CN112397618A - Epitaxial structure of light emitting diode and preparation method thereof - Google Patents

Epitaxial structure of light emitting diode and preparation method thereof Download PDF

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CN112397618A
CN112397618A CN202011357979.XA CN202011357979A CN112397618A CN 112397618 A CN112397618 A CN 112397618A CN 202011357979 A CN202011357979 A CN 202011357979A CN 112397618 A CN112397618 A CN 112397618A
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algan
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刘园旭
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Anhui University of Traditional Chinese Medicine AHUTCM
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Anhui University of Traditional Chinese Medicine AHUTCM
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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
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
    • H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride 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
    • H01L33/04—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 quantum effect structure or superlattice, e.g. tunnel junction
    • H01L33/06—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 quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
    • 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
    • H01L33/14—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 carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
    • 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
    • H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen

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Abstract

The invention provides a preparation method of an epitaxial structure of a light-emitting diode, which comprises the steps of providing a substrate, and growing a buffer layer, an N-type AlGaN conducting layer and Al on the substrate in sequencexGa1‑xN/AlyGa1‑yN multiple quantum well active layers, wherein x is 0.37-0.38, and y is 0.55-0.6; will grow the Al completelyxGa1‑xN/AlyGa1‑ yAnd chemically etching the epitaxial wafer of the N multi-quantum well active layer, and then continuously carrying out secondary epitaxial growth on the chemically etched epitaxial wafer to obtain the AlGaN electron blocking layer, the P-type AlGaN hole expansion layer and the P-type gallium nitride conducting layer. The LED epitaxial structure prepared by the preparation method has high luminous efficiencyThe improvement is reached.

Description

Epitaxial structure of light emitting diode and preparation method thereof
Technical Field
The invention relates to the technical field of semiconductor device preparation, in particular to an epitaxial structure of a light emitting diode and a preparation method thereof.
Background
Ultraviolet (UV) refers to an electromagnetic wave having a wavelength of 10nm to 400nm, and the shorter the wavelength of the electromagnetic wave, the stronger the radiation, and UV can be classified into UVA (320 to 400nm), UVB (280 to 320nm), and UVC (100 to 280nm) according to the wavelength of the electromagnetic wave. Wherein, the UVC wavelength is between 100 nm and 280nm, can destroy the DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) molecular structure of microorganisms, so that bacteria die or can not be propagated to achieve the aim of sterilization, and therefore, the UVC has wide application in the fields of sterilization, water purification, air purification, medical treatment and the like.
Mercury lamps have been one of the UV sterilization methods, but mercury is highly toxic and unsuitable for long-term development, and a safer and environmentally friendly method is needed to replace mercury lamps. With the continuous development of Light Emitting Diode (LED) technology, the light emitting wavelength of the LED has been expanded from the visible light band to the deep ultraviolet band, and the deep ultraviolet LED has the advantages of low energy consumption, small volume, good integration, long service life, environmental protection, no toxicity and the like as a novel ultraviolet light source, and has a wide application prospect in various fields, but the current deep ultraviolet LED has a low light emitting efficiency and limits the application of the deep ultraviolet LED. Therefore, a preparation method for improving the brightness of the deep ultraviolet LED is urgently needed to be developed.
Disclosure of Invention
Aiming at the defects and shortcomings in the prior art, the invention provides a preparation method of a light-emitting diode epitaxial structure, which is used for solving the problem of low light emitting efficiency of a deep ultraviolet light-emitting diode.
In order to achieve the above and other related objects, the present invention provides a method for preparing an epitaxial structure of a light emitting diode, comprising the steps of:
providing a substrate, and annealing the substrate;
growing a buffer layer on the substrate after the annealing treatment;
growing an N-type AlGaN conducting layer on the buffer layer;
growing Al on the N-type AlGaN conducting layerxGa1-xN/AlyGa1-yN multiple quantum well active layers, wherein x is 0.37-0.38, and y is 0.55-0.66;
will grow the Al completelyxGa1-xN/AlyGa1-yCarrying out chemical corrosion on the epitaxial wafer of the N multi-quantum well active layer;
al after said chemical etchingxGa1-xN/AlyGa1-yContinuously epitaxially growing an AlGaN electron barrier layer on the N multi-quantum well active layer;
growing a P-type AlGaN hole expansion layer on the AlGaN current expansion layer;
and growing a P-type gallium nitride conducting layer on the P-type AlGaN hole expansion layer.
