CN120813136B - LED epitaxial structure and preparation method thereof - Google Patents
LED epitaxial structure and preparation method thereofInfo
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- CN120813136B CN120813136B CN202511292427.8A CN202511292427A CN120813136B CN 120813136 B CN120813136 B CN 120813136B CN 202511292427 A CN202511292427 A CN 202511292427A CN 120813136 B CN120813136 B CN 120813136B
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- H—ELECTRICITY
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- H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
- H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
- H10H20/80—Constructional details
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- H10H20/811—Bodies having quantum effect structures or superlattices, e.g. tunnel junctions
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- H10H20/01—Manufacture or treatment
- H10H20/011—Manufacture or treatment of bodies, e.g. forming semiconductor layers
- H10H20/013—Manufacture or treatment of bodies, e.g. forming semiconductor layers having light-emitting regions comprising only Group III-V materials
- H10H20/0133—Manufacture or treatment of bodies, e.g. forming semiconductor layers having light-emitting regions comprising only Group III-V materials with a substrate not being Group III-V materials
- H10H20/01335—Manufacture or treatment of bodies, e.g. forming semiconductor layers having light-emitting regions comprising only Group III-V materials with a substrate not being Group III-V materials the light-emitting regions comprising nitride materials
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- H10H20/813—Bodies having a plurality of light-emitting regions, e.g. multi-junction LEDs or light-emitting devices having photoluminescent regions within the bodies
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- H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
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- H10H20/822—Materials of the light-emitting regions
- H10H20/824—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP
- H10H20/825—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP containing nitrogen, e.g. GaN
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Abstract
本发明提供一种LED外延结构及其制备方法，采用MOCVD方法沉积生长外延结构，外延结构包括衬底，以及在衬底上以第一方向依次设置的N型半导体层、量子点有源层、P型半导体层；其中，所述量子点有源层包括沿第一方向依次设置的InN蓝光量子点有源层、InN绿光量子点有源层、InN红光量子点有源层，本申请设置多层InN量子点有源层来实现多波长发光，且有效抑制传统结构带来的密度缺陷，并通过不同的量子点尺寸、量子点阱层厚度、Al组分设置来调节光谱，使LED器件发光均匀。
This invention provides an LED epitaxial structure and its fabrication method. The epitaxial structure is deposited and grown using MOCVD. The epitaxial structure includes a substrate and an N-type semiconductor layer, a quantum dot active layer, and a P-type semiconductor layer sequentially disposed on the substrate in a first direction. The quantum dot active layer includes an InN blue quantum dot active layer, an InN green quantum dot active layer, and an InN red quantum dot active layer sequentially disposed along the first direction. This application uses multiple InN quantum dot active layers to achieve multi-wavelength light emission and effectively suppresses the density defects caused by traditional structures. The spectrum can be adjusted by different quantum dot sizes, quantum dot well layer thicknesses, and Al composition settings to make the LED device emit light uniformly.
Description
Technical Field
The invention belongs to the technical field of semiconductor photoelectrons, and particularly relates to an LED epitaxial structure and a preparation method thereof.
Background
In recent years, the LED device is widely used in the fields of illumination, display, medical treatment, visible light communication and the like by virtue of the advantages of small size, high efficiency, energy saving, long service life and the like. Along with the progress of technology and the improvement of living standard of people, the requirements of people on illumination are not high-brightness and high-light-efficiency illumination modes, but more energy-saving, environment-friendly, healthy and intelligent artificial illumination modes are pursued. The full spectrum fluorescent powder-free illumination is one of the development trends of the LED illumination technology, and can improve the spectrum quality of the LED illumination and improve the life of human beings. The current mode of realizing multiple wavelengths is mainly realized by a multi-chip multi-primary LED.
In the traditional LED structure, the active area is the superposition of the InCaN trap layer and the CaN barrier layer, the longer the light-emitting wavelength is, the higher the required In component is, the lower the light-emitting efficiency is, the wavelengths of blue light, green light and red light are sequentially increased, and the required In component is sequentially increased, so that the light-emitting efficiency is sequentially reduced. Thus, there is a need to increase the luminous efficiency of red light, but In existing GaN-based LED systems, achieving efficient red light emission faces a number of technical challenges, the core difficulty being the contradiction between the intrinsic properties of In xGa1-x N materials (x > 0.4) with high In composition and the growth/device design, including In particular the following aspects:
1. The red light emission requires an In component x >0.4 (corresponding to a forbidden band width <2.0 eV), but the material growth of the high In component is difficult, particularly, the fact that the lattice mismatch between InCaN of the high In component and a GaN substrate is serious, the dislocation is increased, the luminous efficiency is obviously reduced, in atoms tend to be accumulated In InGaN clusters, the uniformity of the material is destroyed, the emission peak is widened and the wavelength drifts are caused, the vapor pressure of In is far higher than that of Ga, the growth of the high In component needs to strictly control the supply rate of a group III source (TMIn), if the supply is insufficient, a 'vacancy cluster' where In atoms are lost is easily formed, and if the supply is excessive, the In atoms cannot be uniformly doped into the lattice due to the weak migration capability of the In atoms (the surface diffusion length is only about 0.1 nm), the In segregation (the local In content is > 0.5) or the three-dimensional island growth is formed (rather than the ideal two-dimensional lamellar growth), and the crystallization quality is further deteriorated.
