LED epitaxial structure and preparation method thereof

Abstract

The invention provides an LED epitaxial structure and a preparation method thereof, the epitaxial structure is deposited and grown by adopting an MOCVD method, and the 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 in the first direction, the multiple InN quantum dot active layers are arranged to achieve multi-wavelength light emitting, and the density defect caused by a traditional structure is effectively restrained; and the spectrum is adjusted by setting different quantum dot sizes, quantum dot well layer thicknesses and Al components, so that the LED device emits light uniformly.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor optoelectronics, and particularly relates to an LED epitaxial structure and a preparation method thereof. BACKGROUND

[0002] In recent years, LED devices are widely used in lighting, display, medical treatment and visible light communication fields due to their small size, high efficiency, long service life and other advantages. With the progress of science and technology and the improvement of people's living standards, people's requirements for lighting are no longer high-brightness and high-efficiency lighting modes, but more energy-saving, environmentally friendly, healthy and intelligent lighting modes that are people-oriented. Full-spectrum phosphor-free lighting is one of the development trends of LED lighting technology, which can improve the spectral quality of LED lighting and improve human life. At present, the main way to realize multiple wavelengths is to use multi-chip multi-primary color LEDs.

[0003] The traditional LED structure has an active region formed by the superposition of an InGaN well layer and a GaN barrier layer. The longer the light-emitting wavelength is, the higher the required In component is, and the lower the light-emitting efficiency is. The wavelengths of blue light, green light and red light increase in turn, the required In components increase in turn, and the light-emitting efficiency decreases in turn. Therefore, it is necessary to increase the light-emitting efficiency of red light. However, in the existing GaN-based LED system, the realization of high-efficiency red light emission faces many technical challenges, and the core difficulty lies in the contradiction between the intrinsic properties of high-In-content InGaN (x>0.4) and growth / device design. x Ga 1-x N material (x>0.4), which specifically includes the following aspects: 1. Red light emission requires an In component x>0.4 (corresponding to a band gap <2.0 eV), but high-In-content material growth is difficult, which is specifically reflected in that: high-In-content InGaN has a serious lattice mismatch with a GaN substrate, which can increase dislocations and significantly reduce light-emitting efficiency, and In atoms tend to gather in InGaN clusters, which can destroy the uniformity of the material, cause light-emitting peak broadening and wavelength drift; in addition, the vapor pressure of In is much higher than that of Ga, and high-In-content growth needs to strictly control the supply rate of group III source (TMIn). If the supply is insufficient, In atom vacancies are easily formed; if the supply is excessive, In atoms cannot be uniformly doped into the lattice due to the weak migration ability of In atoms (the surface diffusion length is only about 0.1 nm), which can cause In segregation (local In content >0.5) or three-dimensional island growth (instead of ideal two-dimensional layer growth), further deteriorating the crystalline quality.

[0004] 2. Even if high-quality high-In-composition InGaN is obtained by overcoming the growth difficulties, its intrinsic physical properties still significantly limit the performance of red LEDs: the strong polarization effect of the GaN system leads to carrier separation, which directly leads to a decrease in the radiative recombination rate, and the electron mobility and hole mobility of high-In-composition InGaN are both significantly lower than those of GaN, and low mobility leads to difficulty in effectively injecting carriers, especially holes, into the quantum well, and after injection, the carriers are easily captured by defects, further reducing the radiative recombination efficiency. In addition, uneven carrier transport between quantum wells (excessive carrier concentration in high-In-composition well regions) can cause Auger recombination, exacerbating the degradation of light-emitting efficiency.

[0005] Therefore, the stress of the traditional well-barrier superposition structure is large, lattice mismatch is easy to occur, which affects the distribution of carriers and has density defects, affecting the light-emitting efficiency. Moreover, the active region structure of the traditional LED structure is simple in design and single in light emission. If multiple wavelengths of light need to be emitted, multiple chips need to be mixed or matched with fluorescent light to synthesize, which has low conversion efficiency, complex packaging, and poor color rendering index.

[0006] Moreover, the multi-chip multi-primary color fluorescent powder-free LED has the problems of uneven light emission due to light mixing difficulty, and high production cost due to complex driving circuit. In order to solve the above problems, the quantum dot technology is used to realize single-chip multi-wavelength LED, and a single LED chip is used to emit a wide spectrum or multiple colors of light, thereby reducing the packaging cost and improving the spectral quality. SUMMARY

[0007] The purpose of the present application is to provide an LED epitaxial structure and a preparation method thereof, a plurality of InN quantum dot active layers are arranged to realize multi-wavelength light emission, and density defects caused by traditional structures are effectively suppressed, and the spectrum is adjusted by different quantum dot sizes, quantum dot well layer thicknesses, and Al composition settings, so that the LED device emits light uniformly.