In an embodiment of the invention, growing the buffer layer on the annealed substrate includes:
growing an aluminum nitride buffer layer on the substrate after the annealing treatment;
growing an AlGaN buffer layer on the aluminum nitride buffer layer, wherein the thickness of the AlGaN buffer layer is 300-350 nanometers (nm), and the Al component content of the AlGaN buffer layer is reduced from 80-85% to 60-65% from the beginning to the end of growth.
In an embodiment of the invention, silane is used as a silicon dopant when growing the N-type AlGaN conductive layer on the buffer layer, wherein the silicon doping concentration in the N-type AlGaN conductive layer is 3E18-1E19 cm-3The content of the Al component in the N-type AlGaN conducting layer is 50-55%, and the thickness of the N-type AlGaN conducting layer is 1000-2500 nm.
In an embodiment of the invention, Al is grown on the N-type AlGaN conductive layerxGa1-xN/AlyGa1-yThe N multi-quantum well active layer is Al alternately grownxGa1-xN quantum well layer and AlyGa1-yN quantum barrier layer of AlxGa1-xThe thickness of the N quantum well layer is 2-3 nm, and Al isyGa1-yThe thickness of the N quantum barrier layer is 4-10 nm, and the growth period of the multiple quantum well is 3-10.
Further, growing the AlyGa1-yIntroducing silane as a dopant in the process of the N quantum barrier layer, wherein the Al isyGa1-yThe doping concentration of silicon in the N quantum barrier layer is 5E 17-6E 17cm-3。
In an embodiment of the invention, Al is grown on the N-type AlGaN conductive layerxGa1-xN/AlyGa1-yContinuing to grow an AlGaN protective layer after the N multi-quantum well active layer is finished, wherein the thickness of the AlGaN protective layer is 10-30 nm, and the growth process of the AlGaN protective layer and the AlyGa1-yThe growth conditions of the N quantum barrier layers are the same.
In one embodiment of the present invention, the Al is grown completelyxGa1-xN/AlyGa1-yThe etching solution used for chemical etching of the epitaxial wafer of the N multi-quantum well active layer is a mixed solution of sodium hydroxide and hydrogen peroxide, wherein the ratio of the sodium hydroxide to the hydrogen peroxide is 1 (1-1.5), and the concentration of the mixed solution is 30-35%; the corrosion time of the chemical corrosion is 6-20 minutes.
In an embodiment of the present invention, the Al content of the AlGaN electron blocking layer is reduced from 75-80% to 55-60% from the beginning to the end of growth, and the thickness of the AlGaN electron blocking layer is 20-30 nm.
In an embodiment of the invention, magnesium is used as a magnesium dopant when a P-type AlGaN hole expansion layer is grown on the AlGaN electron blocking layer, wherein the doping concentration of magnesium in the P-type AlGaN hole expansion layer is 1E 19-5E 19cm-3The content of Al components in the P-type AlGaN hole expansion layer is 60-65%, and the thickness of the P-type AlGaN hole expansion layer is 30-50 nm.
In an embodiment of the present invention, the growing the P-type gan conductive layer on the P-type AlGaN hole expansion layer includes:
controlling the growth temperature to be 960-1000 ℃ and the growth pressure to be 200 mbar;
introducing trimethyl gallium and ammonia gas to provide a gallium source and a nitrogen source, and introducing magnesium diclocide as a magnesium dopant, wherein the flow rate of trimethyl gallium is 150-200 sccm, the flow rate of ammonia gas is 20000-22000 sccm, and the flow rate of magnesium diclocide is 600-800 sccm;
the thickness of the P-type gallium nitride conducting layer is 100-300 nm, and the doping concentration of magnesium is 5E19-1E20 cm-3。
The invention also provides a light-emitting diode epitaxial structure prepared based on the preparation method.
As mentioned above, the invention provides a preparation method of a light-emitting diode epitaxial structure, which realizes the coverage of the LED light-emitting wavelength in 200-280 nm by adjusting the Al component in AlGaN and changing the forbidden bandwidth of the AlGaN material, wherein the Al component is in the preparation processxGa1-xN/AlyGa1-yContinuously growing an AlGaN protective layer on the N multi-quantum well active layer, and then corroding the surface of an epitaxial wafer on which the AlGaN protective layer is grown in a chemical corrosion mode, wherein the AlGaN protective layer on the surface of the active layer is quickly corroded inwards along the epitaxial layer with numerous screw dislocation outcrops due to corrosion thinning, a V-shaped opening is formed at the position along the dislocation line after corrosion, and the depth and the size of the opening are controlled by controlling corrosion time; and continuously growing an electron blocking layer AlGaN, a hole expansion layer P-type AlGaN and a P-type GaN hole conducting layer on the surface of the etched epitaxial wafer, and filling the V-shaped opening formed by etching by utilizing the characteristics of lower growth temperature and high growth speed of the P-type GaN layer to finally grow the epitaxial wafer with a smooth surface. The holes generated by the P-type GaN layer can enter the active layer from the longitudinal direction and be recombined with electrons, and the holes can enter more active layers from the side by utilizing the V-shaped opening generated by corrosion to be recombined with electrons to emit light, so that the recombination rate of the electron holes is improved, and the luminous efficiency of the deep ultraviolet LED is improved.