2. Even if the growth difficulty is overcome to obtain high-quality high-In component InGaN, the intrinsic physical characteristics of the InGaN still can obviously limit the performance of the red LED, namely, the carrier separation is caused by the strong polarization effect of a GaN system, the radiation recombination rate is directly reduced by the carrier separation, the electron mobility and the hole mobility of the high-In component InGaN are both obviously lower than those of GaN, the carrier (especially the hole) is difficult to effectively inject into a quantum well due to the low mobility, and the carrier is easy to be captured by defects after the injection, so that the radiation recombination efficiency is further reduced. In addition, carrier transport irregularities between quantum wells (too high carrier concentration In the well region of high In composition) may cause auger recombination, exacerbating light emission efficiency degradation.
Therefore, the traditional well barrier superposition structure has large stress and is easy to lattice mismatch, and the distribution of carriers and density defects can be influenced, so that the luminous efficiency is influenced. And the active area of the traditional LED structure has simple structural design and single luminescence, if multi-wavelength light is required to be emitted, multi-chip mixing or matched fluorescence mixing synthesis is required, the conversion efficiency is low, the packaging is complex, and the color rendering index is poor.
The multi-chip multi-primary color fluorescent powder-free LED has the problems of uneven light emission caused by difficult light mixing, high production cost caused by complicated driving circuit and the like. In order to solve the problems, the application adopts the quantum dot technology to realize that a single chip emits multi-wavelength LEDs, and utilizes a single LED chip to emit light with a wider spectrum or multiple colors, thereby reducing the packaging cost and improving the spectrum quality.
Disclosure of Invention
The invention aims to provide an LED epitaxial structure and a preparation method thereof, wherein a plurality of InN quantum dot active layers are arranged to realize multi-wavelength luminescence, density defects caused by a traditional structure are effectively restrained, and spectra are regulated by different quantum dot sizes, quantum dot well layer thicknesses and Al component settings, so that the LED device emits light uniformly.
To achieve the above object, the solution of the present invention is:
The LED epitaxial structure comprises a substrate, and an N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer which are sequentially arranged on the substrate in a first direction, wherein the quantum dot active layer comprises an InN blue light quantum dot active layer, an InN green light quantum dot active layer and an InN red light quantum dot active layer which are sequentially arranged along the first direction, and the first direction is perpendicular to the substrate.
The InN blue light quantum dot active layer comprises at least one first InN quantum dot well layer and a GaN barrier layer which are arranged in a stacked mode, the InN green light quantum dot active layer comprises at least one second InN quantum dot well layer and an Al xGa1-x N/GaN barrier layer which are arranged in a stacked mode, the InN red light quantum dot active layer comprises at least one third InN quantum dot well layer and an Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer which are arranged in a stacked mode, wherein x is more than or equal to 0.1 and less than or equal to y is more than or equal to 0.5, and the distribution of carriers is regulated by utilizing the barrier height of Al.
Optionally, the quantum dot diameters of the InN blue light quantum dot active layer, the InN green light quantum dot active layer and the InN red light quantum dot active layer are a, b and c in sequence, and a < b < c > is more than or equal to 2nm and less than or equal to 15nm.
Optionally, the thicknesses of the first InN quantum dot well layer, the second InN quantum dot well layer and the third InN quantum dot well layer are l, m and n in sequence, and l is more than or equal to 20nm and less than or equal to 50nm.
Optionally, the GaN barrier layer of the InN blue light quantum dot active layer has a thickness of 100nm, the number of trap barrier periods is 3-8, the Al xGa1-x N/GaN barrier layer of the InN green light quantum dot active layer has a thickness of 120nm, the ratio of Al xGa1-x N to GaN is 1:3, the number of trap barrier periods is 2-5, the Al yInzGa1-y-zN/AlwGa1- w N/GaN barrier layer of the InN red light quantum dot active layer has a thickness of 150nm, the ratio of Al yInzGa1-y-zN、AlwGa1-w N to GaN is 1:2:3, wherein z is more than or equal to 0.1 and less than or equal to 0.5, y is more than or equal to 0.1 and less than or equal to 0.5, and the trap barrier period is more than or equal to 2-5.
Optionally, an AlN buffer layer, a three-dimensional nucleation layer and a two-dimensional merging layer are further arranged between the substrate and the N-type semiconductor layer, a stress buffer layer is further arranged between the N-type semiconductor layer and the quantum dot active layer, and a P-AlGaN layer is further arranged between the quantum dot active layer and the P-type semiconductor layer.
