LED epitaxial structure and preparation method thereof

Abstract

The application provides an LED epitaxial structure and a preparation method thereof. The LED epitaxial structure is prepared by adopting an MOCVD method. The epitaxial structure comprises 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 in sequence. 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 in sequence. The application sets multiple InN quantum dot active layers to realize multi-wavelength light emission, effectively suppresses density defects caused by a traditional structure, and adjusts a spectrum 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, intelligent and people-oriented lighting modes. 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 which is a superposition of an InCaN well layer and a CaN 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 In x Ga 1-x N material (x>0.4) and growth / device design, which includes the following aspects:

[0004] 1. Red light emission requires In component x>0.4 (corresponding to a band gap <2.0 eV), but high-In-content material growth is difficult, which is specifically embodied in that: high-In-content InCaN has a serious lattice mismatch with the GaN substrate, which will increase dislocations and significantly reduce light-emitting efficiency, and In atoms tend to aggregate in InGaN clusters, which will 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, "vacancy clusters" of In atom defects 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), forming In segregation (local In content >0.5) or three-dimensional island growth (instead of ideal two-dimensional layer growth), which further deteriorates the crystal quality.

[0005] 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.

[0006] 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.

[0007] 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

[0008] 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 inhibited, 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.

[0009] To achieve the above purpose, the solution of the present application is as follows:

[0010] An LED epitaxial structure is provided, 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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 thickness ratio of Al x Ga 1-x N and GaN is 1:3, the number of well-barrier periods 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 of the InN red quantum dot active layer is 150nm, and the thickness ratio of Al 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.

[0015] 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.

[0016] The application further provides a preparation method of the LED epitaxial structure, comprising:

[0017] A substrate is provided, and a N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer are sequentially deposited on the substrate in a first direction by using a MOCVD method.

[0018] 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.

[0019] 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 DEG C-650 DEG C, including the end point values.

[0020] 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, and the flow rate of TMIn input is 10 sccm-100 sccm, the flow rate of NH3 is 500 sccm-5000 sccm, including the end point values.

[0021] Optionally, the growth temperature of the InN blue quantum dot active layer is 500 DEG C-550 DEG C, the NH3 and TMIn flux ratio is NH3 / TMIn≥200, the input flow rate of NH3 is >2000 sccm, and the growth deposition time is 10 s-30 s, including the end point values.

[0022] The growth temperature of the InN green quantum dot active layer is 550 DEG C-600 DEG C, the NH3 and TMIn flux ratio is 50

[0023] The growth temperature of the InN red quantum dot active layer is 600 DEG C-650 DEG C, the NH3 and TMIn flux ratio is 10≤NH3 / TMIn<50, the input flow rate of NH3 is >50 sccm, and the growth deposition time is 50 s-80 s, including the end point values.

[0024] After the above scheme is used, the application has the following advantages:

[0025] 1. The application uses an InN quantum dot active layer structure to realize single LED chip multi-wavelength light emission, and the structure is simple.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 5、The application also adjusts the spectrum by controlling different sizes of quantum dots and 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 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 light quantum dot active layer are set to be the largest, 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.

[0030] 6、The diameter of the quantum dot is controlled to be greater than or equal to 2nm, so that the surface ratio is not too high due to too small size, the defect state density is not too high, the energy level dispersion is not too large, and the carrier localization is not out of control; the diameter is controlled to be less than or equal to 15nm, so that the quantum confinement effect disappears due to too large size, the band gap cannot be adjusted, the carrier localization is weakened, and the Auger recombination rate is not increased.

[0031] 7、The InN quantum dot well layer thickness of each quantum dot active layer is controlled to be greater than or equal to 20nm, so that the carrier is not diffused out of the active layer when the carrier is not recombined, the carrier is fully captured and recombined, and quantum tunneling leakage is avoided; the thickness is controlled to be less than or equal to 50nm, so that the carrier transport path is too long due to too thick, the probability of being captured by defects is increased, non-radiative recombination loss and stress accumulation can be suppressed, and high crystal quality is maintained. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is an epitaxial structure schematic diagram of the present application comparative example 1;

[0033] Figure 2 It is an epitaxial structure schematic diagram of the present application comparative example 1;

[0034] Figure 3 It is a structure schematic diagram of the quantum dot active layer of the present application comparative example 2;

[0035] Figure 4 It is a preparation method flow chart of the present application.