Drawings
The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:
fig. 1 is a flow chart of a method for manufacturing an LED epitaxial structure according to the present invention.
Fig. 2 is a flow chart illustrating a method for fabricating a buffer layer according to an embodiment of the invention.
Fig. 3 is a schematic structural diagram of an AlN buffer layer in an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of an epitaxial wafer after a multiple quantum well active layer is grown.
Fig. 5 is a schematic structural diagram of the epitaxial wafer in fig. 4 after chemical etching.
Fig. 6 is an SEM image of fig. 5.
Fig. 7 is a schematic view of an epitaxial structure of an LED fabricated by the fabrication method of the present invention.
Fig. 8 shows a hole diffusion schematic of a prior art epitaxial structure without chemical etching.
Fig. 9 shows a hole diffusion diagram of an epitaxial structure of an LED prepared according to the present invention.
Fig. 10 is a graph showing the test of the light emission luminance of the chip prepared with the epitaxial structure of the present invention and the chip prepared with the conventional epitaxial structure by the uv-vis integrating sphere tester.
Reference numerals
1 patterned sapphire substrate
2 AlN buffer layer
21 first AlN layer
22 second AlN layer
23 third AlN layer
3 AlGaN buffer layer
4N type AlGaN conductive layer
5 AlxGa1-xN/AlyGa1-yN multiple quantum well active layer
6 AlGaN electron blocking layer
7P type AlGaN hole expansion layer
8P type GaN conducting layer
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict. It is also to be understood that the terminology used in the examples is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. Test methods in which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under conditions recommended by the respective manufacturers.
When numerical ranges are given in the examples, it is understood that both endpoints of each of the numerical ranges and any value therebetween can be selected unless the invention otherwise indicated. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and the description of the present invention, and any methods, apparatuses, and materials similar or equivalent to those described in the examples of the present invention may be used to practice the present invention.
The invention provides a preparation method of an LED epitaxial structure, in AlxGa1-xN/AlyGa1-yAfter the growth of the N multi-quantum well active layer is finished, the N multi-quantum well active layer is quickly corroded towards the inside of the epitaxial layer along a plurality of screw dislocation dislocations through chemical corrosion to form a V-shaped opening, after the P-type GaN is filled, holes can enter the active layer from the longitudinal direction and are compounded with electrons, and the holes can enter more active layers from the side to be compounded with the electrons to emit light by utilizing the V-shaped corrosion pits, so that the recombination rate of the electron holes is improved, and the light emitting efficiency of the deep ultraviolet LED is improved.
The invention provides a preparation method of an LED epitaxial structure, which can be carried out in Metal Organic Chemical Vapor Deposition (MOCVD) equipment by using trimethylaluminum (TMAl), trimethylgallium (TMGa) and ammonia (NH)3) Hydrogen (H) as aluminum (Al) source, gallium (Ga) source and nitrogen (N) source2) Nitrogen (N)2) Or the mixture of the two is used as carrier gas.
Referring to fig. 1 to 6, the present invention provides a method for manufacturing an LED epitaxial structure, including the following steps:
s1, providing a substrate, and annealing the substrate;
s2, growing a buffer layer on the substrate;
s3, growing an N-type AlGaN conducting layer 4 on the buffer layer;
s4, growing Al on the N-type AlGaN conducting layerxGa1-xN/AlyGa1-yN multiple quantum well active layer 5, wherein x is 0.37-0.38, y is 0.55-0.60;
S5、will grow the Al completelyxGa1-xN/AlyGa1-yChemically etching the epitaxial wafer of the N multi-quantum well active layer 5;
s6, continuously epitaxially growing an AlGaN electron barrier layer 6 on the epitaxial wafer after the chemical corrosion;
s7, growing a P-type AlGaN hole expansion layer 7 on the AlGaN electron blocking layer 6;
and S8, growing a P-type GaN conducting layer 8 on the P-type AlGaN hole expanding layer 7.