The application also provides a preparation method of the LED epitaxial structure, which comprises the following steps:
Providing a substrate, and depositing and growing an N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer on the substrate in sequence in a first direction by adopting an MOCVD method;
The quantum dot active layer comprises an InN blue light quantum dot active layer, an InN green light quantum dot active layer and an InN red light quantum dot active layer which are sequentially grown along a first direction.
Optionally, the quantum dot active layer is grown by alternately introducing TMIn and NH 3 in a pulse growth mode, the growth pressure is 100 Torr-300 Torr, and the growth temperature is 500 ℃ to 650 ℃ including the end point value.
Optionally, the growth temperature, the NH 3/TMIn flux ratio and the growth deposition time of the InN blue light quantum dot active layer, the InN green light quantum dot active layer and the InN red light quantum dot active layer are all different, the flow rate of the introduced TMIn is 10 sccm-100 sccm, the flow rate of the NH 3 is 500 sccm-5000 sccm, and the end point values are included.
Optionally, the growth temperature of the InN blue light quantum dot active layer is 500-550 ℃, the flux ratio of NH 3 to TMIn is more than or equal to 200, the flow rate NH 3 is more than 2000sccm, and the growth deposition time is 10s-30s, including the endpoint value;
the growth temperature of the InN green light quantum dot active layer is 550-600 ℃, the flux ratio of NH 3 to TMIn is 50< NH 3/TMIn <200, and the growth deposition time is 30-50 s, including the end point value;
The growth temperature of the InN red light quantum dot active layer is 600-650 ℃, the flux ratio of NH 3 to TMIn is 10- 3/TMIn <50, the flow rate of introduced NH 3 is more than 50sccm, and the growth deposition time is 50-80 s, including the endpoint value.
After the scheme is adopted, the beneficial effects of the invention are as follows:
1. The InN quantum dot active layer structure is adopted to realize multi-wavelength light emission of a single LED chip, the structure is simple, and the quantum dot structure is used for eliminating the influence of dangling bonds and heterojunction isolation defects and the quadruple mechanism of growth dynamics optimization from quantum confinement reconstruction energy level and surface passivation, so that the density defect of the traditional LED active layer is restrained.
2. The InN quantum dot is directly used as a well layer structure of the active layer, the problems of cluster, segregation, luminescence peak broadening and the like caused by In/Ga phase separation are thoroughly solved, the mismatch degree of the InN and the GaN substrate is low, dislocation defects are relieved, the growth temperature of the InN quantum dot is lower than that of the conventional InGaN, desorption of In can be restrained, in incorporation is improved, in addition, the three-dimensional limited structure of the quantum dot also disperses interface stress through elastic strain relaxation, dislocation extension to the active region is restrained, and dislocation defects are further relieved.
3. The intrinsic luminous intensity of the blue light quantum dot is generally higher than that of the red light quantum dot, and the distribution of carriers is regulated by regulating the Al component of the barrier layer of each quantum dot active layer and regulating the barrier height of Al so as to improve the luminous uniformity. Specifically, the InN blue light quantum dot active layer is a pure GaN barrier layer, unnecessary potential barriers are prevented from being introduced by Al, the InN quantum dots and the GaN potential barriers form Type-II energy bands to be aligned, holes are localized in the quantum dots, electrons are distributed in the potential barrier areas, a built-in polarization field can be weakened, and radiation recombination efficiency is improved, the InN green light quantum dot active layer adopts a low Al component AlGaN/GaN composite barrier layer to balance carriers, the InN red light quantum dot active layer adopts a AlyInGaN/AlGaN/GaN composite barrier layer structure, the Al component is higher than that of the InN green light quantum dot active layer, a high electron potential barrier is formed, the electron utilization rate is high, the luminous intensity is improved, the defect of low intrinsic luminous intensity of the red light quantum dots is overcome, and the LED device emits light uniformly.
4. In a GaN-based LED structure, the electron concentration and mobility in the N-type semiconductor layer are several orders of magnitude higher than the hole concentration and mobility in the P-type semiconductor layer. Electrons are transported more easily to deeper quantum well active regions than holes, which can only be injected into the quantum wells near the P-type semiconductor layer. Therefore, for a multi-wavelength LED with a mixed multi-quantum dot structure, the light-emitting condition of the LED is directly determined by the transport condition of holes, and therefore, the light-emitting performance of the LED can be influenced by the growth sequence of quantum dots with different wavelengths and the structural design of a well layer of the quantum dots. Therefore, in order to regulate and control the luminous intensity In the three quantum dot wells, the luminous intensity In the three quantum dots is relatively average, and the well layer of the quantum dot with high In component is manufactured to be closer to the P-type semiconductor layer than the quantum dot well with low In component, so that the hole source is close to the hole source, and the hollow concentration In the quantum dot well with high In component is enhanced.
5. The application also adjusts the spectrum by controlling different sizes of quantum dots and different thicknesses of InN quantum dot trap layers, controls the trap layer thickness and the quantum dot diameter of InN blue light, green light and red light quantum dot active layers to be sequentially increased, and the forbidden band width is in inverse proportion to the InN quantum dot trap layer thickness and the quantum dot diameter.
