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 distributed Bragg reflector layer, a first-type semiconductor layer, an active layer, and a second-type semiconductor layer, wherein the distributed Bragg reflector layer comprises, from bottom to top, a first distributed Bragg reflector layer, a transition layer, and a second distributed Bragg reflector layer, wherein the first distributed Bragg reflector layer is a periodic structure in which a first AlAs layer and an AlGaAsP layer are alternately arranged; and the second distributed Bragg reflector layer is a periodic structure in which a second AlAs layer and an AlGaAs layer are alternately arranged. The present invention can reduce the high warpage of the epitaxial structure caused by the high period number of the distributed Bragg reflector layer through the structural setting of the distributed Bragg reflector layer, and reduce the risk of scratches and fragments in the subsequent chip manufacturing process.

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 electronic component that can emit light. 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. For example, it can be used in indoor and outdoor lighting, traffic lights, backlight sources and other fields.

[0003] In order to improve the brightness of existing LEDs, a DBR layer (distributed Bragg reflection) is usually grown between the substrate and the active layer. The DBR layer is a periodic structure composed of two materials with different refractive indices arranged alternately, and the optical thickness of each layer of material is 1 / 4n of the central reflection wavelength (n is the refractive index of each layer of material).

[0004] Usually, the DBR layer uses a low-refractive-index AlAs layer and a high-refractive-index AlGaAs layer arranged alternately to form a periodic structure. Since these two materials have a large lattice mismatch with the AlGaInP system commonly used in red and yellow LEDs, and the periodic structure will amplify this lattice mismatch, the number of periods of the DBR layer should generally not be too high. However, due to the low luminous intensity of yellow LEDs, a high-period DBR layer is usually required to obtain high-brightness yellow LEDs, resulting in a large warpage of the epitaxial structure itself. During the chip manufacturing process, this warpage can easily cause scratches or even fragments on the chip surface, greatly reducing the yield of finished products.

[0005] Therefore, it is necessary to provide an LED epitaxial structure and a preparation method to reduce the warping of the epitaxial structure caused by the high number of cycles of the DBR layer. Summary of the invention

[0006] The purpose of the present invention is to provide an LED epitaxial structure and a preparation method to reduce the high warping of the epitaxial structure caused by the high number of cycles of the DBR layer, reduce the risk of scratches and fragments in the subsequent chip manufacturing process, and improve the finished product yield.

[0007] 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 located on a substrate, a distributed Bragg reflector layer, a first-type semiconductor layer, an active layer and a second-type semiconductor layer, wherein the distributed Bragg reflector layer comprises, from bottom to top, a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer, wherein the first distributed Bragg reflector layer is a periodic structure in which a first AlAs layer and an AlGaAsP layer are alternately arranged; and the second distributed Bragg reflector layer is a periodic structure in which a second AlAs layer and an AlGaAs layer are alternately arranged.

[0008] Optionally, in the LED epitaxial structure, the material of the first AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAsP layer includes (Al x Ga 1-x ) 0.5 As 0.3 P 0.2 , wherein 0.5≤x≤0.8; the material of the second AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAs layer includes (Al y Ga 1-y ) 0.5 As 0.5 , where 0.5≤y≤0.8.

[0009] Optionally, in the LED epitaxial structure, the optical thickness of each layer of material in the first distributed Bragg reflector layer and the second distributed Bragg reflector layer is 1 / 4n of the central reflection wavelength, where n is the refractive index of each layer of material.

[0010] Optionally, in the LED epitaxial structure, the period number of the first distributed Bragg reflector layer is less than half of the total period number of the distributed Bragg reflector layer, and the period number of the second distributed Bragg reflector layer is greater than half of the total period number of the distributed Bragg reflector layer.

[0011] Optionally, in the LED epitaxial structure, the number of periods of the first distributed Bragg reflector layer is one quarter of the total number of periods of the distributed Bragg reflector layers, and the number of periods of the second distributed Bragg reflector layer is three quarters of the total number of periods of the distributed Bragg reflector layers.

[0012] Optionally, in the LED epitaxial structure, the material of the transition layer includes (Al a Ga 1-a )0.5 As 0.5-b P b , where 0.5≤a≤1, 0≤b≤0.2.

[0013] Optionally, in the LED epitaxial structure, the Al component in the transition layer gradually changes from x to 1 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer; the P component in the transition layer gradually changes from 0.2 to 0 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer.

