CN115000259A - LED epitaxial structure and preparation method thereof - Google Patents

LED epitaxial structure and preparation method thereof Download PDF

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Publication number
CN115000259A
CN115000259A CN202210556941.8A CN202210556941A CN115000259A CN 115000259 A CN115000259 A CN 115000259A CN 202210556941 A CN202210556941 A CN 202210556941A CN 115000259 A CN115000259 A CN 115000259A
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layer
distributed bragg
bragg reflector
epitaxial structure
led epitaxial
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赖玉财
李森林
毕京锋
谢岚驰
廖寅生
薛龙
王亚宏
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Xiamen Silan Advanced Compound Semiconductor Co Ltd
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Xiamen Silan Advanced Compound Semiconductor Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/10—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a light reflecting structure, e.g. semiconductor Bragg reflector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table

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  • Led Devices (AREA)

Abstract

The invention provides an LED epitaxial structure and a preparation method thereof, wherein the LED epitaxial structure sequentially comprises the following components from bottom to top: the distributed Bragg reflector comprises a bottom buffer layer, 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 sequentially comprises a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer from bottom to top; the second distributed Bragg reflector layer is of a periodic structure in which second AlAs layers and AlGaAs layers are arranged alternately. According to the invention, through the structural arrangement of the distributed Bragg reflector layer, the high warping degree of the epitaxial structure caused by the high periodicity of the distributed Bragg reflector layer can be reduced, and the risks of scratching and fragmenting in the subsequent chip manufacturing process are reduced.

Description

LED epitaxial structure and preparation method thereof
Technical Field
The invention belongs to the technical field of LED epitaxial growth, and particularly relates to an LED epitaxial structure and a preparation method thereof.
Background
A Light Emitting Diode (LED) is a semiconductor electronic component capable of Emitting Light. In recent years, LEDs have been widely used due to their advantages of low power consumption, long life, small size, energy saving, environmental protection, and the like, and may be applied to the fields of indoor and outdoor lighting, traffic lights, backlights, and the like.
In order to improve the light emitting brightness of the existing LED, a Distributed Bragg Reflector (DBR) layer is generally grown between a substrate and an active layer, wherein the DBR layer is a periodic structure formed by alternately arranging two materials with different refractive indexes, and the optical thickness of each material is 1/4n (n is the refractive index of each material) of the central reflection wavelength.
The number of DBR layers is generally not high because of the large lattice mismatch between the low index AlAs layers and the high index AlGaAs layers that are typically used in red and yellow LEDs, and because the periodic structure amplifies this lattice mismatch. However, since the yellow LED has low light emitting intensity, the DBR layer with high cycle number is usually required to obtain a high-brightness yellow LED, so that the epitaxial structure has a large warpage, and when a chip is manufactured, the warpage easily causes scratches or even chips on the chip surface, and the yield of the finished product is greatly reduced.
Therefore, there is a need for an LED epitaxial structure and a method for fabricating the same that reduces warpage of the epitaxial structure due to high periodicity of DBR layers.
Disclosure of Invention
The invention aims to provide an LED epitaxial structure and a preparation method thereof, which are used for reducing the high warping degree of the epitaxial structure caused by the high periodicity of a DBR layer, reducing the risks of scratching and fragmenting in the subsequent chip manufacturing process and improving the yield of finished products.
In order to achieve the above and other related objects, the present invention provides an LED epitaxial structure, which includes, from bottom to top: the distributed Bragg reflector comprises a bottom buffer layer, 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 sequentially comprises a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer from bottom to top; the second distributed Bragg reflector layer is a periodic structure formed by alternately arranging second AlAs layers and AlGaAs layers.
Optionally, in the LED epitaxial structure, a material of the first AlAs layer includes Al 0.5 As 0.5 (ii) a The material of the AlGaAsP layer comprises (Al) x Ga 1-x ) 0.5 As 0.3 P 0.2 Wherein x is more than or equal to 0.5 and less than or equal to 0.8; the material of the second AlAs layer comprises Al 0.5 As 0.5 (ii) a The material of the AlGaAs layer comprises (Al) y Ga 1-y ) 0.5 As 0.5 Wherein y is more than or equal to 0.5 and less than or equal to 0.8.
