LED epitaxial structure and preparation method thereof

Abstract

The present invention provides an LED epitaxial structure and a preparation method thereof, wherein the LED epitaxial structure comprises, from bottom to top, a bottom buffer layer located on a substrate, a corrosion stop layer, a first-type semiconductor layer, an active layer, and a second-type semiconductor layer, wherein the second-type semiconductor layer comprises, from bottom to top, a second-type barrier layer, a second-type restriction layer, a strain buffer layer, a second-type current spreading layer, and a second-type ohmic contact layer, and the strain buffer layer is (Al x Ga 1‑x ) 0.5 In 0.5 P, GaP and (Al y Ga 1‑y ) 0.5 In 0.5 The present invention can improve the crystal quality of the epitaxial structure by growing a strain buffer layer, thereby reducing the operating voltage of the LED device and improving its luminous efficiency.

Description

Technical Field

[0001] The technical solution of the present invention belongs to the technical field of LED epitaxial growth, and specifically relates to an LED epitaxial structure and a preparation method thereof. Background Art

[0002] Light Emitting Diode (LED) is a semiconductor solid-state light-emitting device that uses semiconductor PN junction as the light-emitting material and can directly convert electrical energy into light energy. In recent years, LED has been widely used due to its advantages such as low power consumption, long life, small size, energy saving and environmental protection. In particular, with the maturity of metal organic chemical vapor deposition (MOCVD) epitaxial growth technology, red light LED represented by gallium arsenide (GaAs) has developed rapidly and started large-scale commercialization.

[0003] The crystal quality of LED epitaxial structure plays a vital role in the performance of LED devices. LED epitaxial structure with high crystal quality can be used to make LED devices to obtain lower operating voltage and luminous efficiency. At present, AlGaInP-based red LED devices on the market generally grow a layer of GaP in their epitaxial structure as a current spreading layer to improve the current spreading effect when the LED device is working. For LED devices, especially large-sized LED devices, the current spreading effect greatly affects the performance of LED devices. The poor crystal quality of the current spreading layer will cause uneven current spreading, resulting in excessive local current density and excessive junction temperature, which will greatly increase the operating voltage of the LED device and greatly reduce the luminous efficiency and life. Therefore, the crystal quality of the current spreading layer has a great impact on the performance of the LED. However, there is a large lattice mismatch between the current spreading layer and the substrate, and the lattice mismatch will introduce mismatch stress during the epitaxial growth process. The generation of mismatch stress leads to an increase in defects in the epitaxial structure, which seriously weakens the various performances of the LED device. And when there is a large lattice mismatch between the epitaxial structure and the substrate, the surface free energy of the substrate is less than the sum of the surface and interface energy of the epitaxial structure, and the bond energy between the substrate and the epitaxial structure is not very high, the substrate surface cannot form a wetting layer, resulting in the appearance of a three-dimensional island, which then continues to grow into a columnar island, causing the surface of the epitaxial structure to be rough. Moreover, if the dislocation defects generated by the epitaxial structure under a large lattice mismatch are not effectively suppressed, the dislocation defects will move upward with the epitaxial growth until the surface of the epitaxial structure, reducing the crystal quality and seriously affecting the performance of the LED device.

[0004] Therefore, it is necessary to provide an LED epitaxial structure and its preparation method to reduce lattice mismatch stress and defects, so as to improve the crystal quality of the epitaxial structure and the radiation recombination probability of carriers, thereby reducing the operating voltage of the LED device and improving its luminous efficiency. Summary of the invention

[0005] The present invention provides an LED epitaxial structure and a preparation method thereof, so as to improve the crystal quality of the epitaxial structure, thereby improving the luminous efficiency of the LED device and reducing the operating voltage of the LED device.

[0006] In order to achieve the above-mentioned object and other related objects, the present invention provides an LED epitaxial structure, which comprises, from bottom to top, a bottom buffer layer, an etching stop 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 comprises, from bottom to top, a second-type barrier layer, a second-type confinement layer, a strain buffer layer, a second-type current spreading layer, and a second-type ohmic contact layer, and the strain buffer layer is (Al x Ga 1-x ) 0.5 In 0.5 P, GaP and (Al y Ga 1-y ) 0.5 In 0.5 P, where 0.10≤x≤0.50 and 0.05≤y≤0.10.

[0007] Optionally, in the LED epitaxial structure, the strain buffer layer is a single-period structure or a multi-period structure.

[0008] Optionally, in the LED epitaxial structure, each periodic structure of the strain buffer layer includes a first structure layer, a second structure layer and a third structure layer stacked in sequence, wherein the material of the first structure layer includes (Al x Ga 1-x ) 0.5 In 0.5 P; the material of the second structural layer includes GaP; the material of the third structural layer includes (Al y Ga 1-y ) 0.5 In 0.5 P.

[0009] Optionally, in the LED epitaxial structure, the thickness of the strain buffer layer is 50nm~120nm, the total thickness of the first structural layer in all periods is 10nm~30nm, the total thickness of the second structural layer in all periods is 30nm~60nm, and the total thickness of the third structural layer in all periods is 10nm~30nm.