[0036] REFERENCE NUMERALS:

[0037] 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-xN / GaN barrier layer; 73, InN red quantum dot active layer; 731, third InN quantum dot well layer; 732, Al y In z Ga 1-y-z N / 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

[0038] 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 a person of ordinary skill in the art without creative work fall within the scope of protection of the present application, and the range of the present application includes two end values.

[0039] As Figures 1-2 shown, the present application provides an LED epitaxial structure, comprising a substrate 1, and an N-type semiconductor layer 5, a quantum dot active layer 7, and a P-type semiconductor layer 9 arranged in a first direction on the substrate in sequence, the first direction being 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 quantum dot active layer 71, an InN green quantum dot active layer 72, and an InN red quantum dot active layer 73 arranged in the first direction in sequence.

[0040] Quantum dots (QDs) are a kind of nanoscale semiconductor functional materials, and their unique three-dimensional confined structure can effectively suppress or alleviate density defects (such as point defects, dislocations, and lattice distortions) in the material through multiple mechanisms, thereby improving optical and electrical properties. Density defects generally refer to local disordered regions in which atoms / molecules deviate from the ideal lattice structure, and common types include point defects, dislocations, and lattice distortions. The present application uses quantum dot structures as active layers, which suppresses the density defects of traditional LED active layers through four mechanisms of quantum confinement reconfiguration of energy levels, surface passivation to eliminate dangling bonds, heterojunction isolation of defect effects, and optimization of growth kinetics.

[0041] In addition, the present application uses InN quantum dots as active layer structures, which completely eliminates problems such as clusters, segregation, and broadening of the emission peak caused by In / Ga phase separation, and the mismatch degree between InN and GaN substrate is low, which slows down dislocation defects, the growth temperature of InN quantum dots is also lower than that of traditional InGaN, which suppresses the desorption of In and improves the incorporation of In.

[0042] Optionally, the emission wavelengths 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 420nm-480nm, 500nm-560nm, and 580nm-640nm, respectively. The shorter the emission wavelength, the higher the intrinsic luminous intensity. The InN blue quantum dot active layer 71 has the highest intrinsic luminous intensity, and the InN red quantum dot active layer 73 has the lowest intrinsic luminous intensity. This application controls the spectrum by controlling the Al composition, the thickness of the InN quantum dot well layer, and the size of the quantum dots to improve the luminous intensity of the InN red quantum dot active layer 73 and make the light emission of the LED device uniform.

[0043] 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 layer, resulting in limited effect on spectrum adjustment and low device luminous efficiency.

[0044] like Figure 3 As shown, in a preferred embodiment, the InN blue quantum dot active layer 71 includes at least one first InN quantum dot well layer 711 and a GaN barrier layer 712 stacked together; the InN green quantum dot active layer 72 includes at least one second InN quantum dot well layer 721 and an Al2O3 barrier layer 712 stacked together. x Ga 1-x N / GaN barrier layer 722; the InN red quantum dot active layer 73 includes at least one third InN quantum dot well layer 731 and Al stacked together. y In z Ga 1-y-z N / Al w Ga 1-w N / GaN barrier layer 732, where 0.1≤x <y<w≤0.5。

[0045] The InN blue quantum dot active layer 71 uses a pure GaN barrier layer, which avoids the introduction of unnecessary barriers by Al. Moreover, the InN quantum dots and GaN barriers form Type-II band alignment, with holes localized within the quantum dots and electrons distributed in the barrier region. This can weaken the built-in polarization field, improve radiative recombination efficiency, and enhance luminescence efficiency.