Referring to fig. 1 and 4, the substrate in step S1 may be selected as the patterned sapphire substrate 1, the annealing process is performed in a hydrogen atmosphere at 1000 ℃, 100mbar, 3-5 min, and the annealing process is performed on the substrate to remove the smut and oxide layer on the surface of the substrate.
Referring to fig. 1 to 4, the step S2 of growing the buffer layer on the annealed substrate includes:
s21, growing an AlN buffer layer 2 on the substrate; and
s22, an AlGaN buffer layer 3 is grown on the AlN buffer layer 2.
Wherein, in the step S21, TMAl and NH are introduced into the reaction chamber to grow the AlN buffer layer 2 on the substrate3To provide an Al source and an N source while feeding H2As a carrier gas. In one embodiment, growing the AlN buffer layer 2 includes the steps of: growing a first AlN layer 21 on the substrate, wherein the temperature of the reaction chamber in the growth stage is controlled to be 900-950 ℃, the pressure is controlled to be 50-100 mbar, the flow rate of TMAl is 200-250 sccm, the molar ratio of V/III element is 3000-4000, and the thickness of the first AlN layer 21 grown in the growth stage is 20-40 nm; then growing a second AlN layer 22 on the first AlN layer 21, wherein the temperature of the reaction chamber in the growth stage is 1100-1150 ℃, the pressure of the reaction chamber is kept unchanged, the flow rate of TMAl is 180-220 sccm, the molar ratio of V/III is 4000-5000, and the thickness of the second AlN layer 22 grown in the growth stage is 300-500 nm; then, a third AlN layer 23 is grown on the second AlN layer 22, the temperature of the reaction chamber is increased to 1220-1300 ℃, the pressure of the reaction chamber is kept unchanged, the flow rate of the TMAl is 380-450 sccm, and V & ltSUB & gt & lt/SUB & gtIII is 100 to 300, and the thickness of the third AlN layer 33 grown at this growth stage is 1.5 to 3.5 μm. The first AlN layer 21 grows rapidly at a low temperature, and compared with a subsequent high-temperature growth layer with a relatively low-temperature A1N doped layer, dislocation blocking and substrate stress relief are facilitated; the second AlN layer 22 grows at a medium temperature, and gradually transits from a low temperature to a high temperature to be equivalent to a transition layer, so that the growth of the A1N buffer layer 2 is transited from three-dimension to two-dimension, the surface is roughened to be changed into flatness, the dislocation is cut off and penetrates upwards, the dislocation density of a subsequent upward epitaxial layer is reduced, and the gradual release and relief of stress are facilitated; the third AlN layer 23 is grown at high temperature, the surface migration capability of A1 atoms is strong at high temperature, two-dimensional growth is realized, and an A1N epitaxial layer material with low dislocation density, no crack and smooth surface can be obtained. The AlN buffer layer 2 grown in a segmented mode can block upward epitaxial dislocation better, is beneficial to gradual release of stress and is more beneficial to epitaxial growth of a high-quality epitaxial layer.
Step S22, growing AlGaN buffer layer 3 on AlN buffer layer 2, introducing TMGa, TMAl, NH into the reaction chamber3Providing Ga source, Al source and N source, and introducing H2As a carrier gas. The temperature of the reaction chamber in the growth stage is 1060-1100 ℃, the pressure is 50-100 mbar, the flow rate of TMGa is 50-60 sccm, NH3The flow rate of the TMAl is 8000-9000 sccm, and the flow rate of the TMAl is reduced from the start of growth to the end of growth from 250-270 sccm to 130-150 sccm. In this stage, the Al content of the AlGaN buffer layer 3 is reduced from 80-85% to 60-65% from the beginning to the end, and the thickness of the AlGaN buffer layer 3 is 300-350 nm. The Al component content in the AlGaN buffer layer 3 gradually changes from high to low, the surface in contact with the AlN buffer layer 2 is the AlGaN buffer layer 3 with high Al component, and the surface in contact with the N-type AlGaN conducting layer 4 is low Al component, so that the lattice constant of the buffer layer gradually approaches to the N-type AlGaN conducting layer 4, the difference between layers is reduced, and the crystal quality of the epitaxial layer is improved.
Referring to fig. 1 and 4, in step S3, an N-type AlGaN conductive layer 4 is grown on the buffer layer to provide electrons for the LED epitaxial structure, and TMGa, TMAl, and NH are introduced into the reaction chamber during the growth of the N-type AlGaN conductive layer3Providing Ga source, Al source and N sourceWhile introducing Silane (SiH)4) As Si dopant, H is introduced2As a carrier gas. The temperature in the reaction chamber in the growth stage is 1080-1100 ℃, the pressure is 50-100 mbar, the flow rate of TMGa is 50-60 sccm, the flow rate of TMAl is 120-140 sccm, and NH is added3The flow rate of the Al-doped N-type AlGaN conductive layer 4 is 2000-2500 sccm, the Al component content of the Si-doped N-type AlGaN conductive layer 4 grown at the stage is 50-55%, and the doping concentration of Si is 3E18-1E19 cm-3The thickness of the N-type AlGaN conducting layer is 1000-2500 nm.