[0010] Optionally, in the LED epitaxial structure, the first structure layer, the second structure layer and the third structure layer are all doped with Mg, and the doping concentration of Mg is 1E18cm -3~5E18 cm -3 .

[0011] Optionally, in the LED epitaxial structure, the Al components in the first structure layer and the third structure layer are gradually changed.

[0012] Optionally, in the LED epitaxial structure, the Al component in the first structural layer gradually decreases along the growth direction of the first structural layer.

[0013] Optionally, in the LED epitaxial structure, the Al component in the third structural layer gradually decreases along the growth direction of the third structural layer.

[0014] Optionally, in the LED epitaxial structure, the first-type semiconductor layer includes a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer and a first-type barrier layer, and the first-type ohmic contact layer is located between the corrosion stop layer and the first-type window layer, and the first-type barrier layer is located between the first confinement layer and the active layer.

[0015] Optionally, in the LED epitaxial structure, the first-type semiconductor layer is an n-type semiconductor layer, and the second-type semiconductor layer is a p-type semiconductor layer.

[0016] Optionally, in the LED epitaxial structure, the substrate includes a GaAs substrate or a Si substrate.

[0017] 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:

[0018] providing a substrate;

[0019] Growing a bottom buffer layer, an etching stop layer, a first type semiconductor layer and an active layer in sequence on the substrate;

[0020] A second-type semiconductor layer is grown on the active layer, wherein the second-type semiconductor layer includes, from bottom to top, a second-type barrier layer, a second-type confinement layer, a strain buffer layer, a second-type current spreading layer, and a second-type ohmic contact layer, and the strain buffer layer is (Al x Ga 1-x ) 0.5 In 0.5 P, GaP and (Al y Ga 1-y ) 0.5 In 0.5 P, where 0.10≤x≤0.50 and 0.05≤y≤0.10.

[0021] Optionally, in the method for preparing the LED epitaxial structure, the strain buffer layer is a single-period structure or a multi-period structure.

[0022] Optionally, in the method for preparing the LED epitaxial structure, each periodic structure of the strain buffer layer includes a first structure layer, a second structure layer and a third structure layer stacked in sequence, wherein the material of the first structure layer includes (Al x Ga 1-x ) 0.5 In 0.5 P; the material of the second structural layer includes GaP; the material of the third structural layer includes (Al y Ga 1-y ) 0.5 In 0.5 P.

[0023] Optionally, in the preparation method of the LED epitaxial structure, the thickness of the strain buffer layer is 50nm~120nm, the total thickness of the first structural layer in all periods is 10nm~30nm, the total thickness of the second structural layer in all periods is 30nm~60nm, and the total thickness of the third structural layer in all periods is 10nm~30nm.

[0024] Optionally, in the method for preparing the LED epitaxial structure, the first structural layer, the second structural layer and the third structural layer are all doped with Mg, and the doping concentration of Mg is 1E18cm -3 ~5E18 cm -3 .

[0025] Optionally, in the method for preparing the LED epitaxial structure, the Al components in the first structural layer and the third structural layer are gradually changed.

[0026] Optionally, in the method for preparing the LED epitaxial structure, the Al component in the first structural layer gradually decreases along the growth direction of the first structural layer.

[0027] Optionally, in the method for preparing the LED epitaxial structure, the Al component in the third structural layer gradually decreases along the growth direction of the third structural layer.

[0028] Optionally, in the method for preparing the LED epitaxial structure, the first-type semiconductor layer includes a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer and a first-type barrier layer, and the first-type ohmic contact layer is located between the corrosion stop layer and the first-type window layer, and the first-type barrier layer is located between the first confinement layer and the active layer.

[0029] Optionally, in the method for preparing the LED epitaxial structure, the first-type semiconductor layer is an n-type semiconductor layer, and the second-type semiconductor layer is a p-type semiconductor layer.

[0030] Optionally, in the method for preparing the LED epitaxial structure, the substrate includes a GaAs substrate or a Si substrate.

[0031] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0032] The present invention adds a strain buffer layer between the second type restriction layer and the second type current spreading layer, so that the stress caused by the lattice mismatch between the second type restriction layer and the second type current spreading layer can be concentrated in the strain buffer layer, thereby making the second type restriction layer and the second type current spreading layer have a better lattice match, and improving the crystal quality of the second type current spreading layer. At the same time, since the layers of the LED epitaxial structure are alternately under compressive stress and tensile stress, the dislocations are bent and extended to each layer, and the strain buffer layer can serve as a barrier layer for the dislocation extension, so that the dislocations of each layer are reduced, the generation of cracks can be reduced, the crystal quality is improved, and the luminous efficiency of the LED device is improved and the operating voltage of the LED device is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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.