[0014] Optionally, in the LED epitaxial structure, the thickness of the transition layer is 10 nm to 50 nm.

[0015] Optionally, in the LED epitaxial structure, the distributed Bragg reflector layer is doped with Si, and the doping concentration is 1E18cm -3 ~1E19cm -3 .

[0016] Optionally, in the LED epitaxial structure, the first-type semiconductor layer includes, from bottom to top, a first-type confinement layer and a first barrier layer.

[0017] Optionally, in the LED epitaxial structure, the second-type semiconductor layer includes, from bottom to top, a second barrier layer, a second confinement layer, a second window layer and a second ohmic contact layer.

[0018] 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:

[0019] providing a substrate;

[0020] A bottom buffer layer and a distributed Bragg reflector layer are sequentially grown on the substrate, wherein the distributed Bragg reflector layer comprises, from bottom to top, a first distributed Bragg reflector layer, a transition layer, and a second distributed Bragg reflector layer, the first distributed Bragg reflector layer is a periodic structure in which a first AlAs layer and an AlGaAsP layer are alternately arranged; and the second distributed Bragg reflector layer is a periodic structure in which a second AlAs layer and an AlGaAs layer are alternately arranged;

[0021] A first-type semiconductor layer, an active layer and a second-type semiconductor layer are sequentially grown on the distributed Bragg reflector layer.

[0022] Optionally, in the method for preparing the LED epitaxial structure, the material of the first AlAs layer includes Al 0.5 As 0.5; The material of the AlGaAsP layer includes (Al x Ga 1-x ) 0.5 As 0.3 P 0.2 , wherein 0.5≤x≤0.8; the material of the second AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAs layer includes (Al y Ga 1-y ) 0.5 As 0.5 , where 0.5≤y≤0.8.

[0023] Optionally, in the method for preparing the LED epitaxial structure, the optical thickness of each layer of material in the first distributed Bragg reflector layer and the second distributed Bragg reflector layer is 1 / 4n of the central reflection wavelength, where n is the refractive index of each layer of material.

[0024] Optionally, in the method for preparing the LED epitaxial structure, the number of periods of the first distributed Bragg reflector layer is less than half of the total number of periods of the distributed Bragg reflector layer, and the number of periods of the second distributed Bragg reflector layer is greater than half of the total number of periods of the distributed Bragg reflector layer.

[0025] Optionally, in the method for preparing the LED epitaxial structure, the number of periods of the first distributed Bragg reflector layer is one quarter of the total number of periods of the distributed Bragg reflector layer, and the number of periods of the second distributed Bragg reflector layer is three quarters of the total number of periods of the distributed Bragg reflector layer.

[0026] Optionally, in the method for preparing the LED epitaxial structure, the material of the transition layer includes (Al a Ga 1-a ) 0.5 As 0.5-b P b , where 0.5≤a≤1, 0≤b≤0.2.

[0027] Optionally, in the method for preparing the LED epitaxial structure, the Al component in the transition layer gradually changes from x to 1 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer; the P component in the transition layer gradually changes from 0.2 to 0 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer.

[0028] Optionally, in the method for preparing the LED epitaxial structure, the thickness of the transition layer is 10 nm to 50 nm.

[0029] Optionally, in the method for preparing the LED epitaxial structure, the distributed Bragg reflector layer is doped with Si, and the doping concentration is 1E18 cm -3 ~1E19cm -3 .

[0030] Optionally, in the method for preparing the LED epitaxial structure, the first-type semiconductor layer includes, from bottom to top, a first-type confinement layer and a first barrier layer.

[0031] Optionally, in the method for preparing the LED epitaxial structure, the second-type semiconductor layer includes, from bottom to top, a second barrier layer, a second confinement layer, a second window layer, and a second ohmic contact layer.

[0032] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0033] The first distributed Bragg reflector layer of the present invention is a periodic structure in which first AlAs layers and AlGaAsP layers are alternately arranged, and the second distributed Bragg reflector layer is a periodic structure in which second AlAs layers and AlGaAs layers are alternately arranged. The first distributed Bragg reflector layer and the second distributed Bragg reflector layer together constitute a distributed Bragg reflector layer, which can balance the high warping caused by a distributed Bragg reflector layer with a high period number, while taking into account the high reflectivity required by the distributed Bragg reflector layer.