6. The application controls the lower limit of the diameter of the quantum dot to be more than or equal to 2nm, avoids excessively high surface ratio, rapid increase of defect state density and excessively large energy level dispersion caused by undersize, further avoids carrier local runaway, and avoids disappearance of quantum confinement effect caused by excessively large size, the band gap is not adjustable, and further avoids increase of auger recombination rate.
7. The application controls the lower limit of the InN quantum dot well layer thickness of each quantum dot active layer to be more than or equal to 20nm, avoids the situation that carriers are not compounded and are diffused out of the active layer due to the fact that the thickness is too thin, ensures the carriers to be fully captured and compounded, avoids quantum tunneling leakage, and avoids the situation that the carrier transport path is too long due to the fact that the thickness is too thick, the probability of being captured by defects is increased, non-radiative composite loss and stress accumulation can be restrained, and high crystal quality is maintained.
Drawings
FIG. 1 is a schematic diagram of the epitaxial structure of comparative example 1 of the present invention;
fig. 2 is a schematic diagram of an epitaxial structure of embodiment 1 of the present invention;
Fig. 3 is a schematic structural diagram of a quantum dot active layer according to embodiment 2 of the present invention;
FIG. 4 is a flow chart of the preparation method of the invention.
Description of the reference numerals:
1. the semiconductor device comprises a substrate, a 2-AlN buffer layer, a 3-three-dimensional nucleation layer, a 4-two-dimensional merging layer, a 5-N semiconductor layer, a 6-stress buffer layer, a 7-quantum dot active layer, a 71-InN blue light quantum dot active layer, a 711-first InN quantum dot well layer, a 712-GaN barrier layer, a 72-InN green light quantum dot active layer, a 721-second InN quantum dot well layer, a 722-Al xGa1-x N/GaN barrier layer, a 73-InN red light quantum dot active layer, 731-third InN quantum dot well layer, 732-Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer, an 8-P-AlGaN layer, a 9-P semiconductor layer and a 10-quantum well active layer.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden based on the embodiments of the present application, are within the scope of the present application, which includes both endpoints.
As shown in fig. 1-2, the application provides an LED epitaxial structure, which comprises a substrate 1, and an N-type semiconductor layer 5, a quantum dot active layer 7 and a P-type semiconductor layer 9 sequentially arranged on the substrate in a first direction, wherein the first direction is perpendicular to the substrate, and can be a direction perpendicular to the substrate and deviating from the substrate, or a direction perpendicular to the substrate and approaching to the substrate, and the quantum dot active layer 7 comprises an InN blue light quantum dot active layer 71, an InN green light quantum dot active layer 72 and an InN red light quantum dot active layer 73 sequentially arranged along the first direction.
Quantum Dots (QDs) are used as nano-scale semiconductor functional materials, and the unique three-dimensional limited structure of the Quantum Dots can effectively inhibit or relieve density defects (such as point defects, dislocation, lattice distortion and the like) in the materials through various mechanisms, so that optical, electrical and other performances are improved. Density defects generally refer to locally disordered regions of a material in which the atomic/molecular arrangement deviates from the ideal lattice structure, common types including point defects, dislocations, lattice distortions, and the like. The application adopts the quantum dot structure as the active layer, eliminates the suspension bond from the quantum confinement reconstruction energy level and the surface passivation, and suppresses the density defect of the traditional LED active layer by a quadruple mechanism of heterojunction isolation defect influence and growth dynamics optimization.
In addition, the InN quantum dots are adopted as an active layer structure, so that the problems of clusters, segregation, luminescence peak broadening and the like caused by In/Ga phase separation are thoroughly solved, the mismatch degree of the InN and the GaN substrate is low, dislocation defects are relieved, the growth temperature of the InN quantum dots is lower than that of the conventional InGaN, the desorption of In is restrained, and the incorporation of In is improved.
Optionally, the light emission wavelengths of the InN blue light quantum dot active layer 71, the InN green light quantum dot active layer 72 and the InN red light quantum dot active layer 73 are 420nm-480nm, 500nm-560nm and 580nm-640nm respectively, the shorter the light emission wavelength is, the higher the intrinsic light emission intensity is, the highest the intrinsic light emission intensity of the InN blue light quantum dot active layer 71 is, and the lowest the intrinsic light emission intensity of the InN red light quantum dot active layer 73 is.
Alternatively, the three quantum dot active layers 7 can be superposition of an InN quantum dot well layer and a pure GaN barrier layer, but the distribution of carriers cannot be regulated through the barrier height of the barrier layer Al, the spectrum regulation effect is limited, and the luminous efficiency of the device is low.