[0034] Figure 1 is a schematic structural diagram of an LED epitaxial structure according to an embodiment of the present invention;

[0035] Figure 2 is a schematic structural diagram of a strain buffer layer according to an embodiment of the present invention;

[0036] Figure 3 is a flow chart of a method for preparing an LED epitaxial structure according to an embodiment of the present invention;

[0037] in Figure 1-2 middle:

[0038] 100-substrate, 101-bottom buffer layer, 102-corrosion stop layer, 103-first type ohmic contact layer, 104-first type window layer, 105-first type confinement layer, 106-first type barrier layer, 107-active layer, 108-second type barrier layer, 109-second type confinement layer, 110-strain buffer layer, 1101-first structure layer, 1102-second structure layer, 1103-third structure layer, 111-second type current spreading layer, 112-second type ohmic contact layer. DETAILED DESCRIPTION

[0039] 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.

[0040] Before describing the embodiments of the present invention, the following contents are described in advance. First, in this specification, when simply marked as "AlInP", it means an arbitrary compound in which 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 simply marked as "GaInP", it means an arbitrary compound in which 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.

[0041] Figure 1 FIG. 1 is a schematic diagram of the structure of the LED epitaxial structure of this embodiment. Figure 1 The LED epitaxial structure includes, from bottom to top, a bottom buffer layer 101, an etching stop layer 102, a first-type semiconductor layer, an active layer 107, and a second-type semiconductor layer on a substrate 100. The second-type semiconductor layer includes, from bottom to top, a second-type barrier layer 108, a second-type confinement layer 109, a strain buffer layer 110, a second-type current spreading layer 111, and a second-type ohmic contact layer 112. The strain buffer layer 110 is (Al x Ga 1-x ) 0.5 In 0.5 P, GaP and (Al y Ga 1-y ) 0.5 In 0.5 P, where 0.10≤x≤0.50 and 0.05≤y≤0.10.

[0042] The first-type semiconductor layer includes, from bottom to top, a first-type ohmic contact layer 103, a first-type window layer 104, and a first-type confinement layer 105, and the first-type window layer 104 is a structure layer with a gradient Al composition. The first-type semiconductor layer also includes a first-type barrier layer 106, and the first-type barrier layer 106 is located between the first-type confinement layer 105 and the active layer 107.

[0043] The polarity of the first-type semiconductor layer is opposite to that of the second-type semiconductor layer. For example, if the first-type semiconductor layer is an n-type semiconductor layer, the corresponding second-type semiconductor layer is a p-type semiconductor layer. Accordingly, the n-type semiconductor layer includes an n-type ohmic contact layer, an n-type window layer, an n-type confinement layer, and an n-type barrier layer stacked in sequence. The p-type semiconductor layer includes a p-type barrier layer, a p-type confinement layer, a strain buffer layer, a p-type current spreading layer, and a p-type ohmic contact layer stacked in sequence. The first-type barrier layer 106 and the second-type barrier layer 108 are undoped layers.

[0044] See also Figure 3 The method for preparing the LED epitaxial structure specifically comprises the following steps:

[0045] Step S1: providing a substrate 100;

[0046] Step S2: sequentially growing a bottom buffer layer 101, an etching stop layer 102, a first type semiconductor layer and an active layer 107 on the substrate 100;

[0047] Step S3: growing a second-type semiconductor layer on the active layer 107, wherein the second-type semiconductor layer includes, from bottom to top, a second-type barrier layer 108, a second-type confinement layer 109, a strain buffer layer 110, a second-type current spreading layer 111, and a second-type ohmic contact layer 112, and the strain buffer layer 110 is (Al x Ga 1-x ) 0.5 In 0.5 P, GaP and (Al y Ga 1-y ) 0.5 In 0.5 P, where 0.10≤x≤0.50 and 0.05≤y≤0.10.

[0048] The preparation process of the LED epitaxial structure is any one of metal organic chemical vapor deposition (MOCVD) process, molecular beam epitaxy (MBE) process or ultra-high vacuum chemical vapor deposition (UHVCVD), preferably MOCVD process. The following specific embodiments are described by taking MOCVD process as an example.

[0049] In step S1 , the substrate 100 is preferably a GaAs (gallium arsenide) substrate, and may also be a Si (silicon) substrate, but is not limited thereto.

[0050] In step S2, a bottom buffer layer 101 is grown on the substrate 100. The bottom buffer layer 101 can eliminate the influence of the surface defects of the substrate 100 on the LED epitaxial structure to the greatest extent, reduce the defects and dislocations of the LED epitaxial structure, and provide a smooth interface for the next growth. The material of the bottom buffer layer 101 is preferably GaAs, but not limited to this. The first-type dopant, such as an n-type dopant, doped in the bottom buffer layer 101 can be at least one of silicon (Si) and tellurium (Te), but not limited to this. Furthermore, the first-type dopant is preferably Si.

[0051] The bottom buffer layer 101 is preferably grown in a reaction chamber of a MOCVD growth furnace to grow a bottom buffer layer 101 with a thickness of 100 nm to 400 nm. Preferably, the bottom buffer layer 101 is grown with a thickness of 200 nm.

