
[0083] After the step of growing the second N-type semiconductor layer 14, the third N-type semiconductor layer 15 is grown on the second N-type semiconductor layer 14. The third N-type semiconductor layer 15 is used to form an ohmic contact with the N-electrode metal. The third N-type semiconductor layer 15 can be a superlattice structure formed by sequentially growing a second Si layer 151, a second SiN layer 152, and a GaN layer 153, and the number of periods of the superlattice structure is preferably 10 to 20.
[0084] The third N-type semiconductor layer 15 is doped with Si, and the Si doping concentration of the third N-type semiconductor layer 15 is greater than the Si doping concentration of the first N-type semiconductor layer 13. Furthermore, the Si doping concentration of the third N-type semiconductor layer 15 is preferably 1E19cm⁻¹. -3 ~1E20cm -3 The third N-type semiconductor layer 15 serves as an N-type ohmic contact layer, and a higher Si doping concentration is beneficial for forming ohmic contacts, which can reduce the operating voltage of the LED. In this embodiment, data on each component in the third N-type semiconductor layer 15 can be obtained through SIMS testing; please refer to [reference needed]. Figure 4 For example, the concentration of Si in the third N-type semiconductor layer 15 is obtained by SIMS testing.
[0085] The overall thickness of the third N-type semiconductor layer 15 is preferably 500 nm to 2000 nm. The second Si layer 151 can be a single-atom layer of Si, and the thickness of the second Si layer 151 in each period is preferably 0.2 nm to 0.5 nm, for example, 0.3 nm. The material of the second SiN layer 152 is preferably SiN, and the thickness of the second SiN layer 152 in each period is preferably 0.3 nm to 1 nm, for example, 0.5 nm. The material of the GaN layer 153 is preferably GaN, and the thickness of the GaN layer 153 in each period is preferably 49.5 nm to 98.5 nm, for example, 50 nm.
[0086] In this embodiment, by setting the Si doping concentration of the second N-type semiconductor layer 14 to be less than the Si doping concentration of the first N-type semiconductor layer 13 to be less than the Si doping concentration of the third N-type semiconductor layer 15, the N-type semiconductor layer is configured with a "U"-shaped doping, which can improve the antistatic capability of the LED, and also enhance the current spreading capability and ohmic contact capability.
[0087] In this embodiment, the LED epitaxial structure may further include the stress buffer layer 16, and the stress buffer layer 16 is located between the N-type semiconductor layer and the active layer 17. More specifically, the stress buffer layer 16 is located between the third N-type semiconductor layer 15 and the active layer 17. Therefore, after the step of growing the third N-type semiconductor layer 15, the stress buffer layer 16 is grown on the third N-type semiconductor layer 15.
[0088] In this embodiment, the stress buffer layer 16 can be a GaN structure layer, a structure layer composed of InGaN and GaN (e.g., a superlattice structure composed of InGaN and GaN), a structure layer composed of InGaN and AlGaN (e.g., a superlattice structure composed of InGaN and AlGaN), or a combination of any two of the above structure layers. The stress buffer layer 16 helps to alleviate stress in the epitaxial structure, improves the stress balance of the active layer 17, and enhances the crystal quality of the active layer 17.
[0089] After the step of growing the stress buffer layer 16, an active layer 17 is grown on the stress buffer layer 16. In this embodiment, the active layer 17 is preferably a multi-quantum-well structure, and the multi-quantum-well structure can be one of, but is not limited to, a superlattice structure composed of InGaN and GaN, a superlattice structure composed of InGaN and AlGaN, or a superlattice structure composed of AlInGaN and AlInGaN. Electrons and holes in the active layer 17 undergo radiative recombination. With preferred growth conditions, an active layer 17 with high crystal quality can be obtained, reducing ineffective recombination caused by defects, etc.