As shown in fig. 3, as a preferred solution, the InN blue light quantum dot active layer 71 includes at least one first InN quantum dot well layer 711 and a GaN barrier layer 712 which are stacked, the InN green light quantum dot active layer 72 includes at least one second InN quantum dot well layer 721 and an Al xGa1-x N/GaN barrier layer 722 which are stacked, and the InN red light quantum dot active layer 73 includes at least one third InN quantum dot well layer 731 and an Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer 732 which are stacked, wherein x < y < w is greater than or equal to 0.1 and less than or equal to 0.5.
The InN blue light quantum dot active layer 71 adopts a pure GaN barrier layer, so that unnecessary potential barriers introduced by Al are avoided, in addition, inN quantum dots and GaN potential barriers form Type-II energy bands to be aligned, holes are localized in the quantum dots, electrons are distributed in the potential barrier region, a built-in polarization field can be weakened, radiation recombination efficiency is improved, and luminous efficiency is improved.
The InN green light quantum dot active layer 72 adopts an AlGaN/GaN composite barrier layer with low Al component to balance carriers, the InN red light quantum dot active layer 73 adopts an AlInGaN/AlGaN/GaN composite barrier layer structure, the Al component of the InN green light quantum dot active layer 72 is higher than that of the InN green light quantum dot active layer 72, a high electron barrier is formed, the electron utilization rate is high, the luminous intensity is improved, the defect of low intrinsic luminous intensity of the red light quantum dot is overcome, and the luminous intensity of the LED device is uniform.
Optionally, the quantum dot diameters of the InN blue light quantum dot active layer 71, the InN green light quantum dot active layer 72 and the InN red light quantum dot active layer 73 are a, b and c in sequence, a < b < c < 15nm is more than or equal to 2nm, the thicknesses of the first InN quantum dot well layer 711, the second InN quantum dot well layer 721 and the third InN quantum dot well layer 731 are l, m and n in sequence, and l < m < n < 50nm is more than or equal to 20 nm. The application also adjusts the spectrum by controlling different sizes of quantum dots and different thicknesses of InN quantum dot well layers, and particularly controls the thickness of InN quantum dot well layers and the diameters of InN blue light, green light and red light quantum dot active layers to be sequentially increased, and the forbidden band width is in inverse relation with the thickness of InN quantum dot well layers and the diameters of quantum dots.
Optionally, the thickness of the GaN barrier layer 712 of the InN blue light quantum dot active layer 71 is 100nm, the number of well barrier periods is 3-8, the thickness of the Al xGa1-x N/GaN barrier layer 722 of the InN green light quantum dot active layer 72 is 120nm, the thickness ratio of Al xGa1-x N to GaN is 1:3, the number of well barrier periods is 2-5, the thickness of the Al yInzGa1-y- zN/AlwGa1-w N/GaN barrier layer 732 of the InN red light quantum dot active layer 73 is 150nm, the thickness ratio of Al yInzGa1-y-zN、AlwGa1-w N to GaN is 1:2:3, wherein z is more than or equal to 0.1 and less than or equal to 0.5, y is more than or equal to 0.1 and less than or equal to 0.5, and the number of well barrier periods is 2-5.
Preferably, the quantum dot diameter a=5 nm of the InN blue light quantum dot active layer 71, the thickness l=20 nm of the first InN quantum dot well layer 711, the number of well barrier periods is 5, the quantum dot diameter b=8 nm of the InN green light quantum dot active layer 72, the thickness m=35 nm of the second InN quantum dot well layer 721, the al composition x=0.1, the number of well barrier periods is 3, the quantum dot diameter b=8 nm of the InN red light quantum dot active layer 73, the thickness m=35 nm of the third InN quantum dot well layer 731, the al composition y=0.3, w=0.4, the in composition z=0.3, and the number of well barrier periods is 3. The spectrum regulation effect of the quantum dot active layer 7 with the parameter value is good, and the luminous efficiency of the manufactured device can reach 200lm/W.
Optionally, an AlN buffer layer 2, a three-dimensional nucleation layer 3, and a two-dimensional merging layer 4 are further disposed between the substrate 1 and the N-type semiconductor layer 5, a stress buffer layer 6 is further disposed between the N-type semiconductor layer 5 and the quantum dot active layer 7, and a P-AlGaN layer 8 is further disposed between the quantum dot active layer 7 and the P-type semiconductor layer 9, so as to form an epitaxial structure with complete functions and optimal performance.
The application also provides a preparation method of the LED epitaxial structure, which comprises the following steps:
The method comprises the steps of providing a substrate 1, wherein the substrate 1 can be any one of a Si substrate, a PSS sapphire substrate and a SiC substrate, and sequentially depositing and growing an AlN buffer layer 2, a three-dimensional nucleation layer 3, a two-dimensional merging layer 4, an N-type semiconductor layer 5, a stress buffer layer 6, a quantum dot active layer 7, a P-AlGaN layer 8 and a P-type semiconductor layer 9 on the substrate 1 in a first direction by adopting a Metal Organic Chemical Vapor Deposition (MOCVD) method, wherein the quantum dot active layer 7 comprises an InN blue light quantum dot active layer 71, an InN green light quantum dot active layer 72 and an InN red light quantum dot active layer 73 which are sequentially grown in the first direction.