[0008] To achieve the above purpose, the solution of the present application is as follows: The present application provides an LED epitaxial structure, comprising a substrate, and an N-type semiconductor layer, a quantum dot active layer, and a P-type semiconductor layer arranged in a first direction on the substrate; 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 arranged in the first direction, and the first direction is perpendicular to the substrate.

[0009] The InN blue light quantum dot active layer comprises at least one first InN quantum dot well layer and a GaN barrier layer arranged in layers, the InN green light quantum dot active layer comprises at least one second InN quantum dot well layer and an Al x Ga 1-xInN red quantum dot active layer, the InN red quantum dot active layer comprises at least a third InN quantum dot well layer and Al y In z Ga 1-y-z N / Al w Ga 1-w N / GaN barrier layer, wherein 0.1≤x<y<w≤0.5, the distribution of carriers is adjusted by the barrier height of Al.

[0010] Optionally, the quantum dot diameters of the InN blue quantum dot active layer, the InN green quantum dot active layer and the InN red quantum dot active layer are a, b and c respectively, and 2nm≤a<b<c≤15nm.

[0011] 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 respectively, and 20nm≤l<m<n≤50nm.

[0012] Optionally, the thickness of the GaN barrier layer of the InN blue quantum dot active layer is 100nm, and the number of well-barrier periods is 3-8; the thickness of the Al x Ga 1-x N / GaN barrier layer of the InN green quantum dot active layer is 120nm, and the number of well-barrier periods is 2-5; the thickness of the Al x Ga 1-x N / GaN barrier layer of the InN red quantum dot active layer is 150nm, and the number of well-barrier periods is 2-5. y In z Ga 1-y-z N / Al w Ga 1- w N / GaN barrier layer of the InN red quantum dot active layer is 150nm, and the number of well-barrier periods is 2-5. y In z Ga 1-y-z N, AlwGa 1-w N and GaN is 1:2:3, wherein 0.1<z≤0.5, y<z, 0.1≤w≤0.5, and the number of well-barrier periods is 2-5.

[0013] 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.

[0014] The application further provides a preparation method of the LED epitaxial structure, comprising: A substrate is provided, and a N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer are sequentially deposited in a first direction on the substrate by using a MOCVD method. The quantum dot active layer comprises an InN blue quantum dot active layer, an InN green quantum dot active layer and an InN red quantum dot active layer sequentially grown in the first direction.

[0015] Optionally, the quantum dot active layer is grown by alternately inputting TMIn and NH3 in a pulse growth mode, the growth pressure is 100 Torr-300 Torr, and the growth temperature is 500℃-650℃, including the end point values.

[0016] Optionally, the growth temperature, the NH3 / TMIn flux ratio and the growth deposition time of the InN blue quantum dot active layer, the InN green quantum dot active layer and the InN red quantum dot active layer are different, the flow rate of TMIn is 10sccm-100sccm, the flow rate of NH3 is 500sccm-5000sccm, and the end point values are included.

[0017] Optionally, the growth temperature of the InN blue quantum dot active layer is 500℃-550℃, the NH3 and TMIn flux ratio is NH3 / TMIn≥200, the flow rate of NH3 is >2000sccm, and the growth deposition time is 10s-30s, including the end point values. The growth temperature of the InN green quantum dot active layer is 550℃-600℃, the NH3 and TMIn flux ratio is 50 The growth temperature of the InN red quantum dot active layer is 600℃-650℃, the NH3 and TMIn flux ratio is 10≤NH3 / TMIn<50, the flow rate of NH3 is >50sccm, and the growth deposition time is 50s-80s, including the end point values.

[0018] After the above scheme is used, the application has the following advantages: 1. The InN quantum dot active layer structure is used to realize single LED chip multi-wavelength light emission, and the structure is simple.

[0019] 2、The application directly uses InN quantum dots as the well layer structure of the active layer, completely eliminates the problems of clusters, segregation and emission peak broadening caused by In / Ga phase separation, and reduces the mismatch degree of InN and GaN substrate, slows down the dislocation defects, the growth temperature of InN quantum dots is lower than that of traditional InGaN, which can inhibit the desorption of In and improve the incorporation of In. In addition, the three-dimensional confined structure of quantum dots also disperses the interface stress through elastic strain relaxation, inhibits the extension of dislocations to the active region, and further slows down the dislocation defects.

[0020] 3、The intrinsic emission intensity of blue quantum dots is usually higher than that of red quantum dots. The application adjusts the Al component of each quantum dot active layer barrier layer to adjust the distribution of carriers through the barrier height of Al, so as to improve the emission uniformity. Specifically, the InN blue quantum dot active layer is a pure GaN barrier layer, avoiding unnecessary barriers caused by Al, and the InN quantum dots and GaN barrier form a Type-II band alignment, the holes are localized in the quantum dots, and the electrons are distributed in the barrier region, which can weaken the built-in polarization field and improve the radiation recombination efficiency. The InN green quantum dot active layer adopts a low Al component AlGaN / GaN composite barrier layer to balance the carriers, and the InN red quantum dot active layer adopts an AlyInGaN / AlGaN / GaN composite barrier layer structure, and the Al component is higher than that of the InN green quantum dot active layer, forming a high electron barrier, high electron utilization rate, improving the emission intensity, making up for the defect of low intrinsic emission intensity of red quantum dots, and making the emission of the LED device uniform.