Optionally, in the LED epitaxial structure, an optical thickness of each of the first distributed bragg reflector layer and the second distributed bragg reflector layer is 1/4n of a central reflection wavelength, where n is a refractive index of each layer of the material.
Optionally, in the LED epitaxial structure, the number of cycles of the first dbr layer is less than half of the total number of cycles of the dbr layer, and the number of cycles of the second dbr layer is greater than half of the total number of cycles of the dbr layer.
Optionally, in the LED epitaxial structure, the number of cycles of the first distributed bragg reflector layer is one fourth of the total number of cycles of the distributed bragg reflector layer, and the number of cycles of the second distributed bragg reflector layer is three quarters of the total number of cycles of the distributed bragg reflector layer.
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 Wherein a is more than or equal to 0.5 and less than or equal to 1, and b is more than or equal to 0 and less than or equal to 0.2.
Optionally, in the LED epitaxial structure, an Al component in the transition layer gradually changes from x to 1 along a direction in which the first distributed bragg reflector layer points to the second distributed bragg reflector layer; the P component in the transition layer is gradually changed from 0.2 to 0 along the direction of the first distributed Bragg reflector layer pointing to the second distributed Bragg reflector layer.
Optionally, in the LED epitaxial structure, the thickness of the transition layer is 10nm to 50 nm.
Optionally, in the LED epitaxial structure, the dbr layer is doped with Si at a doping concentration of 1E18cm -3 ～1E19cm -3 。
Optionally, in the LED epitaxial structure, the first type semiconductor layer sequentially includes a first type confinement layer and a first blocking layer from bottom to top.
Optionally, in the LED epitaxial structure, the second type semiconductor layer sequentially 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.
In order to achieve the above objects and other related objects, the present invention further provides a method for manufacturing an LED epitaxial structure, including the steps of:
providing a substrate;
the distributed Bragg reflector comprises a bottom buffer layer and a distributed Bragg reflector layer which sequentially grow on the substrate, wherein the distributed Bragg reflector layer sequentially comprises a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer from bottom to top, and the first distributed Bragg reflector layer is of a periodic structure formed by alternately arranging first AlAs layers and AlGaAsP layers; the second distributed Bragg reflector layer is a periodic structure formed by alternately arranging second AlAs layers and AlGaAs layers;
and growing a first type semiconductor layer, an active layer and a second type semiconductor layer on the distributed Bragg reflector layer in sequence.
Optionally, in the preparation method of the LED epitaxial structure, the material of the first AlAs layer includes Al 0.5 As 0.5 (ii) a The material of the AlGaAsP layer comprises (Al) x Ga 1-x ) 0.5 As 0.3 P 0.2 Wherein x is more than or equal to 0.5 and less than or equal to 0.8; the material of the second AlAs layer comprises Al 0.5 As 0.5 (ii) a The material of the AlGaAs layer comprises (Al) y Ga 1-y ) 0.5 As 0.5 Wherein y is more than or equal to 0.5 and less than or equal to 0.8.
Optionally, in the method for manufacturing an LED epitaxial structure, an optical thickness of each of the first distributed bragg reflector layer and the second distributed bragg reflector layer is 1/4n of a central reflection wavelength, where n is a refractive index of each layer of the material.
Optionally, in the preparation method of the LED epitaxial structure, the number of cycles of the first distributed bragg reflector layer is less than one half of the total number of cycles of the distributed bragg reflector layer, and the number of cycles of the second distributed bragg reflector layer is greater than one half of the total number of cycles of the distributed bragg reflector layer.
Optionally, in the preparation method of the LED epitaxial structure, the number of cycles of the first distributed bragg reflector layer is one fourth of the total number of cycles of the distributed bragg reflector layer, and the number of cycles of the second distributed bragg reflector layer is three quarters of the total number of cycles of the distributed bragg reflector layer.
Optionally, in the preparation method of the LED epitaxial structure, the material of the transition layer includes (Al) a Ga 1-a ) 0.5 As 0.5-b P b Wherein a is more than or equal to 0.5 and less than or equal to 1, and b is more than or equal to 0 and less than or equal to 0.2.
Optionally, in the preparation method of the LED epitaxial structure, the Al component in the transition layer is gradually changed from x to 1 along a direction in which the first distributed bragg reflector layer points to the second distributed bragg reflector layer; and the P component in the transition layer is gradually changed from 0.2 to 0 along the direction of the first distributed Bragg reflector layer pointing to the second distributed Bragg reflector layer.