[0052] After the bottom buffer layer 101 is grown, an etch stop layer 102 is grown on the bottom buffer layer 101. The material of the etch stop layer 102 is preferably GaInP, but not limited thereto. The etch stop layer 102 is doped with a first-type dopant, such as an n-type dopant, which may be at least one of silicon (Si) and tellurium (Te), but not limited thereto. Further, the first-type dopant is preferably Si.

[0053] The corrosion stop layer 102 is preferably grown in a reaction chamber of a MOCVD growth furnace to grow a corrosion stop layer 102 with a thickness of 150 nm to 300 nm. Preferably, the corrosion stop layer 102 is grown with a thickness of 200 nm.

[0054] After the etching stop layer 102 is grown, a first-type semiconductor layer is grown on the etching stop layer 102. The first-type semiconductor layer includes a first-type window layer 104 and a first-type confinement layer 105 from bottom to top, and the first-type window layer 104 is a structure layer with a gradient Al composition.

[0055] The first-type semiconductor layer may further include a first-type ohmic contact layer 103 , and the first-type ohmic contact layer 103 is located between the corrosion stop layer 102 and the first-type window layer 104 .

[0056] Therefore, after the etching stop layer 102 is grown, the first-type ohmic contact layer 103 is grown on the etching stop layer 102. The material of the first-type ohmic contact layer 103 can be AlGaInP or GaAs, preferably GaAs, but not limited thereto. The first-type ohmic contact layer 103 is doped with a first-type dopant, such as an n-type dopant, which can be one of silicon (Si) and tellurium (Te), but not limited thereto. Further, the first-type dopant is preferably Si.

[0057] The first type ohmic contact layer 103 is preferably grown in a reaction chamber of a MOCVD growth furnace to a thickness of 40 nm to 150 nm. Preferably, the first type ohmic contact layer 103 is grown to a thickness of 90 nm.

[0058] After the first-type ohmic contact layer 103 is grown, the first-type window layer 104 is grown on the first-type ohmic contact layer 103. The main functions of the first-type window layer 104 are first-type current expansion, light extraction and surface roughening. Because this layer is mainly for current expansion and surface roughening, and the Al component gradient makes it easier to roughen, it can reduce the multiple reflections of light inside the LED epitaxial structure and refract the light from the inside. Therefore, the Al component gradient of the first-type window layer 104 can improve the light extraction efficiency. Moreover, the Al component gradient of the first-type window layer 104 improves the current expansion, making it easier for the current to expand out and not gather under the electrode. At the same time, the Al component gradient can also reduce its potential barrier. Therefore, the first-type window layer 104 can reduce the operating voltage of the LED device.

[0059] The material of the first-type window layer 104 is preferably AlGaInP, doped with a first-type dopant, such as an n-type dopant, which can be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Furthermore, the first-type dopant is preferably Si. The Al component in the AlGaInP of the first window layer 104 grows in a gradual manner, and the gradual manner is: along the growth direction of the first window layer 104, the Al component gradually changes from 0.15 to 0.45 and then to 0.15. That is, along the growth direction of the first window layer 104, the first window layer 104 is composed of (Al 0.15 Ga 0.85 ) 0.5 In 0.5 P gradually changes to (Al 0.45 Ga 0.55 ) 0.5 In 0.5 P then gradually changes to (Al 0.15 Ga 0.85 ) 0.5 In 0.5P. Preferably, the (Al 0.15 Ga 0.85 ) 0.5 In 0.5 P gradually changes to (Al 0.45 Ga 0.55 ) 0.5 In 0.5 P and (Al 0.45 Ga 0.55 ) 0.5 In 0.5 P gradually changes to (Al 0.15 Ga 0.85 ) 0.5 In 0.5 The thickness of P is consistent, which is half the thickness of the first window layer 104, which is beneficial to reduce voltage and improve brightness. The growth of the first window layer 104 is preferably to grow a first window layer 104 with a thickness of 1 μm to 5 μm in the reaction chamber of an MOCVD growth furnace. Preferably, the first window layer 104 is grown with a thickness of 2 μm.

[0060] After the first-type window layer 104 is grown, the first-type confinement layer 105 is grown on the first-type window layer 104. The material of the first-type confinement layer 105 is preferably AlInP, but not limited thereto. The first-type confinement layer 105 is doped with a first-type dopant, such as an n-type dopant, which may be at least one of silicon (Si) and tellurium (Te), but not limited thereto. Further, the first-type dopant is preferably Si.

[0061] The first type confinement layer 105 is preferably grown in a reaction chamber of a MOCVD growth furnace to grow a first type confinement layer 105 with a thickness of 100 nm to 500 nm. Preferably, the first type confinement layer 105 is grown with a thickness of 300 nm.

[0062] After the first-type confinement layer 105 is grown, the first-type barrier layer 106 is grown on the first-type confinement layer 105. The material of the first-type barrier layer 106 is preferably AlGaInP, but not limited thereto. The first-type barrier layer 106 is undoped.