[0034] Moreover, the present invention arranges a transition layer between the first distributed Bragg reflector layer and the second distributed Bragg reflector layer. The transition layer is a structural layer with a gradient of Al component, Ga component, P component and As component, which can be beneficial to the release of stress and reduce the generation of defects, thereby ensuring the growth quality of the distributed Bragg reflector layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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.

[0036] Figure 1 is a schematic structural diagram of an LED epitaxial structure according to an embodiment of the present invention;

[0037] Figure 2 is a schematic structural diagram of a first distributed Bragg reflector layer according to an embodiment of the present invention;

[0038] Figure 3is a schematic structural diagram of a second distributed Bragg reflector layer according to an embodiment of the present invention;

[0039] Figure 4 is a flow chart of a method for preparing an LED epitaxial structure according to an embodiment of the present invention;

[0040] Figure 1 middle:

[0041] 10-substrate, 20-epitaxial structure, 201-bottom buffer layer, 202-first distributed Bragg reflector layer, 203-transition layer, 204-second distributed Bragg reflector layer, 205-first type confinement layer, 206-first barrier layer, 207-active layer, 208-second barrier layer, 209-second type confinement layer, 210-second type window layer, 211-second type ohmic contact layer;

[0042] Figure 2 middle:

[0043] 2021 - first AlAs layer, 2022 - AlGaAsP layer;

[0044] Figure 3 middle:

[0045] 2041 - second AlAs layer, 2042 - AlGaAs layer. DETAILED DESCRIPTION

[0046] 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.

[0047] Before describing the embodiments of the present invention, the following contents are described in advance: First, in this specification, when simply indicated as "AlGaAs", it means an arbitrary compound in which the chemical composition ratio of the sum of Al and Ga to As is 1:1 and the ratio of Al to Ga is not fixed.

[0048] Figure 1 A schematic diagram of the structure of an LED epitaxial structure is shown. Figure 1 The LED epitaxial structure 20 includes, from bottom to top, a bottom buffer layer 201 located on the substrate 10, a distributed Bragg reflector layer, a first-type semiconductor layer, an active layer 207 and a second-type semiconductor layer.

[0049] The distributed Bragg reflector layer includes, from bottom to top, a first distributed Bragg reflector layer 202 , a transition layer 203 and a second distributed Bragg reflector layer 204 .

[0050] See also Figure 2 and Figure 3 The first distributed Bragg reflector layer 202 is a periodic structure in which first AlAs layers 2021 and AlGaAsP layers 2022 are alternately arranged; the second distributed Bragg reflector layer 204 is a periodic structure in which second AlAs layers 2041 and AlGaAs layers 2042 are alternately arranged.

[0051] The first-type semiconductor layer includes, from bottom to top, a first-type confinement layer 205 and a first barrier layer 206. In other embodiments, the first-type semiconductor layer may further include a first-type ohmic contact layer and a first-type window layer between the first-type confinement layer 205 and the distributed Bragg reflector layer.

[0052] The second-type semiconductor layer includes, from bottom to top, a second barrier layer 208, a second-type confinement layer 209, a second-type window layer 210, and a second-type ohmic contact layer 211. The first barrier layer 206 and the second barrier layer 208 are undoped structural layers.

[0053] 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 confinement layer and a first barrier layer stacked in sequence. The p-type semiconductor layer includes a second barrier layer, a p-type confinement layer, a p-type window layer, and a p-type ohmic contact layer stacked in sequence.

[0054] See also Figure 4 The method for preparing the LED epitaxial structure 20 specifically includes the following steps:

[0055] Step S1: providing a substrate;

[0056] Step S2: sequentially growing a bottom buffer layer and a distributed Bragg reflector layer on the substrate, wherein the distributed Bragg reflector layer comprises, from bottom to top, a first distributed Bragg reflector layer, a transition layer, and a second distributed Bragg reflector layer, the first distributed Bragg reflector layer being a periodic structure in which a first AlAs layer and an AlGaAsP layer are alternately arranged; the second distributed Bragg reflector layer being a periodic structure in which a second AlAs layer and an AlGaAs layer are alternately arranged;

[0057] Step S3: sequentially growing a first-type semiconductor layer, an active layer and a second-type semiconductor layer on the distributed Bragg reflector layer.