Referring to fig. 1 and 4, in step S4, Al is grown on the N-type AlGaN conductive layer 4xGa1-xN/AlyGa1-yThe N multi-quantum well active layer 5 is Al grown alternatelyxGa1-xN quantum well layer and AlyGa1-yN quantum barrier layer of AlxGa1-xX in N is 0.37-0.38, AlyGa1-yY in N is 0.55-0.6, each layer of AlxGa1-xThe thickness of the N quantum well is 2-3 nm, and each layer of AlyGa1-yThe thickness of the N quantum barrier is 4-10 nm, and AlxGa1-xN quantum well layer and AlyGa1-yThe period of the alternate growth of the N quantum barrier layers is 3-10. Introducing TMGa, TMAl and NH into the reaction chamber in the growth stage3Providing Ga source, Al source and N source, and introducing H2And N2As a carrier gas, wherein H2And N2The flow ratio of (2) is 4: 1. The temperature of the reaction chamber in the growth stage is 1080-1100 ℃, the pressure is 50-100 mbar, and Al growsxGa1-xWhen the N quantum well layer is adopted, the TMGa flow is 20-24 sccm, and the TMAl flow is 22-25 sccm; growing AlyGa1-yGrowing Al with TMGa flow of 20-24 sccm and TMAl flow of 60-65 sccm in the case of N quantum barrier layeryGa1-ySiH is also required to be introduced when the N quantum barrier layer is formed4As Si dopant, AlyGa1-yThe doping concentration of Si in the N quantum barrier layer is 5E 17-6E 17cm-3。
In one embodiment, the last layer of Al is grownyGa1-yAfter N quantum barrier, continuously growing an AlGaN protective layer with the thickness of 10-30 nm under the same growth condition to ensure thatAnd protecting the active layer from being excessively corroded in the subsequent corrosion process. And after the growth is finished, cooling, and taking out the epitaxial wafer after the first growth from the reaction chamber.
Referring to FIGS. 1, 4 and 5, step S5, the Al is grown completelyxGa1-xN/AlyGa1-yAnd after the temperature of the epitaxial wafer of the N multi-quantum well active layer is reduced to room temperature, taking out the epitaxial wafer from the reaction chamber and putting the epitaxial wafer into corrosive liquid for chemical corrosion. Wherein the corrosive liquid is sodium hydroxide (NaOH) and hydrogen peroxide (H)2O2) Mixed solution of (3), NaOH and H2O2In a ratio of 1: (1-1.5), wherein the concentration of the mixed solution is 30-35%. When chemical corrosion is carried out, the temperature of the corrosive liquid needs to be controlled at 50 ℃ through a temperature control device, the corrosion time is 5-20 minutes (min), and the corrosion time and the active layer Al are controlledxGa1-xN/AlyGa1-yThe growth period of N is related, the more quantum well layers are grown, the longer the etching time is for etching to the bottom of the active layer, for example, when AlxGa1-xN/AlyGa1-yWhen the growth period of N is 3, the corrosion time is 5-6 min; when Al is presentxGa1-xN/AlyGa1-yWhen the growth period of N is 10, the etching time is 18-20 min. After the etching is finished, taking out the epitaxial wafer, cleaning the epitaxial wafer by using deionized water, and then using N2And (5) drying.
The AlGaN layer has higher defect density, wherein the edge dislocation density is 5E 18-1E19 cm-2In the range, when carrying out chemical etching, not only the AlGaN on epitaxial layer surface thins because of corroding, still can corrode to epitaxial layer inside fast along the dislocation of surperficial outcrop simultaneously, can form the opening of back taper (V-arrangement) on the position along the dislocation line after corroding, can control the degree of depth and the size of opening through the time of control corruption. After the etched epitaxial wafer is sampled, the sample is observed under a Scanning Electron Microscope (SEM), and referring to fig. 6, it can be seen that a large number of etch pits are formed on the surface of the epitaxial wafer.