Optionally, in the preparation method of the LED epitaxial structure, the thickness of the transition layer is 10nm to 50 nm.
Optionally, in the preparation method of the LED epitaxial structure, the dbr layer is doped with Si, and the doping concentration is 1E18cm -3 ～1E19cm -3 。
Optionally, in the preparation method of the LED epitaxial structure, the first type semiconductor layer sequentially includes a first type confinement layer and a first blocking layer from bottom to top.
Optionally, in the preparation method of the LED epitaxial structure, the second type semiconductor layer sequentially 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.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the first distributed Bragg reflector layer is a periodic structure formed by alternately arranging first AlAs layers and AlGaAsP layers, the second distributed Bragg reflector layer is a periodic structure formed by alternately arranging second AlAs layers and AlGaAs layers, and the first distributed Bragg reflector layer and the second distributed Bragg reflector layer jointly form the distributed Bragg reflector layer, so that high warping degree caused by the high-periodicity distributed Bragg reflector layer can be balanced, and high reflectivity required by the distributed Bragg reflector layer is considered at the same time.
In addition, the transition layer is arranged between the first distributed Bragg reflector layer and the second distributed Bragg reflector layer and is a structural layer with gradually changed Al components, Ga components, P components and As components, so that the stress can be released favorably, the defects can be reduced, and the growth quality of the distributed Bragg reflector layer can be further ensured.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an LED epitaxial structure according to an embodiment of the invention;
FIG. 2 is a schematic structural diagram of a first DBR layer according to an embodiment of the invention;
FIG. 3 is a schematic structural diagram of a second DBR layer according to an embodiment of the invention;
fig. 4 is a flow chart of a method of fabricating an LED epitaxial structure according to an embodiment of the invention;
in FIG. 1:
10-substrate, 20-epitaxial structure, 201-bottom buffer layer, 202-first distributed bragg mirror layer, 203-transition layer, 204-second distributed bragg mirror 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;
in fig. 2:
2021-first AlAs layer, 2022-AlGaAsP layer;
in fig. 3:
2041-second AlAs layer, 2042-AlGaAs layer.
Detailed Description
The LED epitaxial structure and the method for fabricating the same according to the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
Before describing embodiments according to the present invention, the following description will be made in advance. First, in the present specification, when only "AlGaAs" is used, it means that the chemical composition ratio of the sum of Al and Ga to As is 1: 1, an arbitrary compound having an unfixed ratio of Al to Ga.
Fig. 1 shows a schematic structural diagram of an LED epitaxial structure. Referring to fig. 1, the LED epitaxial structure 20 sequentially includes, from bottom to top: a bottom buffer layer 201, a distributed bragg mirror layer, a first type semiconductor layer, an active layer 207, and a second type semiconductor layer on the substrate 10.
The distributed bragg reflector layer sequentially comprises a first distributed bragg reflector layer 202, a transition layer 203 and a second distributed bragg reflector layer 204 from bottom to top.
Referring to fig. 2 and 3, the first dbr layer 202 is a periodic structure in which first AlAs layers 2021 and AlGaAsP layers 2022 are alternately arranged; the second dbr layer 204 is a periodic structure in which second AlAs layers 2041 and AlGaAs layers 2042 are alternately arranged.
The first-type semiconductor layer sequentially comprises a first-type confinement layer 205 and a first barrier layer 206 from bottom to top. 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 dbr layer.
The second type semiconductor layer sequentially comprises 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.
The polarities of the first type semiconductor layer and the second type semiconductor layer are opposite, 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. Correspondingly, the n-type semiconductor layer comprises an n-type limiting layer and a first barrier layer which are stacked in sequence. The p-type semiconductor layer comprises a second barrier layer, a p-type limiting layer, a p-type window layer and a p-type ohmic contact layer which are sequentially stacked.