Specifically, the InN blue light quantum dot active layer 71 includes at least one first InN quantum dot well layer 711 and a GaN barrier layer 712 that alternately grow, the InN green light quantum dot active layer 72 includes at least one second InN quantum dot well layer 721 and an Al xGa1-x N/GaN barrier layer 722 that alternately grow, and the InN red light quantum dot active layer 73 includes at least one third InN quantum dot well layer 731 and an Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer 732 that alternately grow, wherein x < y < w > is 0.1 < 0.5, the distribution of carriers is adjusted by using the barrier height of Al, the luminous intensity of different wavelengths is adjusted, and further, the spectrum is adjusted, so that the adjustment of different spectrums is realized.
Optionally, the quantum dot diameters of the InN blue light quantum dot active layer 71, the InN green light quantum dot active layer 72 and the InN red light quantum dot active layer 73 are a, b and c in sequence, the growth thicknesses of the first InN quantum dot well layer 711, the second InN quantum dot well layer 721 and the third InN quantum dot well layer 731 are l, m and n in sequence, a < b < c > is more than or equal to 2nm and less than or equal to 15nm, l < m < n > is more than or equal to 20nm and less than or equal to 50nm, and the spectrum is further adjusted by adjusting the thickness of the Inn quantum dot well layers and the quantum dot diameters of the quantum dot active layers 7, so that the LED device emits light uniformly.
Optionally, the quantum dot active layer 7 is grown by alternately introducing TMIn and NH 3 in a pulse growth mode, the growth pressure is 100 Torr-300 Torr, the growth temperature is 500 ℃ to 650 ℃, different quantum dot sizes and InN quantum dot well layer thickness sizes are realized through different growth temperatures, V/III flux ratios (NH 3/TMIn flux ratios) and growth deposition time, the TMIn flow is 10 sccm-100 sccm, the NH 3 flow is 500 sccm-5000 sccm, and the specific growth process of each quantum dot active layer is as follows:
Growing InN blue light quantum dot active layer 71, wherein the growth temperature is 500-550 ℃, the flux ratio of NH 3 and TMIn is more than or equal to 200 (high V/III flux ratio), the flow rate NH 3 is more than 2000sccm (rich N condition), the growth deposition time is 10s-30s, the thickness of GaN barrier layer 712 is 100nm, and the number of trap barrier periods is 3-8;
Growing an InN green light quantum dot active layer 72, wherein the growth temperature is 550-600 ℃, the flux ratio of NH 3 to TMIn is 50< NH 3/TMIn <200, the growth deposition time is 30s-50s, the total thickness of an Al xGa1-x N/GaN barrier layer 722 is 120nm, the thickness ratio is 1:3, and the number of trap barrier periods is 2-5;
InN red light quantum dot active layer 73 is grown, the growth temperature is 600-650 ℃, the flux ratio of NH 3 to TMIn is 10- 3/TMIn <50 (low V/III flux ratio), the flow rate NH 3 is more than 50sccm (In-rich condition), the growth deposition time is 50s-80s, the total thickness of Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer 732 is 150nm, the thickness ratio is 1:2:3, and the number of trap barrier periods is 1-3.
Through the different growth temperature, flux ratio and growth deposition time, the size and thickness control of a < b < c < 15nm, l < m < n < 50nm of 2nm and less than or equal to 20nm are realized. In addition, the in-situ growth epitaxial structure is formed by MOCVD epitaxial deposition, the growth rate is high, the cost is low, the large-scale mass production can be realized, the quantum dot size and the thickness of the InN quantum dot well layer are convenient to adjust, and the control precision is high. Specific growth processes of other epitaxial layers except the quantum dot active layer 7 are described in detail below.
As shown in fig. 4, the following further illustrates the effects of the preparation method and core scheme according to the present invention by specific examples and comparative examples:
comparative example 1:
Comparative example 1 is a conventional preparation method of an LED epitaxial structure, in which an active layer is a quantum well active layer 10 structure formed by stacking a InCaN well layer and a CaN barrier layer, MOCVD equipment is adopted, trimethylgallium TMGa and triethylgallium TEGa are used as Ga sources, ammonia gas NH 3 is used as N sources, trimethylindium TMIn is used as In sources, trimethylaluminum TMAl is used as Al sources, H 2 and N 2 are used as carrier gases, N-type and P-type doping sources are silane SiH 4 and magnesium-cyclopentadienyl CP 2 Mg respectively, a sapphire substrate is used, and a graphite disc is used as a substrate carrier for deposition growth, as shown In fig. 1, the preparation method specifically comprises the following steps:
S1, growing an AlN buffer layer 2 on a substrate 1, namely, introducing H 2 at a high temperature of 1150 ℃ (the temperature range is 900 ℃ -1150 ℃) for 5min for hydrogenation treatment, removing impurities, scratches, particles and the like on the surface of the substrate, then introducing TMAL and SiH 4、NH3、H2、N2 at a high temperature of 1000 ℃ (the temperature range is 900 ℃ -1150 ℃) for growing the AlN buffer layer 2, wherein the thickness is 25nm (the thickness range is 5-50 nm), and the molar ratio of Si and Al is 0.2 (the molar ratio range is 0.05-0.5).