[0058] The preparation process of the LED epitaxial structure is any one of metal organic chemical vapor deposition (MOCVD) process, molecular beam epitaxy (MBE) process, ultra-high vacuum chemical vapor deposition (UHVCVD), hydride vapor phase epitaxy (HVPE) process, plasma enhanced chemical vapor deposition (PECVD) and sputtering, preferably MOCVD process. In the following specific embodiments, MOCVD process is used as an example for description.

[0059] In step S1 , the substrate 10 is preferably a GaAs (gallium arsenide) substrate, and may also be a Si (silicon) substrate, but is not limited thereto.

[0060] In step S2, a bottom buffer layer 201 is grown on the substrate 10. The thickness of the bottom buffer layer 201 is preferably 100 nm to 500 nm. For example, a bottom buffer layer 201 with a thickness of 200 nm is grown in a reaction chamber of a MOCVD growth furnace. The bottom buffer layer 201 is preferably made of GaAs, but is not limited thereto.

[0061] After the bottom buffer layer 201 is grown, a distributed Bragg reflector layer is grown on the bottom buffer layer 201 . The distributed Bragg reflector layer includes a first distributed Bragg reflector layer 202 , a transition layer 203 , and a second distributed Bragg reflector layer 204 from bottom to top.

[0062] The total number of periods of the distributed Bragg reflector layer is preferably in the range of 32 to 80. The thickness of each layer in the first distributed Bragg reflector layer 202 and the second distributed Bragg reflector layer 204 is 1 / 4n of the reflection center wavelength (n is the refractive index of each layer of material, in the yellow light band, n AlAs =3.2, n AlGaAs =3.9). The distributed Bragg reflector layer 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 is not limited thereto. Furthermore, the first-type dopant is preferably Si.

[0063] The first distributed Bragg reflector layer 202 is grown on the bottom buffer layer 201, and the first distributed Bragg reflector layer 202 is a periodic structure in which first AlAs layers 2021 and AlGaAsP layers 2022 are alternately arranged. The number of periods of the first distributed Bragg reflector layer 202 is less than half of the total number of periods of the distributed Bragg reflector layer, and in order to take into account both high reflectivity and low warpage, the number of periods of the first distributed Bragg reflector layer 202 is preferably one-quarter of the total number of periods of the distributed Bragg reflector layer, that is, the number of periods of the first distributed Bragg reflector layer 202 is preferably 8-20.

[0064] The first distributed Bragg reflector layer 202 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 is not limited thereto. Further, the first-type dopant is preferably Si. The concentration of the first-type dopant doped in the first distributed Bragg reflector layer 202 is preferably 1E18 cm -3 ~1E19cm -3 .

[0065] The material of the first AlAs layer 2021 includes Al 0.5 As 0.5 , but not limited thereto. The material of the AlGaAsP layer 2022 includes (Al x Ga 1-x ) 0.5 As 0.3 P 0.2 , where 0.5≤x≤0.8. The optical thickness of each layer of material in the first distributed Bragg reflector layer 202 is 1 / 4n of the central reflection wavelength, where n is the refractive index of each layer of material. In the yellow light band, n AlAs =3.2, the refractive index of AlGaAsP is affected by the Al component. The higher the Al component, the lower the refractive index. AlGaAsP The range of is 3.8 to 3.1. Further, in each period of the first distributed Bragg reflector layer 202, a first AlAs layer 2021 with a thickness of 30 nm to 50 nm and an AlGaAsP layer 2022 with a thickness of 20 nm to 60 nm are grown. For example, in the reaction chamber of an MOCVD growth furnace, a 46 nm thick Al 0.5 As 0.5 and 45nm thickness (Al 0.7 Ga 0.3 ) 0.5 As 0.3 P 0.2 The first distributed Bragg reflector layer 202 is alternately arranged in ABAB manner to form 18 periods.

[0066] The thickness of the transition layer 203 is preferably 10 nm to 50 nm, and the transition layer 203 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 is not limited thereto. Further, the first-type dopant is preferably Si. The concentration of the first-type dopant doped in the transition layer 203 is preferably 1E18 cm -3 ~1E19cm -3 .