Referring to fig. 4, the method for manufacturing the LED epitaxial structure 20 specifically includes the following steps:
step S1: providing a substrate;
step S2: the distributed Bragg reflector comprises a bottom buffer layer and a distributed Bragg reflector layer which sequentially grow on the substrate, wherein the distributed Bragg reflector layer sequentially comprises a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer from bottom to top, and the first distributed Bragg reflector layer is a periodic structure formed by alternately arranging a first AlAs layer and an AlGaAsP layer; the second distributed Bragg reflector layer is a periodic structure formed by alternately arranging second AlAs layers and AlGaAs layers;
step S3: and growing a first type semiconductor layer, an active layer and a second type semiconductor layer on the distributed Bragg reflector layer in sequence.
The preparation process of the LED epitaxial structure is any one of a metal organic compound chemical vapor deposition (MOCVD) process, a Molecular Beam Epitaxy (MBE) process, an ultra-high vacuum chemical vapor deposition (UHVCVD), a Hydride Vapor Phase Epitaxy (HVPE) process, a Plasma Enhanced Chemical Vapor Deposition (PECVD) process and a sputtering method, and is preferably the MOCVD process. The following specific examples will illustrate the MOCVD process.
In step S1, the substrate 10 is preferably a GaAs (gallium arsenide) substrate, but may be a Si (silicon) substrate, but is not limited thereto.
In step S2, a bottom buffer layer 201 is grown on the substrate 10. The thickness of the bottom buffer layer 201 is preferably 100nm to 500nm, and for example, the bottom buffer layer 201 is grown in a thickness of 200nm in a reaction chamber of an MOCVD growth furnace. The bottom buffer layer 201 is preferably made of GaAs, but is not limited thereto.
After the bottom buffer layer 201 is grown, a distributed bragg reflector layer is grown on the bottom buffer layer 201, and the distributed bragg reflector layer sequentially comprises a first distributed bragg reflector layer 202, a transition layer 203 and a second distributed bragg reflector layer 204 from bottom to top.
The total cycle number range of the distributed Bragg reflector layer is preferably 32-80. The first distributed Bragg reflector layer 202 and the second distributed Bragg reflector layerEach of the distributed bragg mirror layers 204 has a thickness of 1/4n reflecting a center wavelength (n is a refractive index of each layer material, and n is in the yellow band AlAs ＝3.2，n AlGaAs 3.9). The first dopant, such as an n-type dopant, doped in the distributed bragg mirror layer may be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Further, the first dopant is preferably Si.
The first distributed bragg mirror layer 202 is grown on the bottom buffer layer 201, and the first distributed bragg mirror layer 202 is a periodic structure in which first AlAs layers 2021 and AlGaAsP layers 2022 are alternately arranged. The periodicity of the first dbr layer 202 is less than one half of the total periodicity of the dbr layer, and for high reflectivity and low warpage, the periodicity of the first dbr layer 202 is preferably one quarter of the total periodicity of the dbr layer, i.e. the periodicity of the first dbr layer 202 is preferably 8-20.
The first dbr layer 202 is doped with a first dopant, such as an n-type dopant, and may be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Further, the first dopant is preferably Si. The first DBR layer 202 is preferably doped with a first dopant at a concentration of 1E18cm -3 ～1E19cm -3 。
The material of the first AlAs layer 2021 includes Al 0.5 As 0.5 But is not limited thereto. The material of the AlGaAsP layer 2022 includes (Al) x Ga 1-x ) 0.5 As 0.3 P 0.2 Wherein x is more than or equal to 0.5 and less than or equal to 0.8. The optical thickness of each layer of the first DBR layer 202 is 1/4n of the central reflection wavelength, where n is the refractive index of each layer of material, and n is the yellow wavelength band AlAs The AlGaAsP refractive index is affected by the Al component, and n is lower as the Al component is higher AlGaAsP The range of (A) is 3.8 to 3.1. Further, each circle in the first distributed bragg reflector layer 202First AlAs layer 2021 with a thickness of 30nm to 50nm and AlGaAsP layer 2022 with a thickness of 20nm to 60nm are grown. For example, in the reaction chamber of an MOCVD growth furnace, Al is 46nm thick 0.5 As 0.5 And 45nm thick (Al) 0.7 Ga 0.3 ) 0.5 As 0.3 P 0.2 The first distributed bragg mirror layers 202 are alternately arranged in 18 periods in an ABAB manner.