S2, growing a three-dimensional nucleation layer 3 on the AlN buffer layer 2, namely introducing NH 3、H2、N2 at 900 ℃ (the temperature range is 800 ℃ -1000 ℃), wherein the NH 3 component is 20% (the component range is 30% -80%), the growth time is 1min (the time range is 0.5 min-3 min), and using lattice mismatch between GaN and AlN as a driving force to realize a three-dimensional island growth mode by using deposition decomposition in a small ammonia atmosphere.
And S3, growing a two-dimensional combined layer 4 on the three-dimensional nucleation layer 3, namely introducing NH 3、H2、N2 at 1100 ℃ (the temperature range is 900 ℃ -1200 ℃), wherein the NH 3 component is 80% (the component range is 70% -100%), the growth time is 2min (the time range is 0.5 min-3 min), and realizing a lateral growth mode by utilizing diffusion under the high-temperature large ammonia atmosphere, so that the three-dimensional island-shaped combined GaN plane is reduced in dislocation density.
And S4, growing an N-type semiconductor layer 5 on the two-dimensional merging layer 4, wherein the N-type semiconductor layer is an N-type gallium nitride layer, TMGa and SiH 4、NH3、H2、N2 are introduced, the growth thickness is 2000nm (the thickness range is 1500 nm-2500 nm), the growth temperature is 1050 ℃ (900 ℃ -1200 ℃), and the doping concentration of SiH 4 is 2E 18/cm3.
And S5, growing a stress buffer layer 6 on the N-type semiconductor layer 5, wherein TEGa, TMIn, NH 3、H2、N2 is introduced, an InGaN/GaN superlattice structure with 30 (25-35) periods is grown, the thickness of single InGaN is 5nm, the thickness of single GaN is 2nm, the total thickness of the stress buffer layer 6 is 210nm (150-250 nm), the temperature of an InGaN well layer is 800 ℃ (700-850 ℃), and the temperature of a GaN barrier layer is 880 ℃ (800-1000 ℃).
And S6, growing a quantum well active layer 10 on the stress buffer layer 6, wherein TEGa, TMIn, siH 4、NH3、H2、N2 is introduced, the thickness of a single InGaN well layer is 3nm, the thickness of a single GaN barrier layer is 11nm, the total thickness is 14nm (the thickness range is 10 nm-16 nm), the temperature of the InGaN well layer is 780 ℃ (the temperature range is 700 ℃ -850 ℃), the temperature of the GaN barrier layer is 900 ℃ (the temperature range is 800 ℃ -1000 ℃), and the number of well barrier periods is 8 (the period range is 3-10).
S7, growing a P-AlGaN layer 8 on the quantum well active layer 10, wherein TMAl, TMGa, CP 2Mg、NH3、H2 is introduced, the growth thickness is 200 nm (the thickness range is 150-250 nm), the growth pressure is 100 torr, the growth temperature is 900 ℃ in the atmosphere of N 2 (the temperature range is 850-1050 ℃), the growth rate is 20A/S, the doping concentration of Mg is 5E 19/cm3, and the Al component x is 20% (the component range is 0-50%).
And S8, growing a P-type semiconductor layer 9 on the P-AlGaN layer 8, wherein the P-type semiconductor layer is a P-type gallium nitride layer, TMGa and CP 2Mg、NH3、H2、N2 are introduced, the growth thickness is 400nm (the thickness range is 200-600 nm), the growth temperature is 1050 ℃ (the temperature range is 800-1200 ℃), and the doping concentration of Mg is 1E 20/cm3 (the concentration range is 1E 19/cm3-4E20/cm3).
After the steps are finished, cooling annealing treatment is carried out, then the grown epitaxial wafer is tested, photoelectric parameter test is carried out through EL, and the luminous efficiency of the device obtained through test is 50lm/W-130lm/W, so that the traditional LED structure is low in luminous efficiency, simple in structural design and single in luminous, multi-chip mixing or matched fluorescent mixing synthesis is needed if multi-wavelength light needs to be emitted, the conversion efficiency is low, the packaging is complex, and the color rendering index is poor.
Example 1:
The active layer of example 1 adopts a quantum dot active layer 7 structure, and the growth process of other epitaxial layers is the same as that of comparative example 1 except for the active layer. As shown in fig. 2, the quantum dot active layer 7 in embodiment 1 includes an InN blue light quantum dot active layer 71, an InN green light quantum dot active layer 72 and an InN red light quantum dot active layer 73, wherein the three quantum dot active layers are all periodic stacks of an InN quantum dot well layer and a GaN barrier layer, and the growth process is that TEGa, TMIn, siH 4、NH3、H2、N2 is introduced, the temperature of the quantum dots in the InN well region is 500-650 ℃, the growth temperature of the barrier region is 700-850 ℃, and the growth pressure is 100-300 torr.