[0067] The transition layer 203 is a layer with a gradient structure of Al, Ga, P (phosphorus) and As components. The material of the transition layer 203 is preferably (Al a Ga 1-a ) 0.5 As 0.5-b P b , 0.5≤a≤1, 0≤b≤0.2, along the direction from the first distributed Bragg reflector layer 202 to the second distributed Bragg reflector layer 204, the Al component a gradually changes from x to 1, and the P component b gradually changes from 0.2 to 0. For example, a transition layer 203 with a thickness of 20 nm is grown in the reaction chamber of an MOCVD growth furnace. The transition layer 203 is initially grown (Al 0.7 Ga 0.3 ) 0.5 As 0.3 P 0.2 Then the Al component changes from 0.7 to 1 from the beginning to the end of growth, the P component changes from 0.2 to 0 from the beginning to the end of growth, and the As component changes from 0.3 to 0.5 from the beginning to the end of growth, that is, the transition layer 203 is Al when the growth ends. 0.5 As 0.5 .

[0068] In this embodiment, the lattice constant of the material of the transition layer 203 is initially close to that of the material of the first distributed Bragg reflector layer 202, and then gradually changes to be close to that of the second distributed Bragg reflector layer 202, which can better release the mismatch stress between the first distributed Bragg reflector layer 202 and the second distributed Bragg reflector layer 202 and improve the crystal quality.

[0069] After the transition layer 203 is grown, the second distributed Bragg reflector layer 204 is grown on the transition layer 203. The second distributed Bragg reflector layer 204 is a periodic structure in which second AlAs layers 2041 and AlGaAs layers 2042 are alternately arranged. The number of periods of the second distributed Bragg reflector layer 204 is greater than half of the total number of periods of the distributed Bragg reflector layer. In order to take into account both high reflectivity and low warpage, the number of periods of the second distributed Bragg reflector layer 204 is preferably three quarters of the total number of periods of the distributed Bragg reflector layer, that is, the number of periods of the second distributed Bragg reflector layer 204 is preferably 24 to 60.

[0070] The first type dopant, such as n-type dopant, doped in the second distributed Bragg reflector layer 204 may be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Further, the first type dopant is preferably Si. The concentration of the first type dopant doped in the second distributed Bragg reflector layer 204 is preferably 1E18 cm -3 ~1E19cm -3 .

[0071] The material of the second AlAs layer 2041 includes Al 0.5 As 0.5 , but not limited thereto. The material of the AlGaAs layer 2042 includes (Al y Ga 1-y ) 0.5 As 0.5 , where 0.5≤y≤0.8. The Al component in the material of the AlGaAs layer 2042 is preferably the same as the Al component in the AlGaAsP layer 2022, that is, y=x. The optical thickness of each layer of material in the second distributed Bragg reflector layer 204 is 1 / 4n of the central reflection wavelength, where n is the refractive index of each layer of material. In the yellow light band, n AlAs =3.2, n AlGaAs =3.9. Further, in each period of the second distributed Bragg reflector layer 204, a second AlAs layer 2041 with a thickness of 30nm to 50nm and an AlGaAs layer 2042 with a thickness of 20nm to 60nm are grown. For example, in the reaction chamber of an MOCVD growth furnace, a 46nm thick Al 0.5 As 0.5 and 38nm thickness (Al 0.7 Ga 0.3 ) 0.5 As 0.5 The second distributed Bragg reflector layer 204 is alternately arranged in an ABAB manner to form 54 periods.

[0072] In the prior art, since the lattice constants of the active layer AlGaInP and the second-type window layer GaP are smaller than those of AlAs and AlGaAs, the larger lattice mismatch leads to a larger tensile strain during the growth process, and the more the number of periods of the DBR (distributed Bragg reflector layer), the greater the strain, and the greater the warpage of the epitaxial structure. If AlAs and AlGaAsP are used as the material of the DBR, the addition of P (phosphorus) can make the lattice constant smaller to balance the lattice difference between the DBR and AlGaInP systems. However, the reflection effect of the structure composed of AlAs and AlGaAsP as a reflector is not as good as that of the structure composed of AlAs and AlGaAs, which is contrary to the original intention of obtaining a high-brightness yellow LED. The present embodiment adopts a structure composed of AlAs and AlGaAs (i.e., the second distributed Bragg reflector layer) and a structure composed of AlAs and AlGaAsP (the first distributed Bragg reflector layer) to form a hybrid distributed Bragg reflector layer structure, that is, by changing a part of the periodic structure composed of AlAs and AlGaAs to a structure composed of AlAs and AlGaAsP, the high warping caused by the distributed Bragg reflector layer with a high period number is balanced, while taking into account the high reflectivity required by the distributed Bragg reflector layer.