Referring to fig. 1, 5 and 7, in step S6, after the etching is finished, the epitaxial wafer is placed in the reaction chamber to continue the secondary epitaxial growth, and firstly, the etched epitaxial wafer continues to grow onEpitaxially growing AlGaN electron blocking layer 6, and introducing NH at the temperature raising stage3The epitaxial layer is protected from decomposition. The growth temperature of the AlGaN electron blocking layer 6 is 1050-1080 ℃, the pressure is 50-100 mbar, the flow of TMGa is 50-60 sccm, and NH is added3The flow rate of the AlGaN electron blocking layer is 2000-3000sccm, the flow rate of TMAl is gradually changed from 230-260 sccm to 130-150sccm from the beginning to the end of growth, the content of Al component in the AlGaN electron blocking layer 6 is reduced from 75-80% to 55-60% from the beginning to the end of growth, and the thickness of the layer is 20-30 nm.
Referring to fig. 1 and 7, in step S7, a P-type AlGaN hole expansion layer 7, TMGa, TMAl, NH, is grown on the AlGaN electron blocking layer 63Providing Ga source, Al source and N source, introducing magnesium metallocene (Cp2Mg) as Mg dopant, and introducing H2As a carrier gas. The temperature of the reaction chamber in the growth stage is 1050-1080 ℃, the pressure is 50-100 mbar, the flow rate of TMGa is 60-65 slm, and the flow rate of TMAl is 150-200 slm. The content of Al component in the P-type AlGaN hole expanding layer 7 is 60-65%, the thickness of the layer is 30-50 nm, and the doping concentration of Mg is 1E 19-5E 19cm-3. The P-type AlGaN hole expansion layer 7 can improve the uniformity of P-pole hole injection, thereby improving the internal quantum efficiency.
Referring to fig. 1 and 7, in step S8, a P-type GaN conductive layer 8 is grown on the P-type AlGaN hole expansion layer 7 to provide holes for the LED epitaxial structure. In the growth stage, TMGa and NH are required to be introduced into the reaction chamber3Providing Ga source and N source, simultaneously introducing Cp2Mg serving as dopant, and introducing H2As a carrier gas. The growth temperature of the stage is 960-1000 ℃, the growth pressure is 200mbar, the flow of TMGa is 150-200 sccm, and NH is added3The flow rate of the catalyst is 20000 to 22000sccm, and the flow rate of Cp2Mg is 600 to 800 sccm. The doping concentration of Mg in the P-type GaN conductive layer 8 is 5E19-1E20 cm-3The thickness of the P-type GaN conductive layer 8 is 100-300 nm. The growth stage is carried out at a lower temperature, and the V-shaped pits formed on the surface of the active layer can be filled, so that the P-type GaN conducting layer 8 can grow and be connected with the surface of the V-shaped pits into a whole.
Referring to fig. 7, the present invention further provides an LED epitaxial structure prepared by the above preparation method, including:
a substrate;
a buffer layer on the substrate;
the N-type AlGaN conducting layer 4 is positioned on the buffer layer;
AlxGa1-xN/AlyGa1-yan N multi-quantum well active layer 5, wherein x is 0.37-0.38, y is 0.55-0.6, and the N multi-quantum well active layer is positioned on the N type AlGaN conducting layer 4;
AlGaN electron blocking layer 6 at AlxGa1-xN/AlyGa1-yN multiple quantum well active layer 5;
the P-type AlGaN hole expansion layer 7 is positioned on the AlGaN electron blocking layer 6;
the P-type GaN conducting layer 8 is positioned on the P-type AlGaN hole expanding layer 7;
wherein, AlxGa1-xN/AlyGa1-yThe N multiple quantum well active layer 5 is provided with a V-shaped opening formed by etching.
Referring to fig. 7, in one embodiment, the substrate is a patterned sapphire substrate 1;
referring to fig. 3 and 7, in an embodiment, the buffer layer comprises an AlN buffer layer 2 on the patterned sapphire substrate 1 and an AlGaN buffer layer 3 on the AlN buffer layer 2, wherein the AlN buffer layer 2 comprises a first AlN layer 21, a second AlN layer 22 on the first AlN layer 21, and a third AlN layer 23 on the second AlN layer 22, the first AlN layer 21 has a thickness of 20 to 40nm, the second AlN layer 22 has a thickness of 400 to 600nm, and the third AlN layer 23 has a thickness of 1.5 to 3.5 μm; the Al component in the AlGaN buffer layer 3 is reduced to 60-65% from 80-85% from bottom to top, and the thickness of the AlGaN buffer layer 3 is 300-350 nm.
Referring to FIG. 7, in an embodiment, the content of Al component in the N-type AlGaN conductive layer 4 is 50-55%, and the doping concentration of Si is 3E18-1E19 cm-3The thickness of the N-type AlGaN conducting layer is 1000-2500 nm.