[0021] 4、In the 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. Therefore, electrons are more easily transported to the deeper quantum well active region than holes, and holes can only be injected into the quantum well close to the P-type semiconductor layer. Therefore, for a multi-wavelength LED containing a mixed multi-quantum dot structure, the transport of holes directly determines the LED emission, and therefore the growth order of different wavelength quantum dots and the design of the well layer structure will affect the emission performance. Therefore, in order to regulate the emission intensity in the three quantum dot wells and make the emission intensity in the three quantum dots relatively average, the well layer of the high In component quantum dot is made closer to the P-type semiconductor layer than the well of the low In component quantum dot during production, so as to be close to the hole source and enhance the hole concentration in the high In component quantum dot well. Thus, the quantum dot active layer is grown in the order of blue, green and red.

[0022] 5、The application also adjusts the spectrum by controlling the different sizes of quantum dots and the different thicknesses of InN quantum dot well layers, the well layer thickness and the quantum dot diameter of the InN blue light, green light and red light quantum dot active layers are increased in turn, the band gap is inversely proportional to the well layer thickness and the quantum dot diameter of the InN quantum dot, the InN quantum dot well layer thickness and the quantum dot diameter of the InN red light quantum dot active layer are set to be the largest in the application, the band gap can be reduced, the light emitting intensity is improved, the defect of low intrinsic light emitting intensity of the red light quantum dot is further compensated, and the light emitting of the LED device is uniform.

[0023] 6、The diameter lower limit of the quantum dots is controlled to be greater than or equal to 2 nm in the application, the size is too small to cause the surface ratio to be too high, the defect state density to increase sharply, and the energy level dispersion to be too large, and then the carrier local controllability is avoided; the diameter upper limit is controlled to be less than or equal to 15 nm, the size is too large to cause the quantum confinement effect to disappear, the band gap to be unadjustable, the carrier local controllability to be weakened, and then the Auger recombination rate is avoided to increase.

[0024] 7、The InN quantum dot well layer thickness lower limit of each quantum dot active layer is controlled to be greater than or equal to 20 nm in the application, the thickness is too thin to cause the carriers to diffuse out of the active layer before being recombined, the carriers are fully captured and recombined, and quantum tunneling leakage is avoided; the thickness upper limit is controlled to be less than or equal to 50 nm, the thickness is too large to cause the carrier transport path to be too long, the probability of being captured by defects to increase, the non-radiative recombination loss and stress accumulation to be inhibited, and the high crystal quality to be maintained. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is an epitaxial structure schematic diagram of the present application comparative example 1; Figure 2 It is an epitaxial structure schematic diagram of the present application comparative example 1; Figure 3 It is a quantum dot active layer structure schematic diagram of the present application comparative example 2; Figure 4 It is a preparation method flow chart of the present application.

[0026] Label explanation: 1, substrate; 2, AlN buffer layer; 3, three-dimensional nucleation layer; 4, two-dimensional merging layer; 5, N-type semiconductor layer; 6, stress buffer layer; 7, quantum dot active layer; 71, InN blue light quantum dot active layer; 711, first InN quantum dot well layer; 712, GaN barrier layer; 72, InN green light quantum dot active layer; 721, second InN quantum dot well layer; 722, Al x Ga 1-x N / GaN barrier layer; 73, InN red light quantum dot active layer; 731, third InN quantum dot well layer; 732, Al y In z Ga 1-y-zN / Al w Ga 1-w N / GaN barrier layer; 8, P-AlGaN layer; 9, P-type semiconductor layer; 10, quantum well active layer. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application, and the range of the present application includes two end values.

[0028] As Figures 1-2 shown, the present application provides an LED epitaxial structure, comprising a substrate 1, and sequentially arranged in a first direction on the substrate are an N-type semiconductor layer 5, a quantum dot active layer 7, and a P-type semiconductor layer 9, the first direction is perpendicular to the substrate, which can be a direction perpendicular to the substrate and away from the substrate, or a direction perpendicular to the substrate and close to the substrate; 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 arranged in the first direction.