[0090] In this embodiment, the LED epitaxial structure may further include the electron blocking layer 18, and the electron blocking layer 18 is located between the active layer 17 and the P-type semiconductor layer. Specifically, the electron blocking layer 18 is located between the active layer 17 and the first P-type semiconductor layer 19. Therefore, after the step of growing the active layer 17, the electron blocking layer 18 is grown on the active layer 17.
[0091] In this embodiment, the electron blocking layer 18 is preferably made of at least one of AlGaN, AlInGaN, AlN, and GaN. The electron blocking layer 18 prevents electrons from overflowing into the P-type semiconductor layer, reducing the impact on LED performance.
[0092] After the step of growing the electron blocking layer 18, a P-type semiconductor layer is grown on the electron blocking layer 18. In this embodiment, the P-type semiconductor layer includes a first P-type semiconductor layer 19, a second P-type semiconductor layer 20, and a third P-type semiconductor layer 21 stacked sequentially. Therefore, after the step of growing the electron blocking layer 18, the first P-type semiconductor layer 19 is grown on the electron blocking layer 18.
[0093] The first P-type semiconductor layer 19 can be a superlattice structure formed by alternating growth of an AlN layer 191, a first Mg layer 192, and a first MgN layer 193, and the number of periods in the superlattice structure is preferably 10 to 20. The first P-type semiconductor layer 19 is doped with Mg, and the Mg single-atom layer of the first Mg layer 192 has a small size, preferentially filling defect sites during growth, thus improving crystal quality. Furthermore, due to the diffusion and memory effect of Mg, the overall Mg doping concentration of the superlattice structure layer of the first P-type semiconductor layer 19 is preferably 5E19cm⁻¹. -3 ~5E20cm -3 This embodiment can obtain data on each component in the first P-type semiconductor layer 19 through SIMS testing, as detailed in the following reference. Figure 4 For example, the concentration of Mg in the first P-type semiconductor layer 19 is obtained by SIMS testing.
[0094] In this embodiment, the AlN layer 191 helps to alleviate the stress between the electron blocking layer 18 and the second P-type semiconductor layer 20, thereby improving polarization. The first Mg layer 192 preferentially fills the defect sites during the growth of a single atomic layer, and together with the first MgN layer 193, it plays a role in improving defects and improving crystal quality. In addition, the relatively high doping concentration of the first P-type semiconductor layer 19 helps to increase the current spreading capability.
[0095] The overall thickness of the first P-type semiconductor layer 19 is preferably 15 nm to 70 nm. The material of the AlN layer 191 is preferably AlN, and the thickness of the AlN layer 191 in each cycle is preferably 0.7 nm to 2 nm, for example, 1 nm. Furthermore, the thickness of the AlN layer 191 in a single cycle preferably gradually decreases along the growth direction of the first P-type semiconductor layer 19, which facilitates hole injection into the active layer 17. For example, the thickness of the first cycle of the AlN layer 191 is greater than the thickness of the second cycle of the AlN layer 191. The first Mg layer 192 is a single-atom Mg layer, and the thickness of the first Mg layer 192 in each cycle is preferably 0.3 nm to 0.5 nm, for example, 0.5 nm. The material of the first MgN layer 193 is preferably MgN, and the thickness of the first MgN layer 193 in each cycle is preferably 0.5 nm to 1 nm, for example, 0.8 nm.
[0096] After growing the first P-type semiconductor layer 19, a second P-type semiconductor layer 20 is grown on the first P-type semiconductor layer 19. The material of the second P-type semiconductor layer 20 includes at least one of GaN, AlGaN, and AlInGaN, but is not limited thereto. To fill small defects or surface irregularities formed during the epitaxial growth process and obtain a smooth and flat epitaxial structure surface, the thickness of the second P-type semiconductor layer 20 in this embodiment is preferably 20 nm to 200 nm. To ensure good current spreading capability of the P-type semiconductor layer, the second P-type semiconductor layer 20 is undoped or lightly doped with Mg, and the doping concentration of the lightly doped Mg is preferably 1E17 cm⁻¹. -3 ~1E19cm -3 .