[0063] After growing the first-type barrier layer 106, the active layer 107 is grown on the first-type barrier layer 106. The active layer 107 is preferably a multi-quantum well structure, that is, the active layer 107 is preferably a periodic structure composed of quantum wells and quantum barriers, and the number of periods of the active layer 107 is preferably 6 to 18. The active layer 107 is preferably made of AlGaInP and GaInP, wherein the material of the quantum well is preferably GaInP, and the material of the quantum barrier is preferably AlGaInP. The thickness of the active layer 107 is 90nm to 500nm, preferably 150nm.

[0064] The growth of the active layer 107 is preferably performed by growing 6 to 18 periods of the active layer 107 in the reaction chamber of the MOCVD growth furnace. For example, 6 periods of the active layer 107 are grown.

[0065] In step S3, after growing the active layer 107, a second-type semiconductor layer is grown on the active layer 107. The second-type semiconductor layer includes, from bottom to top, a second-type barrier layer 108, a second-type confinement layer 109, a strain buffer layer 110, a second-type window layer 111, and a second-type ohmic contact layer 112.

[0066] Therefore, after the active layer 107 is grown, a second type barrier layer 108 is grown on the active layer 107 , and the material of the second type barrier layer 108 is preferably AlGaInP, but not limited thereto. The second type barrier layer 108 is undoped.

[0067] The second type barrier layer 108 is preferably grown in a reaction chamber of a MOCVD growth furnace to grow a second type barrier layer 108 with a thickness of 100 nm to 300 nm. Preferably, the second type barrier layer 108 is grown with a thickness of 200 nm.

[0068] After the second type barrier layer 108 is grown, a second type confinement layer 109 is grown on the second type barrier layer 108. The second type confinement layer 109 is used to provide holes. Moreover, the first type confinement layer 105 and the second type confinement layer 109 as confinement layers have two main functions: on the one hand, they limit minority carriers from overflowing the active layer 107, thereby improving the composite luminous efficiency; on the other hand, they serve as an important window, allowing the photons emitted by the active layer 107 to easily pass through the confinement layer, thereby improving the luminous efficiency of the LED device.

[0069] The material of the second type confinement layer 109 is preferably AlInP, but not limited thereto. The second type confinement layer 109 is doped with a second type dopant, such as a p-type dopant, which may be at least one of magnesium (Mg) and zinc (Zn), but not limited thereto. Further, the second type dopant is preferably Mg.

[0070] The second type confinement layer 109 is preferably grown in a reaction chamber of a MOCVD growth furnace to grow a second type confinement layer 109 with a thickness of 150 nm to 500 nm. Preferably, the second type confinement layer 109 is grown with a thickness of 300 nm.

[0071] After the second type confinement layer 109 is grown, a strain buffer layer 110 is grown on the second type confinement layer 109. The strain buffer layer 110 includes a single-period or multi-period structure consisting of a first structure layer 1101, a second structure layer 1102, and a third structure layer 1103, that is, the strain buffer layer 110 is a single-period structure or a multi-period structure, and each periodic structure includes a first structure layer 1101, a second structure layer 1102, and a third structure layer 1103 stacked in sequence. If the strain buffer layer 110 is a multi-period structure, its period is determined by the period number k, which ranges from 2 to 10.

[0072] See also Figure 1 The thickness of the strain buffer layer 110 is preferably 50nm to 120nm. The material of the first structural layer 1101 is preferably (Al x Ga 1-x ) 0.5 In 0.5 P, x is in the range of 0.10≤x≤0.50, and the total thickness of the first structure layer 1101 in all periods is 10nm-30nm, for example, the total thickness of the first structure layer 1101 in all periods is 25nm. The material of the second structure layer 1102 is preferably GaP, and the total thickness of the second structure layer 1102 in all periods is 30nm-60nm, for example, the total thickness of the second structure layer 1102 in all periods is 50nm. The material of the third structure layer 1103 is (Al y Ga 1-y ) 0.5 In 0.5 The range of P, y is 0.05≤y≤0.10, and the total thickness of the third structure layer 1103 in all periods is 10 nm to 30 nm. For example, the total thickness of the third structure layer 1103 in all periods is 20 nm.

[0073] The strain buffer layer 110 is doped with a second-type dopant, such as a p-type dopant, which may be at least one of magnesium (Mg) and zinc (Zn), but is not limited thereto. That is, the first structure layer 1101, the second structure layer 1102, and the third structure layer 1103 are all doped with a second-type dopant, and the concentrations of the second-type dopant doped in the first structure layer 1101, the second structure layer 1102, and the third structure layer 1103 are preferably the same. Further, the second-type dopant is preferably Mg, for example, the first structure layer 1101, the second structure layer 1102, and the third structure layer 1103 are all doped with Mg, and the doping concentration of Mg is 1E18cm -3 ~5E18 cm -3 .