[0029] Quantum dots (QDs) as a kind of nanometer scale semiconductor functional material, its unique three-dimensional confined structure can effectively inhibit or alleviate the density defects (such as point defects, dislocations, lattice distortion, etc.) in the material, so as to improve the optical, electrical and other properties. Density defects usually refer to the local disordered area in which the atomic / molecular arrangement deviates from the ideal lattice structure, and the common types include point defects, dislocations, lattice distortion, etc. The present application adopts quantum dot structure as the active layer, which inhibits the density defects of the traditional LED active layer through four mechanisms of quantum confinement reconfiguration energy level, surface passivation to eliminate dangling bonds, heterojunction isolation of defect influence, and growth kinetics optimization.

[0030] In addition, the present application adopts InN quantum dots as the active layer structure, which completely eliminates the problems of clustering, segregation and emission peak broadening caused by In / Ga phase separation, and the InN and GaN substrate mismatch degree is low, which slows down the dislocation defects, the growth temperature of InN quantum dots is also lower than that of traditional InGaN, which inhibits the desorption of In and improves the incorporation of In.

[0031] Optionally, the 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 emission wavelength, the higher the intrinsic luminescence intensity. The intrinsic luminescence intensity of the InN blue light quantum dot active layer 71 is the highest, and the intrinsic luminescence intensity of the InN red light quantum dot active layer 73 is the lowest. The present application regulates the spectrum by controlling the Al component, the thickness of the InN quantum dot well layer, and the size of the quantum dots to improve the luminescence intensity of the InN red light quantum dot active layer 73 and make the light emission of the LED device uniform.

[0032] Optionally, the three-layer quantum dot active layer 7 can be a superposition of an InN quantum dot well layer and a pure GaN barrier layer. However, this setting cannot adjust the carrier distribution by the barrier height of the Al barrier layer, the effect of adjusting the spectrum is limited, and the device luminescence efficiency is not high.

[0033] like Figure 3 As shown, as a preferred solution, the InN blue quantum dot active layer 71 includes at least a first InN quantum dot well layer 711 and a GaN barrier layer 712 stacked; the InN green quantum dot active layer 72 includes at least a second InN quantum dot well layer 721 and an Al x Ga 1-x N / GaN barrier layer 722; the InN red light quantum dot active layer 73 includes at least a third InN quantum dot well layer 731 and an Al y In z Ga 1-y-z N / A w Ga 1-w N / GaN barrier layer 732, where 0.1≤x <y<w≤0.5。

[0034] The InN blue light quantum dot active layer 71 adopts a pure GaN barrier layer, which avoids the unnecessary potential barrier introduced by Al. Moreover, the InN quantum dots and the GaN barrier form Type-II band alignment, the holes are localized in the quantum dots, and the electrons are distributed in the barrier region, which can weaken the built-in polarization field, improve the radiation recombination efficiency, and improve the luminous efficiency.

[0035] The InN green quantum dot active layer 72 uses an AlGaN / GaN composite barrier layer with a low Al component to balance carriers, and the InN red quantum dot active layer 73 uses an AlInGaN / AlGaN / GaN composite barrier layer structure, whose Al component is higher than that of the InN green quantum dot active layer 72, forming a high electron potential barrier, high electron utilization, and improved luminous intensity, which compensates for the defect of low intrinsic luminous intensity of red quantum dots and makes the LED device emit light uniformly.

[0036] Optionally, the quantum dot diameters of the InN blue quantum dot active layer 71, the InN green quantum dot active layer 72 and the InN red quantum dot active layer 73 are a, b and c respectively, and 2nm≤a<b<c≤15nm, 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 respectively, and 20nm≤l<m<n≤50nm. The present application also adjusts the spectrum by controlling the different sizes of the quantum dots and the different thicknesses of the InN quantum dot well layers. Specifically, the InN quantum dot well layer thickness and the quantum dot diameter of the InN blue, green and red quantum dot active layers are increased in turn, the band gap is inversely proportional to the InN quantum dot well layer thickness and the quantum dot diameter, the InN quantum dot well layer thickness and the quantum dot diameter of the InN red quantum dot active layer 73 are set to be the largest, the band gap of the InN red quantum dot active layer 73 is reduced, the light-emitting intensity of the InN red quantum dot active layer 73 is improved, the defect of low intrinsic light-emitting intensity of the red quantum dot is further compensated, the light-emitting of the LED device is uniform, and the light-emitting efficiency of the device is 150lm / W-200lm / W.

[0037] Optionally, the thickness of the GaN barrier layer 712 of the InN blue quantum dot active layer 71 is 100nm, and the number of well-barrier cycles is 3-8; the thickness of the Al x Ga 1-x N / GaN barrier layer 722 is 120nm, the thickness ratio of the Al x Ga 1-x N and GaN is 1:3, and the number of well-barrier cycles is 2-5; the thickness of the Al y In z Ga 1-y- z N / Al w Ga 1-w N / GaN barrier layer 732 is 150nm, the thickness ratio of the Al y In z Ga 1-y-z N, Al w Ga 1-w N and GaN is 1:2:3, wherein 0.1<z≤0.5, y<z, 0.1≤w≤0.5, and the number of well-barrier cycles is 2-5.