[0097] This embodiment can obtain data on each component in the second P-type semiconductor layer 20 through SIMS testing, which can be referred to as... Figure 4 For example, the concentration of Mg in the second P-type semiconductor layer 20 can be obtained by SIMS testing.
[0098] After the step of growing the second P-type semiconductor layer 20, a third P-type semiconductor layer 21 is grown on the second P-type semiconductor layer 20. The third P-type semiconductor layer 21 is used to form a good ohmic contact with the P-electrode metal. The third P-type semiconductor layer 21 can be In... x Ga (1-x) The superlattice structure is formed by the alternating growth of N layer 211, second Mg layer 212 and second MgN layer 213, and the number of periods of the superlattice structure is preferably 5 to 10.
[0099] The third P-type semiconductor layer 21 is doped with Mg, and the Mg doping concentration of the third P-type semiconductor layer 21 is preferably greater than that of the first P-type semiconductor layer 19. The relatively high doping concentration of the third P-type semiconductor layer 21 helps to increase current spreading capability and improve antistatic capability. Due to the diffusion and memory effect of Mg, the overall Mg doping concentration of the superlattice structure layer of the third P-type semiconductor layer 21 is preferably greater than 5E20cm⁻¹. -3 The third P-type semiconductor layer 21 serves as a P-type ohmic contact layer, connecting to the P-electrode metal. A higher doping concentration facilitates the formation of an ohmic contact, reducing the operating voltage of the LED. In this embodiment, data on each component in the third P-type semiconductor layer 21 can be obtained through SIMS testing; please refer to [reference needed]. Figure 4 For example, the concentration of Mg in the third P-type semiconductor layer 21 can be obtained by SIMS testing.
[0100] The thickness of the third P-type semiconductor layer 21 is preferably 7.5 nm to 35 nm. The In... x Ga (1-x) The material of layer N211 is preferably In. x Ga (1-x) The preferred range for N,x is 0.005 to 0.02, and the In in each period x Ga (1-x) The thickness of the N-layer 211 is preferably 0.7 nm to 2 nm, for example, 1 nm. The In... x Ga (1-x) The In in the N-layer 211 can lower the activation energy of Mg and increase the doping concentration. Simultaneously, the highly doped third P-type semiconductor layer 21 facilitates current spread, and In... x Ga (1-x) The relatively small bandgap of the N-layer 211 facilitates the formation of ohmic contacts and reduces the operating voltage of the LED. Furthermore, the In... x Ga (1-x) The thickness of a single cycle of the N-layer 211 preferably increases gradually along the growth direction of the third P-type semiconductor layer 21, for example, the In... x Ga (1-x) The thickness of the second cycle in layer N211 is greater than the thickness of the first cycle. The In... x Ga (1-x) The thicker the N-layer 211, the lower the operating voltage of the LED, and it also better fills in defects and the slightly rough surface formed by the second Mg layer 212 and the second MgN layer 213. Furthermore, the In... x Ga (1-x) The In composition of a single cycle of the N-layer 211 preferably increases gradually along the growth direction of the third P-type semiconductor layer 21. For example, the In x Ga(1-x) The In component of the second cycle in layer N211 is larger than the In component of the first cycle. The In... x Ga (1-x) The In composition of the N-layer 211 can reduce the activation energy of Mg, increase the doping concentration, and thus improve the current spread capability. Furthermore, the gradual increase of the In composition makes it easier to form high doping and obtain better ohmic contacts, thereby reducing the operating voltage of the LED.
[0101] The second Mg layer 212 is a single Mg atom layer, and the thickness of the second Mg layer 212 in each period is preferably 0.3 nm to 0.5 nm, for example, 0.4 nm. The small size of the single Mg atom layer of the second Mg layer 212 allows it to preferentially fill defect sites during growth, and together with the second MgN layer 213, it plays a role in improving defects and enhancing crystal quality. In addition, the high doping concentration of the second Mg layer 212 and the second MgN layer 213 helps to increase current spreading capability and forms a slightly roughened surface in the superlattice, increasing light extraction.