[0074] The strain buffer layer 110 is grown by first growing the first structure layer 1101, then growing the second structure layer 1102, and then growing the third structure layer 1103. If the strain buffer layer 110 is a multi-periodic structure, it is grown cyclically according to the above growth method, and the cycle period is determined by the cycle number k.

[0075] The first structure layer 1101 of the strain buffer layer 110 is grown on the second confinement layer 109. Since the lattice constant of the AlGaInP material is close to that of the AlInP material and is within the lattice matching range, a high-quality first structure layer 1101 can be grown on the second confinement layer 109, and the stress borne by both is very small.

[0076] The strain buffer layer 110 includes a structure layer with a gradient Al component. Specifically, the Al components in the first structure layer 1101 and the third structure layer 1103 are gradient. The gradient range of the Al component in the first structure layer 1101 is between 0.10 and 0.50, and the gradient range of the Al component in the third structure layer 1103 is between 0.05 and 0.1. The Al components in the first structure layer 1101 and the third structure layer 1103 are gradient and different. The function is to use the different Al components to cause different energy band barriers to form a slowly changing barrier, thereby reducing the operating voltage of the LED device.

[0077] The Al component in the first structural layer 1101 gradually decreases along the growth direction of the first structural layer 1101. For example, the Al component in the first structural layer 1101 gradually changes from (Al) to (Al) along the growth direction of the first structural layer 1101. 0.5 Ga 0.5 ) 0.5 In 0.5 P gradually changes to (Al 0.10 Ga 0.9 ) 0.5 In 0.5 In other embodiments, the gradient range of the Al component can be changed, as long as the Al component gradually decreases along the growth direction of the first structural layer 1101, and the gradient range of the Al component is between 0.10 and 0.50. For example, along the growth direction of the first structural layer 1101, (Al 0.4 Ga 0.6 ) 0.5 In 0.5 P gradually changes to (Al 0.10 Ga 0.9 ) 0.5 In 0.5 P.

[0078] The Al component in the third structural layer 1103 gradually decreases along the growth direction of the third structural layer 1103. For example, the Al component in the third structural layer 1103 gradually changes from (Al 0.1 Ga 0.9 ) 0.5 In 0.5 P gradually changes to (Al 0.05 Ga 0.95 ) 0.5 In 0.5 In other embodiments, the gradient range of the Al component can be changed, as long as the Al component gradually decreases along the growth direction of the third structural layer 1103, and the gradient range of the Al component is between 0.05 and 0.1. For example, along the growth direction of the third structural layer 1103, (Al 0.08 Ga 0.92 ) 0.5 In 0.5 P gradually changes to (Al 0.05 Ga 0.95 ) 0.5 In 0.5 P.

[0079] The material of the first structure layer 1101 is AlGaInP with a gradient Al component, and the lattice constant of the first structure layer 1101 is greatly different from that of the material GaP of the second structure layer 1102, which will generate a large mismatch stress. At the same time, the material of the third structure layer 1103 is also AlGaInP with a gradient Al component, and this layer will also generate mismatch stress to the material GaP of the second structure layer 1102. The stress generated by the lattice constant of the first structure layer 1101 and the second structure layer 1102 and the stress generated by the lattice constant of the second structure layer 1102 and the third structure layer 1103 will be absorbed by the second structure layer 1102 to form a stress absorption layer. That is, both sides of the second structure layer 1102 are made of the same material, for example, the material of both sides of the second structure layer 1102 is AlGaInP, and the GaP of the second structure layer 1102 will cause lattice deformation and generate stress due to different lattice constants. The generated stress will be applied to the second structure layer 1102 and absorbed by the second structure layer 1102. Similarly, the stress generated between the second structure layer 1102 and the third structure layer 1103 and between the third structure layer 1103 and the second type current spreading layer 111 will also be absorbed by the third structure layer 1103 to form a stress absorption layer. That is, both sides of the third structure layer 1103 are made of the same material. For example, both sides of the third structure layer 1103 are made of GaP, which will cause lattice deformation and generate stress due to different lattice constants of AlGaInP of the third structure layer 1103. The generated stress will be applied to the third structure layer 1103 and absorbed by the third structure layer 1103. The two layers of stress absorption layers formed play a role of stress buffering, thereby improving the crystal quality of the second type current spreading layer 111.

[0080] Since the lattice constant of GaP is 5.45, which is mismatched with the lattice constant of GaAs 5.65 and the lattice constant of AlInP 5.67, the mismatch degree is about 3.58%, which is a large mismatch. Therefore, if there is no stress buffer layer 110, there is a large lattice mismatch between the AlInP of the second type confinement layer 109 and the GaP of the second type current spreading layer 111, which will produce a large mismatch stress, and the crystal quality of the GaP of the second type current spreading layer 111 will be poor. At the same time, the stress generated by the mismatch will pull and tear the epitaxial structure, and will also increase the defects of other epitaxial structures, and the crystal quality will deteriorate, and finally the performance of the LED device will be reduced, for example, the high temperature aging stability of the LED device will deteriorate. The main reason for the deterioration of the high temperature aging stability of the LED device is: poor crystal quality, increased epitaxial defects, and increased non-radiative recombination centers, which will increase the probability of forming non-radiative recombination. Non-radiative recombination does not generate photons, but generates heat energy. The increase of heat energy in the LED device will lead to an increase in junction temperature, so that the LED device works above the rated temperature, accelerating its aging and light decay, so the high temperature aging stability of the LED device will be relatively poor.