[0038] Preferably, the InN blue quantum dot active layer 71 has a quantum dot diameter a = 5 nm, the first InN quantum dot well layer 711 has a thickness l = 20 nm, and the number of well-barrier cycles is 5; the InN green quantum dot active layer 72 has a quantum dot diameter b = 8 nm, the second InN quantum dot well layer 721 has a thickness m = 35 nm, the Al component is x = 0.1, and the number of well-barrier cycles is 3; the InN red quantum dot active layer 73 has a quantum dot diameter b = 8 nm, the third InN quantum dot well layer 731 has a thickness m = 35 nm, the Al component is y = 0.3 and w = 0.4, the In component is z = 0.3, and the number of well-barrier cycles is 3. The spectrum regulation effect of the quantum dot active layer 7 with the above parameter values is better, and the light-emitting efficiency of the device made therefrom can be up to 200 lm / W.

[0039] Optionally, the substrate 1 and the N-type semiconductor layer 5 are further provided with an AlN buffer layer 2, a three-dimensional nucleation layer 3, and a two-dimensional merging layer 4, the N-type semiconductor layer 5 and the quantum dot active layer 7 are further provided with a stress buffer layer 6, and the quantum dot active layer 7 and the P-type semiconductor layer 9 are further provided with a P-AlGaN layer 8, so as to form an epitaxial structure with complete functions and optimal performance.

[0040] The application further provides a preparation method of the LED epitaxial structure, comprising: providing a substrate 1, which can be any one of a Si substrate, a PSS sapphire substrate, and a SiC substrate, and using a metal organic chemical vapor deposition (MOCVD) method to sequentially deposit and grow, in a first direction, 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; wherein the quantum dot active layer 7 comprises, in the first direction, an InN blue quantum dot active layer 71, an InN green quantum dot active layer 72, and an InN red quantum dot active layer 73, which are sequentially grown.

[0041] Specifically, the InN blue quantum dot active layer 71 comprises at least one first InN quantum dot well layer 711 and a GaN barrier layer 712 which are alternately grown, the InN green quantum dot active layer 72 comprises at least one second InN quantum dot well layer 721 and an Al x Ga 1-x N / GaN barrier layer 722, and the InN red quantum dot active layer 73 comprises at least one third InN quantum dot well layer 731 and an Al y In z Ga 1-y-z N / Al w Ga 1-wN / GaN barrier layer 732, wherein 0.1≤x<y<w≤0.5, the potential barrier height of Al is used to adjust the distribution of carriers, to regulate the light intensity of different wavelengths, and to adjust the spectrum, thereby realizing the regulation of different spectra.

[0042] Optionally, the quantum dot diameters of the InN blue quantum dot active layer 71, the InN green quantum dot active layer 72, and the InN red quantum dot active layer 73 are a, b, and c, respectively, 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, respectively, and 2nm≤a<b<c≤15nm and 20nm≤l<m<n≤50nm, and the spectrum is further adjusted by regulating the InN quantum dot well layer thickness and the quantum dot diameter of each quantum dot active layer 7, so that the LED device emits light uniformly.

[0043] Optionally, the quantum dot active layer 7 is grown by alternately introducing TMIn and NH3 in a pulse growth mode, the growth pressure is 100Torr-300Torr, and the growth temperature is 500℃-650℃, and different quantum dot sizes and InN quantum dot well layer thicknesses are realized by different growth temperatures, V / III flux ratios (NH3 / TMIn flux ratios), and growth deposition times, the TMIn flow rate is 10sccm-100sccm, the NH3 flow rate is 500sccm-5000sccm, and the specific growth process of each quantum dot active layer is as follows: Growth of the InN blue quantum dot active layer 71: the growth temperature is 500℃-550℃, the NH3 and TMIn flux ratio is NH3 / TMIn≥200 (high V / III flux ratio), the flow rate of NH3 introduced is >2000sccm (N-rich condition), the growth deposition time is 10s-30s, the thickness of the GaN barrier layer 712 is 100nm, and the well / barrier cycle number is 3-8; Growth of the InN green quantum dot active layer 72: the growth temperature is 550℃-600℃, the NH3 and TMIn flux ratio is 50 x Ga 1-x The total thickness of the N / GaN barrier layer 722 is 120nm, the thickness ratio is 1:3, and the well / barrier cycle number is 2-5; Growth of the InN red quantum dot active layer 73: the growth temperature is 600℃-650℃, the NH3 and TMIn flux ratio is 10≤NH3 / TMIn<50 (low V / III flux ratio), the flow rate of NH3 introduced is >50sccm (In-rich condition), the growth deposition time is 50s-80s, the Al y In z Ga 1-y-z N / Alw Ga 1-w The total thickness of the N / GaN barrier layer 732 is 150 nm, and the thickness ratio is 1:2:3, and the number of well-barrier cycles is 1-3.