The thickness of the transition layer 203 is preferably 10nm to 50nm, and the first dopant, for example, the n-type dopant, doped in the transition layer 203 may be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Further, the first dopant is preferably Si. The concentration of the first dopant doped in the transition layer 203 is preferably 1E18cm -3 ～1E19cm -3 。
The transition layer 203 is a structural layer with gradually changed Al component, Ga component, P (phosphorus) component and As component. The material of the transition layer 203 is preferably (Al) a Ga 1-a ) 0.5 As 0.5-b P b A is more than or equal to 0.5 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.2, along the direction of the first distributed bragg reflector layer 202 pointing to the second distributed bragg reflector layer 204, the Al component a is gradually changed from x to 1, and the P component b is gradually changed from 0.2 to 0. For example, a transition layer 203 of 20nm thickness is grown in the reaction chamber of the MOCVD growth furnace, and the transition layer 203 is grown at the beginning (Al) 0.7 Ga 0.3 ) 0.5 As 0.3 P 0.2 Then, the Al composition is gradually changed from 0.7 to 1 from the start to the end of growth, the P composition is gradually changed from 0.2 to 0 from the start to the end of growth, and the As composition is gradually changed from 0.3 to 0.5 from the start to the end of growth, that is, Al is formed when the growth of the transition layer 203 is ended 0.5 As 0.5 。
In this embodiment, the lattice constant of the material of the transition layer 203 is relatively close to that of the first distributed bragg reflector layer 202 at the beginning, and then gradually changes to be relatively close to that of the second distributed bragg reflector layer 202, so that the mismatch stress between the first distributed bragg reflector layer 202 and the second distributed bragg reflector layer 202 can be released better, and the crystal quality is improved.
After the growth of the transition layer 203, the second distributed bragg mirror layer 204 is grown on the transition layer 203. The second dbr layer 204 is a periodic structure in which second AlAs layers 2041 and AlGaAs layers 2042 are alternately arranged. The periodicity of the second dbr layer 204 is greater than one half of the total periodicity of the dbr layer, and in order to achieve both high reflectivity and low warpage, the periodicity of the second dbr layer 204 is preferably three-quarters of the total periodicity of the dbr layer, that is, the periodicity of the second dbr layer 204 is preferably 24-60.
The second dbr layer 204 is doped with a first dopant, such as an n-type dopant, and may be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Further, the first dopant is preferably Si. The concentration of the first dopant doped in the second DBR layer 204 is preferably 1E18cm -3 ～1E19cm -3 。
The material of the second AlAs layer 2041 includes Al 0.5 As 0.5 But is not limited thereto. The material of the AlGaAs layer 2042 includes (Al) y Ga 1-y ) 0.5 As 0.5 Wherein y is more than or equal to 0.5 and less than or equal to 0.8. The Al composition in the material of the AlGaAs layer 2042 is preferably the same as the Al composition in the AlGaAsP layer 2022, i.e., y ═ x. The optical thickness of each layer of the second DBR layer 204 is 1/4n of the central reflection wavelength, where n is the refractive index of each layer, and n is the wavelength of yellow light AlAs ＝3.2，n AlGaAs 3.9. Further, 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 in each period in the second distributed bragg mirror layer 204. For example, in the reaction chamber of an MOCVD growth furnace, Al is 46nm thick 0.5 As 0.5 And 38nm thick (Al) 0.7 Ga 0.3 ) 0.5 As 0.5 The second distributed bragg mirror layers 204 are alternately arranged in an ABAB manner in 54 periods.
In the prior art, as the lattice constants of AlGaInP of the active layer and GaP of the second type window layer are smaller than those of AlAs and AlGaAs, a larger lattice mismatch causes a larger tensile strain during growth, and the larger the number of periods of the DBR (distributed bragg mirror layer), the larger the strain, the larger the warpage of the epitaxial structure is increased. If AlAs and AlGaAsP are used as the DBR material, the lattice constant can be made small due to the addition of P (phosphorus) to balance the lattice difference between the DBR and the AlGaInP system. However, the reflection effect of the structure of AlAs and AlGaAsP as a mirror is inferior to that of the structure of AlAs and AlGaAs, which is contrary to the original intention of obtaining a yellow LED with high brightness. In the embodiment, a structure composed of AlAs and AlGaAs (i.e., the second dbr layer) and a structure composed of AlAs and AlGaAsP (i.e., the first dbr layer) are used to form the structure of the hybrid dbr layer, that is, the structure composed of AlAs and AlGaAs of a part of cycles is changed to a structure composed of AlAs and AlGaAsP, so as to balance the high warping degree caused by the high-cycle dbr layer and simultaneously consider the high reflectivity required by the dbr layer.