[0102] The material of the second MgN layer 213 is preferably MgN, and the thickness of the second MgN layer 213 in each cycle is preferably 0.5 nm to 1 nm, for example 0.8 nm.
[0103] In summary, this invention configures the P-type semiconductor layers as a first P-type semiconductor layer, a second P-type semiconductor layer, and a third P-type semiconductor layer stacked sequentially, with the Mg doping concentration of the second P-type semiconductor layer < the Mg doping concentration of the first P-type semiconductor layer < the Mg doping concentration of the third P-type semiconductor layer. That is, this invention forms a capacitor-like characteristic by setting a "U"-shaped doped P-type semiconductor layer, which enhances current spreading capability, prevents LED breakdown caused by high voltage induced charge, improves the LED's anti-static capability, and enhances the LED's reliability. Furthermore, the relatively low Mg doping concentration of the second P-type semiconductor layer in this invention increases current spreading capability, avoids current accumulation, prevents the formation of leakage channels, improves anti-static capability, and also improves the crystal quality of the LED epitaxial structure, resulting in fewer defects, fewer leakage channels, and higher anti-static capability.
[0104] Secondly, this invention configures the N-type semiconductor layers as a series of sequentially stacked first, second, and third N-type semiconductor layers, with the Si doping concentration of the second N-type semiconductor layer < the Si doping concentration of the first N-type semiconductor layer < the Si doping concentration of the third N-type semiconductor layer. This means that by setting a "U"-shaped doped N-type semiconductor layer, the invention forms a capacitor-like characteristic, enhancing current spread capability, preventing LED breakdown caused by high voltage induced charges, improving the LED's anti-static capability, and increasing its reliability. Furthermore, the relatively low Si doping concentration of the second N-type semiconductor layer in this invention increases current spread capability, avoids current accumulation, prevents leakage channels, and improves anti-static capability. Simultaneously, it also improves the crystal quality of the LED epitaxial structure, resulting in fewer defects, fewer leakage channels, and higher anti-static capability.
[0105] Moreover, the first P-type semiconductor layer of the present invention is a superlattice structure formed by alternating growth of AlN layer, first Mg layer and first MgN layer, which can alleviate the stress between the electron blocking layer and the second P-type semiconductor layer. The AlN layer uses AlN material with a high bandgap, and its gradually decreasing thickness is more conducive to the movement of holes from the P-type semiconductor layer to the active layer. The superlattice composed of AlN layer, first Mg layer and first MgN layer provides highly doped Mg, which is conducive to Mg ionization to generate more holes, improve hole injection efficiency and enhance radiative recombination luminescence.
[0106] Furthermore, the third P-type semiconductor layer of the present invention is In. x Ga (1-x) A superlattice structure formed by alternating N-layer, second Mg-layer, and second MgN-layer, with In along the growth direction of the third P-type semiconductor layer. x Ga (1-x) The thickness of layer N gradually increases, and In x Ga (1-x) The In content of the N layer also gradually increases. The In content can reduce the activation energy of Mg, and the gradual increase in In content makes it easier to form high doping, obtain better ohmic contacts, and reduce the operating voltage of the LED.
[0107] It is understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the protection scope of the present invention.
[0108] Furthermore, it should be understood that the invention is not limited to the specific methods, compounds, materials, manufacturing techniques, uses, and applications described herein, which can vary. It should also be understood that the terminology described herein is used only to describe particular embodiments and not to limit the scope of the invention. It must be noted that the singular forms “a,” “an,” and “the” used herein and in the appended claims include plural bases unless the context clearly indicates otherwise. 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 logical “or” rather than logical “exclusive”, unless the context clearly indicates otherwise. Structures described herein will be understood to also refer to functional equivalents of that structure. Language that can be interpreted as approximate should be understood in that way unless the context clearly indicates otherwise.