[0044] By the above different growth temperatures, flux ratios, and growth deposition times, the size and thickness are controlled to be 2 nm≤a<b<c≤15 nm and 20 nm≤l<m<n≤50 nm. Moreover, the application is in-situ growth of an epitaxial structure by MOCVD epitaxial deposition, which has a fast growth rate, low cost, and can be mass-produced. The size of the quantum dot and the thickness of the InN quantum dot well layer are convenient to adjust, and the control precision is high. The specific growth process of other epitaxial layers except the quantum dot active layer 7 is described below.

[0045] As Figure 4 shown, the preparation method and the effect of the core scheme of the present application are further illustrated by specific examples and comparative examples as follows: Comparative Example 1: Comparative Example 1 is a preparation method of a traditional LED epitaxial structure, and the active layer is a quantum well active layer 10 structure of InCaN well layer and CaN barrier layer superimposed, and a MOCVD device is used, and TMGa and TEGa are used as Ga sources, NH3 is used as a N source, TMIn is used as an In source, TMAl is used as an Al source, H2 and N2 are used as carrier gases, SiH4 and CP2Mg are used as N-type and P-type doping sources, a sapphire substrate is used, and a graphite disc is used as a substrate carrier disc for deposition growth, as shown in Figure 1 , and the preparation method specifically includes the following steps: S1, growing an AlN buffer layer 2 on a substrate: introducing H2 at a high temperature of 1150°C (temperature range: 900°C-1150°C) for 5 min of hydrogenation treatment to remove impurities, scratches, particles, etc. on the surface of the substrate, and then introducing TMAl, SiH4, NH3, H2, N2 at a high temperature of 1000°C (temperature range: 900°C-1150°C) to grow an AlN buffer layer 2 with a thickness of 25 nm (thickness range: 5 nm-50 nm), and the molar ratio of Si to Al is 0.2 (molar ratio range: 0.05-0.5).

[0046] S2, growing a three-dimensional nucleation layer 3 on the AlN buffer layer 2: introducing NH3, H2, N2 at a temperature of 900°C (temperature range: 800°C-1000°C), and the NH3 component is 20% (component range: 30%-80%), and the growth time is 1 min (time range: 0.5 min-3 min), and the lattice mismatch between GaN and AlN is used as a driving force to achieve a three-dimensional island growth mode in a small ammonia atmosphere by deposition decomposition.

[0047] S3, growing a two-dimensional merged layer 4 on the three-dimensional nucleation layer 3: introducing NH3, H2, N2, the temperature is 1100℃ (the temperature range is 900℃-1200℃), the NH3 component is 80% (the component range is 70%-100%), the growth time is 2min (the time range is 0.5min-3min), in a high-temperature and high-ammonia atmosphere, the three-dimensional island-shaped GaN plane is merged by using diffusion to realize a lateral growth mode, and the dislocation density is reduced.

[0048] S4, growing an N-type semiconductor layer 5 on the two-dimensional merged layer 4: the N-type semiconductor layer is an N-type gallium nitride layer, TMGa, SiH4, NH3, H2 and N2 are introduced, the growth thickness is 2000nm (the thickness range is 1500nm-2500nm), the growth temperature is 1050℃ (900℃-1200℃), the SiH4 doping concentration is 2E 18 / cm 3 .

[0049] S5, growing a stress buffer layer 6 on the N-type semiconductor layer 5: TEGa, TMIn, NH3, H2 and N2 are introduced, 30 (the cycle range is 25-35) cycles of InGaN / GaN superlattice structures are grown, the thickness of a single InGaN is 5nm, the thickness of a single GaN is 2nm, the total thickness of the stress buffer layer 6 is 210nm (the thickness range is 150nm-250nm), wherein the temperature of the InGaN well layer is 800℃ (the temperature range is 700℃-850℃), and the temperature of the GaN barrier layer is 880℃ (the temperature range is 800℃-1000℃).

[0050] S6, growing a quantum well active layer 10 on the stress buffer layer 6: TEGa, TMIn, SiH4, NH3, H2 and N2 are 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 10nm-16nm), wherein 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 cycles is 8 (the cycle range is 3-10).

[0051] S7, growing a P-AlGaN layer 8 on the quantum well active layer 10: TMAl, TMGa, CP2Mg, NH3 and H2 are introduced, the growth thickness is 200nm (the thickness range is 150nm-250nm), the growth pressure is 100 torr in an N2 atmosphere, the growth temperature is 900℃ (the temperature range is 850℃-1050℃), the growth rate is 20A / s, and the Mg doping concentration is 5E 19 / cm 3, the Al component x is 20% (component range: 0%~50%).