Because there is the difference in lattice constant between first distributed Bragg reflector layer and the second distributed Bragg reflector layer, directly grow second distributed Bragg reflector layer on first distributed Bragg reflector layer and lead to the crystal quality variation of second distributed Bragg reflector layer easily, and this embodiment has designed the transition layer between first distributed Bragg reflector layer and second distributed Bragg reflector layer, the material of transition layer is Al component, Ga component, the structural layer of P component and As component gradual change, can be favorable to the release of mismatch stress, reduce the production of defect, and then can guarantee the growth quality of distributed Bragg reflector layer.
In this embodiment, the second distributed bragg mirror layer 204 is a periodic structure in which second AlAs layers 2041 and AlGaAs layers 2042 are alternately arranged, the first distributed bragg mirror 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 mirror layer 204 is higher than that of the first distributed bragg mirror layer 202, the absorption of light by the second distributed bragg mirror layer is smaller than that of the first distributed bragg mirror layer 202, and the second distributed bragg mirror layer 204 is disposed on a side closer to the active layer 207, so that light emitted by the active layer 207 can be reflected more, the reflectivity of the distributed bragg mirror layer is improved, and the light emitting efficiency of the LED epitaxial structure is improved.
In step S3, after growing the dbr layer, a first type semiconductor layer is grown on the dbr layer. The first-type semiconductor layer sequentially comprises a first-type confinement layer 205 and a first barrier layer 206 from bottom to top.
After growing the dbr layer, a confinement layer of a first type 205 is grown on the dbr layer. The confinement layer of the first type 205 is used to provide electrons. The thickness of the first type confinement layer 205 is preferably 300nm to 800 nm. The first-type confinement layer 205 is preferably made of AlInP, but is not limited thereto. For example, the first-type confinement layer 205 is grown in a thickness of 400nm in the reaction chamber of the MOCVD growth furnace. The first-type confinement layer 205 is doped with a first-type dopant, such as an n-type dopant, and may be at least one of silicon (Si) and tellurium (Te), but is not limited thereto. Further, the first dopant is preferably Si.
After growing the confinement layer of the first type 205, a first barrier layer 206 is grown on the confinement layer of the first type 205. The thickness of the first barrier layer 206 is preferably 50nm to 200 nm. For example, first barrier layer 206 is grown to a thickness of 100nm in the reaction chamber of a MOCVD growth furnace. The first barrier layer 206 is preferably made of AlGaInP, but not limited thereto. The first barrier layer is an undoped structure layer.
After growing the first barrier layer 206, 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 400 nm. The active layer 207 is preferably of a multi-quantum well structure, that is, the active layer 207 is preferably of a periodic structure consisting of quantum wells and quantum barriers, and the period number of the active layer 207 is preferably 30-80. For example, 40 cycles of the active layer 207 are grown in the reaction chamber of the MOCVD growth furnace.
After the active layer 207 is grown, a second type semiconductor layer is grown on the active layer 207. The second type semiconductor layer sequentially comprises 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.
Accordingly, after growing the active layer 207, a second barrier layer 208 is grown on the active layer 207. The second barrier layer 208 is preferably made of AlGaInP, but not limited thereto. The second barrier layer is an undoped structure layer.
The thickness of the second barrier layer 208 is preferably 100nm to 300nm, and the second barrier layer 208 is grown to a thickness of 200nm in a reaction chamber of an MOCVD growth furnace, for example.
After growing the second barrier layer 208, 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. And said confinement layers of the first type 205 and said confinement layers of the second type 209 have two main functions as confinement layers, on the one hand to provide electron-hole pairs to enter the active layer 207 for recombination and light emission; and on the other hand, minority carriers are limited not to overflow the active layer 207, and the recombination luminous efficiency is improved.
The material of the second-type confinement layer 209 is preferably AlInP, but is not limited thereto. The second-type confinement layer 209 is doped with a second dopant, such as a p-type dopant, and may be at least one of magnesium (Mg) and zinc (Zn), but is not limited thereto. Further, the second dopant is preferably Mg.