Claims
1. An LED epitaxial structure, characterized in that, From bottom to top, the structure includes: a substrate, a buffer layer, an unintentionally doped layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer. The P-type semiconductor layer includes a first P-type semiconductor layer, a second P-type semiconductor layer, and a third P-type semiconductor layer stacked sequentially. At least a portion of the structural layers in the P-type semiconductor layer are doped with Mg, and the Mg doping concentration of the second P-type semiconductor layer is less than the Mg doping concentration of the first P-type semiconductor layer, which is less than the Mg doping concentration of the third P-type semiconductor layer. The first P-type semiconductor layer is a superlattice structure formed by alternating growth of an AlN layer, a first Mg layer, and a first MgN layer.
2. The LED epitaxial structure as described in claim 1, characterized in that, The Mg doping concentration of the first P-type semiconductor layer is 5E19cm⁻¹ -3 ~5E20cm -3 The second p-type semiconductor layer is undoped or lightly doped with Mg, and the doping concentration of the lightly doped Mg is 1E17 cm⁻¹. -3 ~1E19 cm -3 The Mg doping concentration of the third P-type semiconductor layer is greater than 5E20 cm⁻¹. -3 .
3. The LED epitaxial structure as described in claim 1, characterized in that, The number of periods in the superlattice structure of the first P-type semiconductor layer is 10 to 20.
4. The LED epitaxial structure as described in claim 3, characterized in that, The thickness of the first P-type semiconductor layer is 15nm~70nm, and the thickness of the AlN layer in each cycle is 0.7nm~2nm, the thickness of the first Mg layer is 0.3nm~0.5nm, and the thickness of the first MgN layer is 0.5nm~1nm.
5. The LED epitaxial structure as described in claim 3, characterized in that, The thickness of a single cycle of the AlN layer gradually decreases along the growth direction of the first P-type semiconductor layer.
6. The LED epitaxial structure as described in claim 1, characterized in that, The material of the second P-type semiconductor layer includes at least one of GaN, AlGaN and AlInGaN, and the thickness of the second P-type semiconductor layer is 20nm~200nm.
7. The LED epitaxial structure as described in claim 1, characterized in that, The third P-type semiconductor layer is In x Ga (1-x) The superlattice structure is formed by alternating growth of N layer, second Mg layer and second MgN layer, with x ranging from 0.005 to 0.02 and the number of periods of the superlattice structure ranging from 5 to 10.
8. The LED epitaxial structure as described in claim 7, characterized in that, The In x Ga (1-x) The In composition of a single cycle in the N layer gradually increases along the growth direction of the third P-type semiconductor layer.
9. The LED epitaxial structure as described in claim 7, characterized in that, The thickness of the third P-type semiconductor layer is 7.5 nm to 35 nm, and the In in each cycle x Ga (1-x) The thickness of the N layer is 0.7 nm to 2 nm, the thickness of the second Mg layer is 0.3 nm to 0.5 nm, and the thickness of the second MgN layer is 0.5 nm to 1 nm.
10. The LED epitaxial structure as described in claim 7, characterized in that, The In x Ga (1-x) The thickness of a single cycle of the N-layer gradually increases along the growth direction of the third P-type semiconductor layer.
11. The LED epitaxial structure as described in claim 1, characterized in that, The N-type semiconductor layer includes a first N-type semiconductor layer, a second N-type semiconductor layer, and a third N-type semiconductor layer stacked sequentially. The first N-type semiconductor layer, the second N-type semiconductor layer, and the third N-type semiconductor layer are doped with Si, and the Si doping concentration of the second N-type semiconductor layer is less than the Si doping concentration of the first N-type semiconductor layer and less than the Si doping concentration of the third N-type semiconductor layer.
12. The LED epitaxial structure as described in claim 11, characterized in that, The Si doping concentration of the first N-type semiconductor layer is 1E18cm⁻¹ -3 ~1E19cm -3 The Si doping concentration of the second N-type semiconductor layer is 1E17 cm⁻¹. -3 ~1E18 cm -3 The Si doping concentration of the third N-type semiconductor layer is 1E19 cm⁻¹. -3 ~1E20 cm -3 .