[0046] The InN green quantum dot active layer 72 uses an AlGaN / GaN composite barrier layer with low Al content to balance the charge carriers, while the InN red quantum dot active layer 73 uses an AlInGaN / AlGaN / GaN composite barrier layer structure. Its Al content is higher than that of the InN green quantum dot active layer 72, forming a high electronic barrier, resulting in high electron utilization and improved luminous intensity. This compensates for the defect of low intrinsic luminous intensity of red quantum dots and makes the luminous emission of the LED device uniform.

[0047] 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 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.

[0048] 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 barrier layer 722 of the InN green quantum dot active layer 72 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 of the InN red quantum dot active layer 73 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.

[0049] 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 as high as 200 lm / W.

[0050] 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.

[0051] The application further provides a preparation method of the LED epitaxial structure, comprising:

[0052] The substrate 1 can be any one of a Si substrate, a PSS sapphire substrate, and a SiC substrate. An MOCVD method is used 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. 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.

[0053] 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 height of the barrier layer of Al is used to adjust the distribution of carriers, to regulate the light intensity of different wavelengths, to adjust the spectrum, and to realize the regulation of different spectra.

[0054] 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, so that 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, and the LED device emits light uniformly.

[0055] Optionally, the quantum dot active layer 7 is grown by alternately inputting TMIn and NH3 in a pulse growth mode, the growth pressure is 100Torr-300Torr, 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 processes of each quantum dot active layer are as follows:

[0056] The InN blue quantum dot active layer 71 is grown at a growth temperature of 500℃-550℃, an NH3 and TMIn flux ratio of NH3 / TMIn≥200 (high V / III flux ratio), an input flow rate of NH3>2000sccm (N-rich condition), a growth deposition time of 10s-30s, a thickness of the GaN barrier layer 712 of 100nm, and a well / barrier cycle number of 3-8;

[0057] The InN green quantum dot active layer 72 is grown at a growth temperature of 550℃-600℃, an NH3 and TMIn flux ratio of 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;

[0058] The InN red quantum dot active layer 73 is grown at a growth temperature of 600℃-650℃, an NH3 and TMIn flux ratio of 10≤NH3 / TMIn<50 (low V / III flux ratio), an input flow rate of NH3>50sccm (In-rich condition), a growth deposition time of 50s-80s, and an Aly In z Ga 1-y-z N / Al w Ga 1-w The total thickness of the N / GaN barrier layer 732 is 150 nm, the thickness ratio is 1:2:3, and the number of well-barrier cycles is 1-3.

[0059] By the above different growth temperatures, flux ratios, and growth deposition times, the size and thickness control of 2 nm≤a<b<c≤15 nm and 20 nm≤l<m<n≤50 nm is achieved. Moreover, the present application is in-situ grown by MOCVD epitaxial deposition, 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.

[0060] 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:

[0061] Comparative Example 1:

[0062] Comparative Example 1 is a preparation method of a traditional LED epitaxial structure, the active layer of which is a quantum well active layer 10 structure of InCaN well layer and CaN barrier layer superimposed, and the MOCVD equipment is used, TMGa and TEGa are used as Ga sources, NH3 is used as N source, TMIn is used as In source, TMAl is used as Al source, H2 and N2 are used as carrier gas, 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 , the preparation method specifically includes the following steps:

[0063] S1, growing an AlN buffer layer 2 on a substrate: hydrogenating at a high temperature of 1150°C (temperature range of 900°C-1150°C) for 5 min by passing H2 to remove impurities, scratches, particles, etc. on the surface of the substrate, and then growing an AlN buffer layer 2 by passing TMAl, SiH4, NH3, H2, and N2 at a high temperature of 1000°C (temperature range of 900°C-1150°C), with a thickness of 25 nm (thickness range of 5 nm-50 nm) and a molar ratio of Si to Al of 0.2 (molar ratio range of 0.05-0.5).

[0064] S2, growing a three-dimensional nucleation layer 3 on the AlN buffer layer 2: introducing NH3, H2, N2, the temperature is 900℃ (the temperature range is 800℃-1000℃), the NH3 component is 20% (the component range is 30%-80%), the growth time is 1min (the time range is 0.5min-3min), taking the lattice mismatch between GaN and AlN as the driving force, and using deposition decomposition to realize a three-dimensional island growth mode in a small ammonia atmosphere.