The thickness of the second type confinement layer 209 is preferably 200nm to 600 nm. For example, the second type confinement layer 209 is grown to a thickness of 400nm in the reaction chamber of the MOCVD growth furnace.
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 spreading, preventing current from being unevenly distributed 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 is not limited thereto. The thickness of the second type window layer 210 is preferably 500nm to 1500 nm. For example, a second type window layer 210 is grown to a thickness of 1000nm in the reaction chamber of the MOCVD growth furnace.
After growing the second type window layer 210, 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 is not limited thereto. The second-type ohmic contact layer 211 may be doped with carbon (C).
The thickness of the second type ohmic contact layer 211 is preferably 100nm to 250 nm. For example, the second type ohmic contact layer 211 is grown in a thickness of 200nm in a reaction chamber of the MOCVD growth furnace.
The first distributed Bragg reflector layer is a periodic structure formed by alternately arranging first AlAs layers and AlGaAsP layers, the second distributed Bragg reflector layer is a periodic structure formed by alternately arranging second AlAs layers and AlGaAs layers, and the first distributed Bragg reflector layer and the second distributed Bragg reflector layer jointly form the distributed Bragg reflector layer, so that high warping degree caused by the high-periodicity distributed Bragg reflector layer can be balanced, and high reflectivity required by the distributed Bragg reflector layer is considered at the same time.
In addition, the transition layer is arranged between the first distributed Bragg reflector layer and the second distributed Bragg reflector layer and is a structural layer with gradually changed Al components, Ga components, P components and As components, so that the stress can be released favorably, the defects can be reduced, and the growth quality of the distributed Bragg reflector layer can be further ensured.
In addition, it is to be understood that while the present invention has been described in conjunction with the preferred embodiments thereof, it is not intended to limit the invention to those embodiments. It will be apparent to those skilled in the art that many changes and modifications can be made, or equivalents employed, to the presently disclosed embodiments without departing from the intended scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.
It is to be further understood that the present invention is not limited to the particular methodology, compounds, materials, manufacturing techniques, uses, and applications described herein, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. It must be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a step" means a reference to one or more steps and may include sub-steps. All conjunctions used should be understood in the broadest sense. Thus, the word "or" should be understood to have the definition of a logical "or" rather than the definition of a logical "exclusive or" unless the context clearly dictates otherwise. Structures described herein are to be understood as also referring to functional equivalents of such structures. Language that can be construed as approximate should be understood as such unless the context clearly dictates otherwise.

Claims (22)

1. The utility model provides a LED epitaxial structure which characterized in that, LED epitaxial structure includes from supreme down in proper order: the distributed Bragg reflector comprises a bottom buffer layer, 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 sequentially comprises a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer from bottom to top; the second distributed Bragg reflector layer is of a periodic structure with second AlAs layers and AlGaAs layers arranged alternately.
2. LED epitaxial structure according to claim 1, characterized in that the material of the first AlAs layer comprises Al 0.5 As 0.5 (ii) a The describedThe material of AlGaAsP layer includes (Al) x Ga 1-x ) 0.5 As 0.3 P 0.2 Wherein x is more than or equal to 0.5 and less than or equal to 0.8; the material of the second AlAs layer comprises Al 0.5 As 0.5 (ii) a The material of the AlGaAs layer comprises (Al) y Ga 1-y ) 0.5 As 0.5 Wherein y is more than or equal to 0.5 and less than or equal to 0.8.
3. The LED epitaxial structure of claim 1, wherein the optical thickness of each of 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 material.
4. The LED epitaxial structure of claim 1, wherein the first dbr layer has a periodicity of less than one half of the total periodicity of the dbr layers and the second dbr layer has a periodicity of greater than one half of the total periodicity of the dbr layers.
5. The LED epitaxial structure of claim 4, wherein the first DBR layer has a periodicity of one quarter of the total periodicity of the DBR layers and the second DBR layer has a periodicity of three quarters of the total periodicity of the DBR layers.
6. An LED epitaxial structure according to claim 2 wherein the material of the transition layer comprises (Al) a Ga 1-a ) 0.5 As 0.5-b P b Wherein a is more than or equal to 0.5 and less than or equal to 1, and b is more than or equal to 0 and less than or equal to 0.2.