[0052] S8 growing a P-type semiconductor layer 9 on the P-AlGaN layer 8: the P-type semiconductor layer is a P-type gallium nitride layer, TMGa, CP2Mg, NH3, H2, N2 are input, the thickness is 400nm (thickness range: 200nm~600nm), the growth temperature is 1050℃ (temperature range: 800℃~1200℃), the Mg doping concentration is 1E 20 / cm 3 (the concentration range is 1E 19 / cm 3 -4E 20 / cm 3 ).

[0053] After the above steps are completed, a cooling annealing process is performed, and then the grown epitaxial wafer is tested. The photoelectric parameters are tested by EL, and the light-emitting efficiency of the device is 50lm / W-130lm / W. Therefore, the light-emitting efficiency of the traditional LED structure is low, the structure design is simple, the light emission is single, and if multiple wavelengths of light need to be emitted, multiple chips need to be mixed or matched with fluorescent light to synthesize, which has low conversion efficiency, complex packaging, and poor color rendering index.

[0054] Example 1: The active layer of Example 1 adopts a quantum dot active layer 7 structure. Except for the active layer, the growth process of other epitaxial layers is the same as that of Comparative Example 1. As shown in Figure 2 , the quantum dot active layer 7 of Example 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. The three quantum dot active layers are all periodic superpositions of InN quantum dot well layers and GaN barrier layers. The growth process is as follows: TEGa, TMIn, SiH4, NH3, H2, and N2 are input, the InN well region quantum dot temperature is 500℃-650℃, the barrier region growth temperature is 700℃-850℃, and the growth pressure is 100torr-300torr.

[0055] In Example 1, multiple wavelengths are emitted by a single chip by using quantum dot technology compared with Comparative Example 1. However, the well-barrier structure of each quantum dot active layer 7 is the same, and the barrier layer is GaN. The distribution of carriers cannot be adjusted by the potential barrier height of the barrier layer Al, and different growth temperatures, V / III flux ratios, and deposition times are not designed to obtain quantum dots of different sizes and InN quantum dot well layers of different thicknesses. Therefore, the spectrum cannot be adjusted, and the light-emitting efficiency of the device produced is 150lm / W, which is still relatively low and cannot meet market demand.

[0056] Example 2: The growth process of the quantum dot active layer 7 in this embodiment is different from that in Embodiment 1, and the growth process of other epitaxial layers is the same as that in Embodiment 1, as shown in Figure 3 In this embodiment, the barrier layer structure of each InN quantum dot active layer 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 arranged in a stack, the InN green light quantum dot active layer 72 includes at least one second InN quantum dot well layer 721 and an Al x Ga 1-x N / GaN barrier layer 722 grown alternately, and the InN red light quantum dot active layer 73 includes at least one third InN quantum dot well layer 731 and an Al y In z Ga 1-y-z N / Al w Ga 1-w N / GaN barrier layer 732, and different quantum dot sizes and well layer thicknesses are realized by different growth temperatures, flux ratios, and growth deposition times, and the growth process of the quantum dot active layer is as follows: In a pressure of 100 Torr~300 Torr, TMIn and NH3 are alternately input in a pulse growth mode, the well region quantum dot temperature is 500℃-650℃, the barrier region growth temperature is 700℃-850℃, the input flow rate of TMIn is 10sccm~100sccm, the input flow rate of NH3 is 500sccm~5000sccm, and the specific steps are as follows: First, grow the InN blue light quantum dot active layer 71: the growth temperature is 500℃-550℃, the V / III ratio flux ratio: NH3 / TMIn≥200, the input flow rate of NH3>2000sccm, the deposition time is 10s-30s, the quantum dot size is a=5nm, the thickness of the first InN quantum dot well layer 711 is l=20nm; the thickness of the GaN barrier layer 712 is 100nm, and the well-barrier period number is 5; Second, grow the InN green light quantum dot active layer 72: the growth temperature is 550℃-600℃, the V / III flux ratio: 50<NH3 / TMIn<200, the deposition time is 30s-50s, the quantum dot size is b=8nm, the thickness of the second InN quantum dot well layer 721 is m=35nm; the total thickness of the Al x Ga 1-x N / GaN barrier layer 722 is 120nm, the thickness ratio is 1:3, the Al component is x=0.1, and the well-barrier period number is 3; Finally, the growth of InN red quantum dot active layer 73: the growth temperature is 600-650℃, the V / III flux ratio is 10≤NH3 / TMIn<50, TMIn>50sccm, the deposition time is 50-80s; the quantum dot size is c=12nm, the thickness of the third InN quantum dot well layer 731 is n=50nm, the Al y In z Ga 1-y-z N / Al w Ga 1-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 well-barrier period number is 2.