Referring to FIG. 7, in one embodiment, AlxGa1-xN/AlyGa1-yThe N multi-quantum well active layer 5 is made of AlxGa1-xN quantum well layer and AlyGa1-yN quantum barrier layers alternately grown, each AlxGa1-xThe thickness of the N quantum well layer is 2-3 nm, and each Al layeryGa1-yThe thickness of the N quantum barrier layer is 4-10 nm, the growth period of the N quantum barrier layer and the growth period of the N quantum barrier layer are 3-10 nm, wherein AlyGa1-yThe N quantum barrier layer is Si-doped AlyGa1-yThe doping concentration of N and Si is 5E 17-6E 17cm-3。
Referring to FIG. 7, in one embodiment, AlxGa1-xN/AlyGa1-yA Si-doped AlGaN protective layer with the thickness of 10-30 nm is further formed on the N multi-quantum well active layer 5, the content of Al in the AlGaN protective layer is 55-60%, and the Si doping concentration in the AlGaN protective layer is 5E 17-6E 17cm-3。
Referring to fig. 7, in an embodiment, the content of the Al component in the AlGaN electron blocking layer 6 gradually changes from 75 to 80% to 55 to 60% from bottom to top, and the thickness of the AlGaN electron blocking layer 6 is 20 to 30 nm.
Referring to FIG. 7, in one embodiment, the content of Al component in the P-type AlGaN hole-expanding layer 7 is 60-65%, and the Mg doping concentration is 1E 19-5E 19cm-3The thickness of the P-type AlGaN hole expansion layer 7 is 30-50 nm.
Referring to FIG. 7, in one embodiment, the doping concentration of Mg in the P-type GaN conductive layer 8 is 5E19-1E20 cm-3The thickness of the P-type GaN conductive layer 8 is 100-300 nm.
Referring to fig. 8 and 9, in the conventional LED epitaxial structure, holes in the P-type conductive layer longitudinally migrate along the direction of the active layer, and since the holes migrate slowly, only a small amount of holes migrate into the multiple quantum well active layers, and the number of electrons in the quantum well active layers is much larger than that of the holes, the recombination rate of the electron holes is low, resulting in low light emission rate of the LED; the LED epitaxial structure prepared by the preparation method of the invention is characterized in that Al is adoptedxGa1-xN/AlyGa1-yThe N multi-quantum well active layer 5 is chemically etched to form a large number of V-shaped openings, holes in the P-type GaN conducting layer 8 can be compounded with electrons from the active layer in the longitudinal direction, and more Al can enter from the side face of the active layer by utilizing the V-shaped etch pitsxGa1-xN/AlyGa1-yIn the N multiple quantum well active layer 5 and in the active layerThe electron recombination increases the recombination rate of electron holes and greatly improves the luminous efficiency of the LED.
Referring to fig. 10, the same LED epitaxial structure prepared by the conventional method is used for comparison, the LED epitaxial structure prepared by the conventional method is prepared into a chip a, the LED epitaxial structure prepared by the present invention is prepared into a chip B, the ultraviolet-visible integrating sphere tester is used to test the luminance of the chip a and the chip B, it is shown that the luminance of the chip B prepared by the LED epitaxial structure of the present invention is greater than that of the chip a prepared by the conventional epitaxial structure, and the luminance difference is larger and larger as the current increases.
In summary, the invention discloses a method for preparing an LED epitaxial structure, which includes performing secondary epitaxial growth, performing chemical etching on an epitaxial wafer after the first epitaxial growth of an active layer is completed to form an etch defect on the surface of the epitaxial wafer, and performing secondary epitaxial growth after the etching is completed to form a complete epitaxial structure. The preparation method provided by the invention increases the diffusion space of the holes, so that more holes enter the active layer to be compounded with electrons, the recombination rate of the electron holes is further improved, and the luminous efficiency of the LED is improved. Therefore, the invention effectively overcomes some practical problems in the prior art, thereby having high utilization value and use significance.
The foregoing embodiments are merely illustrative of the principles of this invention and its efficacy, rather than limiting it, and various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the invention, which is defined in the appended claims.