13. The LED epitaxial structure as described in claim 11, characterized in that, The first N-type semiconductor layer is a first Si layer, a first SiN layer, and an Al layer. a Ga (1-a) The superlattice structure is formed by the sequential growth of N layers, where a ranges from 0.01 to 0.1, and the number of periods in the superlattice structure is from 5 to 10.
14. The LED epitaxial structure as described in claim 13, characterized in that, The thickness of the first N-type semiconductor layer is 100nm~500nm, and the thickness of the first Si layer in each period is 0.2nm~0.5nm, the thickness of the first SiN layer is 0.3nm~1nm, and the Al... a Ga (1-a) The thickness of the N layer ranges from 19.5 nm to 48.5 nm.
15. The LED epitaxial structure as described in claim 11, characterized in that, The material of the second N-type semiconductor layer includes at least one of GaN, AlGaN and AlInGaN, and the thickness of the second N-type semiconductor layer is 100nm~500nm.
16. The LED epitaxial structure as described in claim 11, characterized in that, The third N-type semiconductor layer is a superlattice structure formed by alternating growth of the second Si layer, the second SiN layer and the GaN layer, and the number of periods of the superlattice structure is 10 to 20.
17. The LED epitaxial structure as described in claim 16, characterized in that, The thickness of the third N-type semiconductor layer is 500nm~2000nm, and the thickness of the second Si layer in each cycle is 0.2nm~0.5nm, the thickness of the second SiN layer is 0.3nm~1nm, and the thickness of the GaN layer is 49.5nm~98.5nm.
18. The LED epitaxial structure as described in claim 1, characterized in that, The LED epitaxial structure further includes an electron blocking layer, which is located between the active layer and the first P-type semiconductor layer.
19. The LED epitaxial structure as described in claim 1, characterized in that, The LED epitaxial structure further includes a stress buffer layer, which is located between the N-type semiconductor layer and the active layer.
20. A method for fabricating an LED epitaxial structure, characterized in that, Includes the following steps: Provide a substrate; A buffer layer, an unintentionally doped layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer are sequentially grown on the substrate. The P-type semiconductor layer includes a first P-type semiconductor layer, a second P-type semiconductor layer, and a third P-type semiconductor layer stacked sequentially. At least a portion of the structural layers in the P-type semiconductor layer are doped with Mg, and the Mg doping concentration of the second P-type semiconductor layer is less than the Mg doping concentration of the first P-type semiconductor layer, which is less than the Mg doping concentration of the third P-type semiconductor layer. The first P-type semiconductor layer is a superlattice structure formed by alternating growth of an AlN layer, a first Mg layer, and a first MgN layer.
21. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The Mg doping concentration of the first P-type semiconductor layer is 5E19cm⁻¹ -3 ~5E20cm -3 The second p-type semiconductor layer is undoped or lightly doped with Mg, and the doping concentration of the lightly doped Mg is 1E17 cm⁻¹. -3 ~1E19 cm -3 The Mg doping concentration of the third P-type semiconductor layer is greater than 5E20 cm⁻¹. -3 .
22. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The number of periods in the superlattice structure of the first P-type semiconductor layer is 10 to 20.
23. The method for preparing the LED epitaxial structure as described in claim 22, characterized in that, The thickness of the first P-type semiconductor layer is 15nm~70nm, and the thickness of the AlN layer in each cycle is 0.7nm~2nm, the thickness of the first Mg layer is 0.3nm~0.5nm, and the thickness of the first MgN layer is 0.5nm~1nm.
24. The method for preparing an LED epitaxial structure as described in claim 22, characterized in that, The thickness of a single cycle of the AlN layer gradually decreases along the growth direction of the first P-type semiconductor layer.
25. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The material of the second P-type semiconductor layer includes at least one of GaN, AlGaN and AlInGaN, and the thickness of the second P-type semiconductor layer is 20nm~200nm.
26. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The third P-type semiconductor layer is In x Ga (1-x) The superlattice structure is formed by alternating growth of N layer, second Mg layer and second MgN layer, with x ranging from 0.005 to 0.02 and the number of periods of the superlattice structure ranging from 5 to 10.
27. The method for preparing an LED epitaxial structure as described in claim 26, characterized in that, The In x Ga (1-x) The In composition of a single cycle in the N layer gradually increases along the growth direction of the third P-type semiconductor layer.
28. The method for preparing an LED epitaxial structure as described in claim 26, characterized in that, The thickness of the third P-type semiconductor layer is 7.5 nm to 35 nm, and the In in each cycle x Ga (1-x) The thickness of the N layer is 0.7 nm to 2 nm, the thickness of the second Mg layer is 0.3 nm to 0.5 nm, and the thickness of the second MgN layer is 0.5 nm to 1 nm.
29. The method for preparing an LED epitaxial structure as described in claim 28, characterized in that, The In x Ga (1-x) The thickness of a single cycle of the N-layer gradually increases along the growth direction of the third P-type semiconductor layer.
30. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The N-type semiconductor layer includes a first N-type semiconductor layer, a second N-type semiconductor layer, and a third N-type semiconductor layer stacked sequentially. The first N-type semiconductor layer, the second N-type semiconductor layer, and the third N-type semiconductor layer are doped with Si, and the Si doping concentration of the second N-type semiconductor layer is less than the Si doping concentration of the first N-type semiconductor layer and less than the Si doping concentration of the third N-type semiconductor layer.
31. The method for preparing an LED epitaxial structure as described in claim 30, characterized in that, The Si doping concentration of the first N-type semiconductor layer is 1E18cm⁻¹ -3 ~1E19cm -3 The Si doping concentration of the second N-type semiconductor layer is 1E17 cm⁻¹. -3 ~1E18cm -3 The Si doping concentration of the third N-type semiconductor layer is 1E19 cm⁻¹. -3 ~1E20 cm -3 .
32. The method for preparing an LED epitaxial structure as described in claim 30, characterized in that, The first N-type semiconductor layer is a first Si layer, a first SiN layer, and an Al layer. a Ga (1-a) The superlattice structure is formed by the sequential growth of N layers, where a ranges from 0.01 to 0.1, and the number of periods in the superlattice structure is from 5 to 10.
33. The method for preparing the LED epitaxial structure as described in claim 32, characterized in that, The thickness of the first N-type semiconductor layer is 100nm~500nm, and the thickness of the first Si layer in each period is 0.2nm~0.5nm, the thickness of the first SiN layer is 0.3nm~1nm, and the Al... a Ga (1-a) The thickness of the N layer ranges from 19.5 nm to 48.5 nm.
34. The method for preparing an LED epitaxial structure as described in claim 30, characterized in that, The material of the second N-type semiconductor layer includes at least one of GaN, AlGaN and AlInGaN, and the thickness of the second N-type semiconductor layer is 100nm~500nm.
35. The method for preparing an LED epitaxial structure as described in claim 30, characterized in that, The third N-type semiconductor layer is a superlattice structure formed by alternating growth of the second Si layer, the second SiN layer and the GaN layer, and the number of periods of the superlattice structure is 10 to 20.
36. The method for preparing an LED epitaxial structure as described in claim 35, characterized in that, The thickness of the third N-type semiconductor layer is 500nm~2000nm, and the thickness of the second Si layer in each cycle is 0.2nm~0.5nm, the thickness of the second SiN layer is 0.3nm~1nm, and the thickness of the GaN layer is 49.5nm~98.5nm.
37. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The LED epitaxial structure further includes an electron blocking layer, which is located between the active layer and the first P-type semiconductor layer.
38. The method for preparing an LED epitaxial structure as described in claim 20, characterized in that, The LED epitaxial structure further includes a stress buffer layer, which is located between the N-type semiconductor layer and the active layer.