[0057] In example 2, compared with example 1, different growth temperatures, V / III flux ratios and deposition times are designed to obtain quantum dots of different sizes and In quantum dot well layers of different thicknesses, so as to realize multi-wavelength light emission and spectral regulation; and the distribution of carriers is regulated by the Al barrier layer, so as to realize the regulation of the spectral proportion of different wavebands, achieve a suitable color temperature spectrum, and the spectral color temperature is adjustable. The light-emitting efficiency of the device prepared is tested to be as high as 200lm / W, the light-emitting efficiency is improved, and the market demand is met.

[0058] It is worth noting 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 only examples and do not represent the true thicknesses. Moreover, the true proportions between 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 as shown in the drawings, but are only for reference.

[0059] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0060] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An LED epitaxial structure, characterized in that: The invention comprises a substrate, and an N-type semiconductor layer, a quantum dot active layer, and a P-type semiconductor layer sequentially arranged in a first direction on the substrate; 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 sequentially arranged along the first direction, and the first direction is perpendicular to the substrate; The InN blue light quantum dot active layer includes at least one first InN quantum dot well layer and a GaN barrier layer arranged in a stacked manner, and the InN green light quantum dot active layer includes at least one second InN quantum dot well layer and an Al x Ga 1-x N / GaN barrier layer, and the InN red light quantum dot active layer includes at least one third InN quantum dot well layer and an Al y In z Ga 1-y-z N / Al w Ga 1-w N / GaN barrier layer, where 0.1 ≤ x < y < w ≤ 0.5, and the barrier height of Al is used to adjust the distribution of carriers.

2. The LED epitaxial structure according to claim 1, wherein: The quantum dot diameters of the InN blue quantum dot active layer, the InN green quantum dot active layer, and the InN red quantum dot active layer are a, b, and c, respectively, and 2nm≤a <b<c≤15nm。 3. The LED epitaxial structure according to claim 1, wherein: 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, respectively, and 20nm≤l <m<n≤50nm。 4. The LED epitaxial structure according to claim 1, wherein: The thickness of the GaN barrier layer of the InN blue - light quantum dot active layer is 100 nm, and the number of well - barrier periods is 3 - 8; the Al x Ga 1-x N / GaN barrier layer of the InN green - light quantum dot active layer has a thickness of 120 nm, and the thickness ratio of Al x Ga 1-x N to GaN is 1:3, and the number of well - barrier periods is 2 - 5; the Al y In z Ga 1-y-z [[ID=1,4]]N / Al w Ga 1-w N / GaN barrier layer of the InN red - light quantum dot active layer has a thickness of 150 nm, and the thickness ratio of Al[[ID=,19]] y In z Ga 1-y-z N, AlwGa 1-w N to GaN is 1:2:3, where 0.1 < z ≤ 0.5, y < z, 0.1 ≤ w ≤ 0.5, and the number of well - barrier periods is 2 - 5.

5. The LED epitaxial structure according to claim 1, wherein: An AlN buffer layer, a three-dimensional nucleation layer and a two-dimensional merging layer are provided between the substrate and the N-type semiconductor layer, a stress buffer layer is provided between the N-type semiconductor layer and the quantum dot active layer, and a P-AlGaN layer is provided between the quantum dot active layer and the P-type semiconductor layer.

6. A method for preparing an LED epitaxial structure, for preparing the LED epitaxial structure according to any one of claims 1 to 5, characterized in that: include: Providing a substrate, and using an MOCVD method to sequentially deposit and grow an N-type semiconductor layer, a quantum dot active layer, and a P-type semiconductor layer in a first direction on the substrate; The quantum dot active layer includes 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 sequentially grown along a first direction.

7. The method for preparing an LED epitaxial structure according to claim 6, wherein: The quantum dot active layer is grown by alternately introducing TMIn and NH3 in a pulsed growth mode, with a growth pressure of 100 Torr to 300 Torr and a growth temperature of 500° C. to 650° C., including end points.

8. The method for preparing an LED epitaxial structure according to claim 6, wherein: The growth temperature, NH3 / TMIn flux ratio and growth deposition time of the InN blue quantum dot active layer, InN green quantum dot active layer and InN red quantum dot active layer are all different, and the flow rate of TMIn is 10sccm~100sccm, and the flow rate of NH3 is 500sccm~5000sccm, including the end points.

9. The method for preparing an LED epitaxial structure according to claim 8, wherein: The growth temperature of the InN blue light quantum dot active layer is 500° C.-550° C., the flux ratio of NH3 and TMIn is: NH3 / TMIn≥200, the flow rate of NH3>2000 sccm, and the growth deposition time is 10s-30s, including the end values; The growth temperature of the InN green quantum dot active layer is 550° C.-600° C., the flux ratio of NH3 and TMIn is: 50<NH3 / TMIn<200, and the growth deposition time is 30s-50s, including the end values; The growth temperature of the InN red light quantum dot active layer is 600° C.-650° C., the flux ratio of NH3 and TMIn is: 10≤NH3 / TMIn<50, the flow rate of NH3 is>50sccm, and the growth deposition time is 50s-80s, including the end values.

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