7. The LED epitaxial structure of claim 6, wherein the Al composition in the transition layer is graded from x to 1 along the direction the first distributed bragg mirror layer points towards the second distributed bragg mirror layer; the P component in the transition layer is gradually changed from 0.2 to 0 along the direction of the first distributed Bragg reflector layer pointing to the second distributed Bragg reflector layer.
8. The LED epitaxial structure of claim 1, wherein the transition layer has a thickness of 10nm to 50 nm.
9. The LED epitaxial structure of claim 1, wherein the dbr layer is doped with Si at a concentration of 1E18cm -3 ～1E19cm -3 。
10. The LED epitaxial structure of claim 1, wherein the first-type semiconductor layer comprises, in order from bottom to top, a first-type confinement layer and a first barrier layer.
11. The LED epitaxial structure of claim 1, wherein the second type semiconductor layer comprises, in order 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.
12. A preparation method of an LED epitaxial structure is characterized by comprising the following steps:
providing a substrate;
the distributed Bragg reflector comprises a bottom buffer layer and a distributed Bragg reflector layer which sequentially grow on the substrate, wherein the distributed Bragg reflector layer sequentially comprises a first distributed Bragg reflector layer, a transition layer and a second distributed Bragg reflector layer from bottom to top, and the first distributed Bragg reflector layer is a periodic structure formed by alternately arranging a first AlAs layer and an AlGaAsP layer; the second distributed Bragg reflector layer is a periodic structure formed by alternately arranging second AlAs layers and AlGaAs layers;
and growing a first type semiconductor layer, an active layer and a second type semiconductor layer on the distributed Bragg reflector layer in sequence.
13. The method for preparing an LED epitaxial structure according to claim 12, wherein the material of the first AlAs layer comprises Al 0.5 As 0.5 (ii) a The material of the AlGaAsP layer comprises (Al) x Ga 1-x ) 0.5 As 0.3 P 0.2 Wherein x is more than or equal to 0.5 and less than or equal to 0.8; the material of the second AlAs layer comprises Al 0.5 As 0.5 (ii) a The material of the AlGaAs layer comprises (Al) y Ga 1-y ) 0.5 As 0.5 Wherein y is more than or equal to 0.5 and less than or equal to 0.8.
14. The method of fabricating an LED epitaxial structure according to claim 12, wherein the optical thickness of each of the first and second distributed bragg mirror layers is 1/4n of the central reflection wavelength, where n is the refractive index of each layer material.
15. The method according to claim 12, wherein the number of cycles of the first DBR layer is less than one-half of the total number of cycles of the DBR layer, and the number of cycles of the second DBR layer is greater than one-half of the total number of cycles of the DBR layer.
16. The method according to claim 15, wherein the number of cycles of the first DBR layer is one fourth of the total number of cycles of the DBR layer, and the number of cycles of the second DBR layer is three quarters of the total number of cycles of the DBR layer.
17. A method of fabricating an LED epitaxial structure according to claim 13, wherein the material of the transition layer comprises (Al) a Ga 1-a ) 0.5 As 0.5-b P b Wherein a is more than or equal to 0.5 and less than or equal to 1, and b is more than or equal to 0 and less than or equal to 0.2.
18. The method for preparing an LED epitaxial structure according to claim 17, wherein the Al composition in the transition layer is graded from x to 1 along the direction in which the first distributed bragg mirror layer points to the second distributed bragg mirror layer; the P component in the transition layer is gradually changed from 0.2 to 0 along the direction of the first distributed Bragg reflector layer pointing to the second distributed Bragg reflector layer.
19. The method of fabricating an LED epitaxial structure according to claim 12, wherein the thickness of the transition layer is 10nm to 50 nm.
20. The method for preparing an LED epitaxial structure according to claim 12, wherein the dbr layer is doped with Si at a concentration of 1E18cm -3 ～1E19cm -3 。
21. The method for preparing an LED epitaxial structure according to claim 12, wherein the first type semiconductor layer comprises, in order from bottom to top, a first type confinement layer and a first barrier layer.
22. The method of claim 12, wherein the second type semiconductor layer comprises, in order 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.
CN202210556941.8A 2022-05-20 2022-05-20 LED epitaxial structure and preparation method thereof Pending CN115000259A (en)

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