[0081] The Al component in the AlGaInP of the first structure layer 1101 and the third structure layer 1103 grows gradually, and the lattice constants thereof match those of AlInP. For example, (Al 0.5 Ga 0.5 ) 0.5 In 0.5 P、(Al 0.1 Ga 0.9 ) 0.5 In 0.5 P and (Al 0.05 Ga 0.95 ) 0.5 In 0.5 The lattice constant of P matches that of AlInP of the second-type confinement layer 109, so the stress buffer layer 110 can be well grown on the AlInP of the second-type confinement layer 109. After inserting a structure composed of AlGaInP, GaP and AlGaInP into the original structure as a stress buffer layer for growing GaP of the second-type current spreading layer 111, the stress caused by the mismatch is completely concentrated in the strain buffer layer 110, compressing the lattice, so that the AlInP of the second-type confinement layer 109 and the GaP of the second-type current spreading layer 111 have a good lattice match, and the second-type current spreading layer 111 with high crystal quality can be grown.

[0082] Moreover, GaP of the second structure layer 1102 is inserted between the AlGaInP of the first structure layer 1101 and the AlGaInP of the third structure layer 1103, so that two stress absorption layers are formed between the GaP of the second current spreading layer 111 and the AlInP of the second confinement layer 109, thereby reducing the pulling of the epitaxial structure caused by the stress between the GaP of the second current spreading layer 111 and the AlInP of the second confinement layer 109, reducing the number of defects in the epitaxial structure, and improving the crystal quality of the epitaxial structure, thereby improving the luminous efficiency of the LED device, reducing the operating voltage of the LED device, and improving the high-temperature aging stability of the LED device. At the same time, because each layer of the epitaxial structure is alternately under compressive stress and tensile stress, the dislocations are bent and spread to each layer, and the GaP inserted between the two layers of AlGaInP in the stress buffer layer 110 can block the dislocations generated by stress pulling from spreading to other epitaxial structures, reduce the generation of epitaxial defects, and improve the crystal quality of the epitaxial structure. That is, the stress buffer layer 110 can serve as a dislocation expansion barrier layer to reduce dislocations in each layer and prevent cracks caused by lattice mismatch.

[0083] In addition, due to its three-layer structure, the strain buffer layer 110 has a certain elastic deformation inside, which affects its energy band structure, especially the valence band. Due to the introduction of strain potential, the heavy hole and light hole bands are separated, reducing the effective mass of the holes, reducing the state density, and reducing the threshold current of the LED device.

[0084] After growing the strain buffer layer 110, a second type current spreading layer 111 is grown on the strain buffer layer 110. The second type current spreading layer 111 is used for current spreading to prevent uneven current distribution in the LED device. The material of the second type current spreading layer 111 is preferably GaP, but not limited thereto. The doping source of the second type current spreading layer 111 is preferably Mg, but not limited thereto.

[0085] The second type current spreading layer 111 is preferably grown to a thickness of 300nm to 900nm in a reaction chamber of a MOCVD growth furnace. Preferably, the second type current spreading layer 111 is grown to a thickness of 600nm.

[0086] After the second-type current spreading layer 111 is grown, the second-type ohmic contact layer 112 is grown on the second-type current spreading layer 111. The second-type ohmic contact layer 112 is used to form an ohmic contact with a metal electrode. The material of the second-type ohmic contact layer 112 is preferably GaP, but not limited thereto. The second-type ohmic contact layer 112 may be doped with carbon (C).

[0087] The second type ohmic contact layer 112 is preferably grown in a reaction chamber of a MOCVD growth furnace to grow the second type ohmic contact layer 112 with a thickness of 100 nm to 250 nm. Preferably, the second type ohmic contact layer 112 is grown with a thickness of 200 nm.

[0088] The present invention adds a strain buffer layer between the second type restriction layer and the second type current spreading layer, so that the stress caused by the lattice mismatch between the second type restriction layer and the second type current spreading layer can be completely concentrated in the strain buffer layer, thereby making the second type restriction layer and the second type current spreading layer have a good lattice match, and improving the crystal quality of the second type current spreading layer. At the same time, since the layers of the LED epitaxial structure are alternately under compressive stress and tensile stress, the dislocations are bent and extended to each layer, and the strain buffer layer can serve as a barrier layer for the dislocation extension, so that the dislocations of each layer are reduced, the generation of cracks can be reduced, the crystal quality is improved, and the luminous efficiency of the LED device is improved and the operating voltage of the LED device is reduced.