[0073] Due to the difference in lattice constants between the first distributed Bragg reflector layer and the second distributed Bragg reflector layer, growing the second distributed Bragg reflector layer directly on the first distributed Bragg reflector layer is likely to cause the crystal quality of the second distributed Bragg reflector layer to deteriorate. In this embodiment, a transition layer is designed between the first distributed Bragg reflector layer and the second distributed Bragg reflector layer. The material of the transition layer is a structural layer with a gradient of Al component, Ga component, P component and As component, which can be beneficial to the release of mismatch stress and reduce the generation of defects, thereby ensuring the growth quality of the distributed Bragg reflector layer.

[0074] In this embodiment, the second distributed Bragg reflector layer 204 is a periodic structure in which second AlAs layers 2041 and AlGaAs layers 2042 are alternately arranged, and the first distributed Bragg reflector layer 202 is a periodic structure in which first AlAs layers 2021 and AlGaAsP layers 2022 are alternately arranged. The reflectivity of the second distributed Bragg reflector layer 204 is higher than that of the first distributed Bragg reflector layer 202, and its absorption of light is lower than that of the first distributed Bragg reflector layer 202. The second distributed Bragg reflector layer 204 is arranged on a side closer to the active layer 207, so that more light emitted by the active layer 207 can be reflected, thereby improving the reflectivity of the distributed Bragg reflector layer, and thus improving the luminous efficiency of the LED epitaxial structure.

[0075] In step S3, after the distributed Bragg reflector layer is grown, a first-type semiconductor layer is grown on the distributed Bragg reflector layer. The first-type semiconductor layer includes a first-type confinement layer 205 and a first barrier layer 206 from bottom to top.

[0076] After growing the distributed Bragg reflector layer, a first type confinement layer 205 is grown on the distributed Bragg reflector layer. The first type confinement layer 205 is used to provide electrons. The thickness of the first type confinement layer 205 is preferably 300nm to 800nm. The preferred material of the first type confinement layer 205 is AlInP, but not limited thereto. For example, a first type confinement layer 205 with a thickness of 400nm is grown in the reaction chamber of an MOCVD growth furnace. The first type confinement layer 205 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.

[0077] After the first type confinement layer 205 is grown, a first barrier layer 206 is grown on the first type confinement layer 205. The thickness of the first barrier layer 206 is preferably 50 nm to 200 nm. For example, a first barrier layer 206 with a thickness of 100 nm is grown in a reaction chamber of a MOCVD growth furnace. The first barrier layer 206 is preferably made of AlGaInP, but is not limited thereto. The first barrier layer is an undoped structural layer.

[0078] After the first barrier layer 206 is grown, the active layer 207 is grown on the first barrier layer 206. The material of the active layer 207 is preferably AlGaInP, and its thickness is preferably 300nm to 600nm, for example, 400nm. The active layer 207 is preferably a multi-quantum well structure, that is, the active layer 207 is preferably a periodic structure composed of quantum wells and quantum barriers, and the number of periods of the active layer 207 is preferably 30 to 80. For example, 40 periods of the active layer 207 are grown in the reaction chamber of the MOCVD growth furnace.

[0079] After the active layer 207 is grown, a second-type semiconductor layer is grown on the active layer 207. The second-type semiconductor layer includes, from bottom to top, a second barrier layer 208, a second-type confinement layer 209, a second-type window layer 210, and a second-type ohmic contact layer 211.

[0080] Therefore, after the active layer 207 is grown, a second barrier layer 208 is grown on the active layer 207. The second barrier layer 208 is preferably made of AlGaInP, but is not limited thereto. The second barrier layer is an undoped structural layer.

[0081] The thickness of the second barrier layer 208 is preferably 100 nm to 300 nm. For example, the second barrier layer 208 with a thickness of 200 nm is grown in the reaction chamber of a MOCVD growth furnace.

[0082] After the second barrier layer 208 is grown, a second type confinement layer 209 is grown on the second barrier layer 208. The second type confinement layer 209 is used to provide holes. Moreover, the first type confinement layer 205 and the second type confinement layer 209 as confinement layers have two main functions: on the one hand, they provide electron-hole pairs to enter the active layer 207 for composite light emission; on the other hand, they restrict minority carriers from overflowing the active layer 207, thereby improving the composite light emission efficiency.

[0083] The material of the second type confinement layer 209 is preferably AlInP, but not limited thereto. The second type confinement layer 209 is doped with a second type dopant, 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.