Claims (10)

1. A preparation method of a light emitting diode epitaxial structure is characterized by comprising the following steps:
providing a substrate, and annealing the substrate;
growing a buffer layer on the substrate after the annealing treatment;
growing an N-type AlGaN conducting layer on the buffer layer;
growing Al on the N-type AlGaN conducting layerxGa1-xN/AlyGa1-yN multiple quantum well active layers, wherein x is 0.37-0.38, and y is 0.55-0.60;
will grow the Al completelyxGa1-xN/AlyGa1-yCarrying out chemical corrosion on the epitaxial wafer of the N multi-quantum well active layer;
al after said chemical etchingxGa1-xN/AlyGa1-yContinuously epitaxially growing an AlGaN electron barrier layer on the N multi-quantum well active layer;
growing a P-type AlGaN hole expansion layer on the AlGaN electron blocking layer;
and growing a P-type gallium nitride conducting layer on the P-type AlGaN hole expansion layer.
2. The method of claim 1, wherein growing a buffer layer on the annealed substrate comprises:
growing an aluminum nitride buffer layer on the substrate after the annealing treatment;
growing an AlGaN buffer layer on the aluminum nitride buffer layer, wherein the thickness of the AlGaN buffer layer is 300-350 nanometers, and the Al component content of the AlGaN buffer layer is reduced from 80-85% to 60-65% from the beginning to the end of growth.
3. The method according to claim 1, wherein silane is used as a silicon dopant when growing the N-type AlGaN conductive layer on the buffer layer, wherein the doping concentration of silicon in the N-type AlGaN conductive layer is 3E18-1E19 cm-3The content of Al in the N-type AlGaN conducting layer is 50-55%, and the thickness of the N-type AlGaN conducting layer is 1000-2500 nm.
4. The method according to claim 1, wherein Al is grown on the N-type AlGaN conductive layerxGa1- xN/AlyGa1-yThe N multi-quantum well active layer is Al alternately grownxGa1-xN quantum well layer and AlyGa1-yN quantum barrier layers, wherein,AlxGa1-xthe thickness of the N quantum well layer is 2-3 nanometers, and Al isyGa1-yThe thickness of the N quantum barrier layer is 4-10 nanometers, and the growth cycle of the multiple quantum well is 3-10; growing the AlyGa1-yIntroducing silane as a dopant in the process of the N quantum barrier layer, wherein the Al isyGa1-yThe doping concentration of silicon in the N quantum barrier layer is 5E 17-6E 17cm-3。
5. The method according to claim 4, wherein Al is grown on the N-type AlGaN conductive layerxGa1- xN/AlyGa1-yContinuing to grow an AlGaN protective layer after the N multi-quantum well active layer is finished, wherein the thickness of the AlGaN protective layer is 10-30 nanometers, and the growth process of the AlGaN protective layer and the AlyGa1-yThe growth conditions of the N quantum barrier layers are the same.
6. The method according to claim 1, wherein the Al is grown completelyxGa1-xN/AlyGa1-yThe etching solution used for chemical etching of the epitaxial wafer of the N multi-quantum well active layer is a mixed solution of sodium hydroxide and hydrogen peroxide, wherein the ratio of the sodium hydroxide to the hydrogen peroxide is 1 (1-1.5), and the concentration of the mixed solution is 30-35%; the corrosion time of the chemical corrosion is 6-20 minutes.
7. The method according to claim 1, wherein the Al content of the AlGaN electron blocking layer is reduced from 75 to 80% to 55 to 60% from the start of growth to the end of growth, and the thickness of the AlGaN electron blocking layer is 20 to 30 nm.
8. The preparation method according to claim 1, wherein magnesium is used as a magnesium dopant when growing the P-type AlGaN hole expansion layer on the AlGaN electron blocking layer, and the doping concentration of magnesium in the P-type AlGaN hole expansion layer is 1E 19-5E 19cm-3In the P-type AlGaN hole-expanding layerThe Al component content is 60-65%, and the thickness of the P-type AlGaN hole expansion layer is 30-50 nm.
9. The method of claim 1, wherein growing a P-type gallium nitride conductive layer on the P-type AlGaN hole expanding layer comprises: controlling the growth temperature to be 960-1000 ℃ and the growth pressure to be 200 mbar;
introducing trimethyl gallium and ammonia gas to provide a gallium source and a nitrogen source, and introducing magnesium diclocide as a magnesium dopant, wherein the flow rate of trimethyl gallium is 150-200 sccm, the flow rate of ammonia gas is 20000-22000 sccm, and the flow rate of magnesium diclocide is 600-800 sccm;
the doping concentration of magnesium in the P-type gallium nitride conducting layer is 5E19-1E20 cm-3The thickness of the P-type gallium nitride conducting layer is 100-300 nanometers.
10. An epitaxial structure of a light emitting diode prepared according to the preparation method of any one of claims 1 to 9.
CN202011357979.XA 2020-11-27 2020-11-27 Epitaxial structure of light emitting diode and preparation method thereof Pending CN112397618A (en)

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