[0089] 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.

[0090] 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, and are not used 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. Therefore, 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", not 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 LED epitaxial structure includes, from bottom to top, a bottom buffer layer, a corrosion stop 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 barrier layer, a second-type confinement layer, a strain buffer layer, a second-type current spreading layer, and a second-type ohmic contact layer, and the strain buffer layer is a single-period structure or a multi-period structure, and each period of the strain buffer layer includes a first structure layer, a second structure layer, and a third structure layer stacked in sequence, wherein the material of the first structure layer includes (Al x Ga 1-x ) 0.5 In 0.5 P; the material of the second structural layer includes GaP; the material of the third structural layer includes (Al y Ga 1-y ) 0.5 In 0.5 P, where 0.10≤x≤0.50, 0.05≤y≤0.

10.

2. The LED epitaxial structure according to claim 1, characterized in that: The thickness of the strain buffer layer is 50nm-120nm, wherein the total thickness of the first structural layer in all periods is 10nm-30nm, the total thickness of the second structural layer in all periods is 30nm-60nm, and the total thickness of the third structural layer in all periods is 10nm-30nm.

3. The LED epitaxial structure according to claim 1, characterized in that: The first structure layer, the second structure layer and the third structure layer are all doped with Mg, and the doping concentration of Mg is 1E18cm -3 ~5E18 cm -3 .

4. The LED epitaxial structure according to claim 1, characterized in that: The Al compositions in the first structural layer and the third structural layer are graded.

5. The LED epitaxial structure according to claim 4, characterized in that: The Al component in the first structural layer gradually decreases along the growth direction of the first structural layer.

6. The LED epitaxial structure according to claim 4, characterized in that: The Al component in the third structural layer gradually decreases along the growth direction of the third structural layer.

7. The LED epitaxial structure according to claim 1, characterized in that: The first-type semiconductor layer includes a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer and a first-type barrier layer, wherein the first-type ohmic contact layer is located between the corrosion stop layer and the first-type window layer, and the first-type barrier layer is located between the first-type confinement layer and the active layer.

8. The LED epitaxial structure according to claim 1, characterized in that: The first-type semiconductor layer is an n-type semiconductor layer, and the second-type semiconductor layer is a p-type semiconductor layer.

9. The LED epitaxial structure according to claim 1, characterized in that: The substrate includes a GaAs substrate or a Si substrate.

10. A method for preparing an LED epitaxial structure, characterized in that: The following steps are involved: providing a substrate; Growing a bottom buffer layer, an etching stop layer, a first type semiconductor layer and an active layer in sequence on the substrate; A second-type semiconductor layer is grown on the active layer, wherein the second-type semiconductor layer includes, from bottom to top, a second-type barrier layer, a second-type confinement layer, a strain buffer layer, a second-type current spreading layer, and a second-type ohmic contact layer, and the strain buffer layer is a single-period structure or a multi-period structure, and each period of the strain buffer layer includes a first structure layer, a second structure layer, and a third structure layer stacked in sequence, wherein the material of the first structure layer includes (Al x Ga 1-x ) 0.5 In 0.5 P; the material of the second structural layer includes GaP; the material of the third structural layer includes (Al y Ga 1-y ) 0.5 In 0.5 P, where 0.10≤x≤0.50, 0.05≤y≤0.

10.

11. The method for preparing an LED epitaxial structure according to claim 10, characterized in that: The thickness of the strain buffer layer is 50nm-120nm, wherein the total thickness of the first structural layer in all periods is 10nm-30nm, the total thickness of the second structural layer in all periods is 30nm-60nm, and the total thickness of the third structural layer in all periods is 10nm-30nm.

12. The method for preparing an LED epitaxial structure according to claim 10, characterized in that: The first structure layer, the second structure layer and the third structure layer are all doped with Mg, and the doping concentration of Mg is 1E18cm -3 ~5E18 cm -3 .

13. The method for preparing an LED epitaxial structure according to claim 10, characterized in that: The Al compositions in the first structural layer and the third structural layer are graded.

14. The method for preparing an LED epitaxial structure according to claim 13, characterized in that: The Al component in the first structural layer gradually decreases along the growth direction of the first structural layer.

15. The method for preparing an LED epitaxial structure according to claim 13, characterized in that: The Al component in the third structural layer gradually decreases along the growth direction of the third structural layer.

16. The method for preparing an LED epitaxial structure according to claim 10, characterized in that: The first-type semiconductor layer includes a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer and a first-type barrier layer, wherein the first-type ohmic contact layer is located between the corrosion stop layer and the first-type window layer, and the first-type barrier layer is located between the first-type confinement layer and the active layer.

17. The method for preparing an LED epitaxial structure according to claim 10, characterized in that: The first-type semiconductor layer is an n-type semiconductor layer, and the second-type semiconductor layer is a p-type semiconductor layer.

18. The method for preparing an LED epitaxial structure according to claim 10, characterized in that: The substrate includes a GaAs substrate or a Si substrate.

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