[0084] The thickness of the second type confinement layer 209 is preferably 200 nm to 600 nm. For example, the second type confinement layer 209 with a thickness of 400 nm is grown in the reaction chamber of a MOCVD growth furnace.

[0085] After growing the second-type confinement layer 209, a second-type window layer 210 is grown on the second-type confinement layer 209. The second-type window layer 210 is used for current expansion to prevent uneven current distribution on the device. The material of the second-type window layer 210 is preferably GaP, but not limited thereto. The doping source of the second-type window layer 210 is preferably Mg, but not limited thereto. The thickness of the second-type window layer 210 is preferably 500nm to 1500nm. For example, a second-type window layer 210 with a thickness of 1000nm is grown in the reaction chamber of an MOCVD growth furnace.

[0086] After the second-type window layer 210 is grown, the second-type ohmic contact layer 211 is grown on the second-type window layer 210. The second-type ohmic contact layer 211 is used to form an ohmic contact with a metal electrode. The material of the second-type ohmic contact layer 211 is preferably GaP, but not limited thereto. The second-type ohmic contact layer 211 may be doped with carbon (C).

[0087] The thickness of the second-type ohmic contact layer 211 is preferably 100 nm to 250 nm. For example, the second-type ohmic contact layer 211 with a thickness of 200 nm is grown in a reaction chamber of a MOCVD growth furnace.

[0088] The first distributed Bragg reflector layer of the present invention is a periodic structure in which first AlAs layers and AlGaAsP layers are alternately arranged, and the second distributed Bragg reflector layer is a periodic structure in which second AlAs layers and AlGaAs layers are alternately arranged. The first distributed Bragg reflector layer and the second distributed Bragg reflector layer together constitute a distributed Bragg reflector layer, which can balance the high warping caused by a distributed Bragg reflector layer with a high period number, while taking into account the high reflectivity required by the distributed Bragg reflector layer.

[0089] Moreover, the present invention arranges a transition layer between the first distributed Bragg reflector layer and the second distributed Bragg reflector layer. The transition layer is a structural layer with a gradient of Al component, Ga component, P component and As component, which can be beneficial to the release of stress and reduce the generation of defects, thereby ensuring the growth quality of the distributed Bragg reflector layer.

[0090] 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.

[0091] It should also be understood that the present invention is not limited to the specific methods, compounds, materials, manufacturing techniques, usages and applications described herein, which may vary. It should also be understood that the terms described herein are only used to describe specific embodiments, rather than to limit the scope of the present invention. It must be noted that the singular forms "one", "a kind" and "the" used herein and in the appended claims include plural references unless the context clearly indicates the opposite meaning. Thus, for example, a reference to "a step" means a reference to one or more steps, and may include secondary steps. All conjunctions used should be understood in the broadest sense. Therefore, the word "or" should be understood to have the definition of a logical "or", rather than a logical "exclusive or", unless the context clearly indicates the opposite meaning. The structure described herein will be understood to also quote the functional equivalent of the structure. Language that can be interpreted as approximate should be understood as such, unless the context clearly indicates the opposite meaning.

Claims

1. An LED epitaxial structure, characterized in that: The LED epitaxial structure comprises, from bottom to top, a bottom buffer layer located on a substrate, a distributed Bragg reflector layer, a first-type semiconductor layer, an active layer, and a second-type semiconductor layer, wherein the distributed Bragg reflector layer comprises, from bottom to top, a first distributed Bragg reflector layer, a transition layer, and a second distributed Bragg reflector layer, wherein the first distributed Bragg reflector layer is a periodic structure in which a first AlAs layer and an AlGaAsP layer are alternately arranged; the second distributed Bragg reflector layer is a periodic structure in which a second AlAs layer and an AlGaAs layer are alternately arranged, and the material of the transition layer comprises (Al a Ga 1-a ) 0.5 As 0.5-b P b , where 0.5≤a≤1, 0≤b≤0.

2.

2. The LED epitaxial structure according to claim 1, characterized in that: The material of the first AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAsP layer includes (Al x Ga 1-x ) 0.5 As 0.3 P 0.2 , wherein 0.5≤x≤0.8; the material of the second AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAs layer includes (Al y Ga 1-y ) 0.5 As 0.5 , where 0.5≤y≤0.

8.

3. The LED epitaxial structure according to claim 1, characterized in that: The optical thickness of each layer of material in the first distributed Bragg reflector layer and the second distributed Bragg reflector layer is 1 / 4n of the central reflection wavelength, where n is the refractive index of each layer of material.