In example 1, compared with comparative example 1, the single chip emits multiple wavelengths by using the quantum dot technology, but the well barrier structures of the quantum dot active layers 7 are the same, the barrier layers are all GaN, the distribution of carriers cannot be regulated by the barrier height of the barrier layers Al, quantum dots with different sizes and different InN quantum dot well layer thicknesses cannot be obtained without designing different growth temperatures, V/III flux ratios and deposition times, the light emission efficiency of the manufactured device is tested to be 150lm/W, the light emission efficiency is still lower, and the market demand cannot be satisfied.
Example 2:
The growth process of the quantum dot active layer 7 in this embodiment is different from that of the quantum dot active layer 7 in embodiment 1, the growth process of other epitaxial layers is the same as that of embodiment 1, as shown in fig. 3, the barrier layer structure of each InN quantum dot active layer in this embodiment is different, the InN blue light quantum dot active layer 71 includes at least one first InN quantum dot well layer 711 and a GaN barrier layer 712 which are stacked, the InN green light quantum dot active layer 72 includes at least one second InN quantum dot well layer 721 and an Al xGa1-x N/GaN barrier layer 722 which are alternately grown, the InN red light quantum dot active layer 73 includes at least one third InN quantum dot well layer 731 and an Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer 732 which are alternately grown, and different quantum dot size and well layer thickness control are realized through different growth temperatures, flux ratios and growth deposition times, and the growth process of the quantum dot active layer is as follows:
Under the pressure of 100 Torr-300 Torr, TMIn and NH 3 are alternately introduced in a pulse growth mode, the temperature of the quantum dots in the well region is 500-650 ℃, the growth temperature of the barrier region is 700-850 ℃, the inflow rate of the TMIn is 10 sccm-100 sccm, and the inflow rate of NH 3 is 500 sccm-5000 sccm, and the method comprises the following specific steps:
Firstly, growing an InN blue light quantum dot active layer 71, wherein the growth temperature is 500-550 ℃, the V/III specific flux ratio is that NH 3/TMIn is more than or equal to 200, the inlet flow NH 3 is more than 2000sccm, the deposition time is 10s-30s, the quantum dot size is a=5 nm, the thickness of a first InN quantum dot well layer 711 is l=20 nm, the thickness of a GaN barrier layer 712 is 100nm, and the number of well barrier periods is 5;
Secondly, growing an InN green light quantum dot active layer 72, wherein the growth temperature is 550-600 ℃, the V/III flux ratio is 50< NH 3/TMIn <200, the deposition time is 30s-50s, the quantum dot size is b=8nm, the thickness of a second InN quantum dot well layer 721 is m=35nm, the total thickness of an Al xGa1-x N/GaN barrier layer 722 is 120nm, the thickness ratio is 1:3, the Al component is x=0.1, and the number of well barrier periods is 3;
Finally, growing an InN red light quantum dot active layer 73, wherein the growth temperature is 600-650 ℃, the V/III flux ratio is 10-or-less NH 3/TMIn <50, TMIn >50sccm, the deposition time is 50s-80s, the quantum dot size is c=12 nm, the thickness of the third InN quantum dot well layer 731 is n=50 nm, the total thickness of the Al yInzGa1-y-zN/AlwGa1-w N/GaN barrier layer 732 is 150nm, the thickness ratio is 1:2:3, the Al component is y=0.3, z=0.4, y < z, the In component is w=0.3, and the number of well barrier periods is 2.
In the embodiment 2, compared with the embodiment 1, quantum dots with different sizes and In quantum dot well layers with different thicknesses are obtained by designing different growth temperatures, V/III flux ratios and deposition times, multi-wavelength luminescence and spectrum regulation are realized, and the distribution of carriers is regulated and controlled by blocking electrons by an Al barrier layer, so that the spectrum proportion of different wavebands is regulated and controlled, a proper color temperature spectrum is realized, the spectrum and the color temperature are adjustable, the luminescence efficiency of the manufactured device can be up to 200lm/W through testing, the luminescence efficiency is improved, and the market demand is met.
It should be noted that the thicknesses of the substrate 1, the AlN buffer layer 2, the three-dimensional nucleation layer 3, the two-dimensional merging layer 4, the N-type semiconductor layer 5, the stress buffer layer 6, the quantum dot active layer 7, the P-AlGaN layer 8, and the P-type semiconductor layer 9 shown in the drawings of the present application are merely examples, and do not represent the actual thicknesses thereof. The actual proportions among the substrate 1, the AlN buffer layer 2, the three-dimensional nucleation layer 3, the two-dimensional merging layer 4, the N-type semiconductor layer 5, the stress buffer layer 6, the quantum dot active layer 7, the P-AlGaN layer 8, and the P-type semiconductor layer 9 are not just references as shown in the drawings.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
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