4. The LED epitaxial structure according to claim 1, characterized in that: The period number of the first distributed Bragg reflector layer is less than one half of the total period number of the distributed Bragg reflector layer, and the period number of the second distributed Bragg reflector layer is greater than one half of the total period number of the distributed Bragg reflector layer.

5. The LED epitaxial structure according to claim 4, characterized in that: The number of periods of the first distributed Bragg reflector layer is one quarter of the total number of periods of the distributed Bragg reflector layer, and the number of periods of the second distributed Bragg reflector layer is three quarters of the total number of periods of the distributed Bragg reflector layer.

6. The LED epitaxial structure according to claim 2, characterized in that: The Al component in the transition layer changes gradually from x to 1 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer; the P component in the transition layer changes gradually from 0.2 to 0 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer.

7. The LED epitaxial structure according to claim 1, characterized in that: The thickness of the transition layer is 10nm to 50nm.

8. The LED epitaxial structure according to claim 1, characterized in that: The distributed Bragg reflector layer is doped with Si, and the doping concentration is 1E18cm -3 ~1E19cm -3 .

9. The LED epitaxial structure according to claim 1, characterized in that: The first-type semiconductor layer includes, from bottom to top, a first-type confinement layer and a first barrier layer.

10. The LED epitaxial structure according to claim 1, characterized in that: The second-type semiconductor layer includes, from bottom to top, a second barrier layer, a second-type confinement layer, a second-type window layer and a second-type ohmic contact layer.

11. A method for preparing an LED epitaxial structure, characterized in that: The following steps are involved: providing a substrate; A bottom buffer layer and a distributed Bragg reflector layer are sequentially grown on the substrate, wherein the distributed Bragg reflector layer includes, from bottom to top, a first distributed Bragg reflector layer, a transition layer, and a second distributed Bragg reflector layer, wherein the first distributed Bragg reflector layer is a periodic structure in which a first AlAs layer and an AlGaAsP layer are alternately arranged; the second distributed Bragg reflector layer is a periodic structure in which a second AlAs layer and an AlGaAs layer are alternately arranged, and the material of the transition layer includes (Al a Ga 1-a ) 0.5 As 0.5-b P b , where 0.5≤a≤1, 0≤b≤0.2; A first-type semiconductor layer, an active layer and a second-type semiconductor layer are sequentially grown on the distributed Bragg reflector layer.

12. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The material of the first AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAsP layer includes (Al x Ga 1-x ) 0.5 As 0.3 P 0.2 , wherein 0.5≤x≤0.8; the material of the second AlAs layer includes Al 0.5 As 0.5 ; The material of the AlGaAs layer includes (Al y Ga 1-y ) 0.5 As 0.5 , where 0.5≤y≤0.

8.

13. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The optical thickness of each layer of material in the first distributed Bragg reflector layer and the second distributed Bragg reflector layer is 1 / 4n of the central reflection wavelength, where n is the refractive index of each layer of material.

14. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The period number of the first distributed Bragg reflector layer is less than one half of the total period number of the distributed Bragg reflector layer, and the period number of the second distributed Bragg reflector layer is greater than one half of the total period number of the distributed Bragg reflector layer.

15. The method for preparing an LED epitaxial structure according to claim 14, characterized in that: The number of periods of the first distributed Bragg reflector layer is one quarter of the total number of periods of the distributed Bragg reflector layer, and the number of periods of the second distributed Bragg reflector layer is three quarters of the total number of periods of the distributed Bragg reflector layer.

16. The method for preparing an LED epitaxial structure according to claim 12, wherein: The Al component in the transition layer changes gradually from x to 1 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer; the P component in the transition layer changes gradually from 0.2 to 0 along the direction from the first distributed Bragg reflector layer to the second distributed Bragg reflector layer.

17. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The thickness of the transition layer is 10nm to 50nm.

18. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The distributed Bragg reflector layer is doped with Si, and the doping concentration is 1E18cm -3 ~1E19cm -3 .

19. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The first-type semiconductor layer includes, from bottom to top, a first-type confinement layer and a first barrier layer.

20. The method for preparing an LED epitaxial structure according to claim 11, characterized in that: The second-type semiconductor layer includes, from bottom to top, a second barrier layer, a second-type confinement layer, a second-type window layer and a second-type ohmic contact layer.

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