[0065] S3, growing a two-dimensional merging 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), using diffusion to realize a lateral growth mode in a high-temperature large-ammonia atmosphere, and merging the three-dimensional islands into a GaN plane to reduce the dislocation density.

[0066] S4, growing an N-type semiconductor layer 5 on the two-dimensional merging layer 4: the N-type semiconductor layer is an N-type gallium nitride layer, introducing TMGa, SiH4, NH3, H2, N2, 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 .

[0067] S5, growing a stress buffer layer 6 on the N-type semiconductor layer 5: introducing TEGa, TMIn, NH3, H2, N2, growing an InGaN / GaN superlattice structure with 30 cycles (the cycle range is 25-35), 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℃).

[0068] S6, growing a quantum well active layer 10 on the stress buffer layer 6: introducing TEGa, TMIn, SiH4, NH3, H2, N2, 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).

[0069] S7, growing a P-AlGaN layer 8 on the quantum well active layer 10: TMAl, TMGa, CP2Mg, NH3, H2 are introduced, the thickness is 200 nm (the thickness ranges from 150 nm to 250 nm), the growth pressure is 100 torr under the atmosphere of N2, the growth temperature is 900℃ (the temperature ranges from 850℃ to 1050℃), the growth rate is 20 A / s, and the doping concentration of Mg is 5E 19 / cm 3 , and the Al component x is 20% (the component ranges from 0% to 50%).

[0070] 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, and N2 are introduced, the thickness is 400 nm (the thickness ranges from 200 nm to 600 nm), the growth temperature is 1050℃ (the temperature ranges from 800℃ to 1200℃), and the doping concentration of Mg is 1E 20 / cm 3 (the concentration ranges from 1E 19 / cm 3 to 4E 20 / cm 3 ).

[0071] 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 50 lm / W-130 lm / 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.

[0072] Example 1:

[0073] The active layer of Example 1 adopts a quantum dot active layer 7 structure. Except for the active layer, the growth process of the 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 introduced, the InN well region quantum dot temperature is 500℃-650℃, the barrier region growth temperature is 700℃-850℃, and the growth pressure is 100 torr-300 torr.

[0074] In the embodiment 1, the single chip emits multiple wavelengths by using quantum dot technology, but the well barrier structure of each quantum dot active layer 7 is the same, and the barrier layer is GaN, which cannot adjust the distribution of carriers by the barrier height of Al, and different growth temperatures, V / III flux ratio and deposition time are not designed to obtain quantum dots of different size and InN quantum dot well layer thickness, which cannot control the spectrum, and the light emitting efficiency of the device is tested to be 150 lm / W, which is relatively low and cannot meet the market demand.

[0075] Embodiment 2

[0076] 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 The barrier layer structure of each InN quantum dot active layer in this embodiment is different, the InN blue quantum dot active layer 71 includes at least one first InN quantum dot well layer 711 and GaN barrier layer 712 stacked, the InN green quantum dot active layer 72 includes at least one second InN quantum dot well layer 721 and Al x Ga 1-x N / GaN barrier layer 722 alternately grown, and the InN red quantum dot active layer 73 includes at least one third InN quantum dot well layer 731 and 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:

[0077] In the pressure of 100 Torr~300 Torr, TMIn and NH3 are alternately input in pulse growth mode, the well region quantum dot temperature is 500℃-650℃, the barrier region growth temperature is 700℃-850℃, the input flow of TMIn is 10sccm~100sccm, the input flow of NH3 is 500sccm~5000sccm, and the specific steps are as follows:

[0078] First, grow the InN blue quantum dot active layer 71: the growth temperature is 500℃-550℃, the V / III ratio flux ratio: NH3 / TMIn≥200, the input flow 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;

[0079] Secondly, growing InN green quantum dot active layer 72: growth temperature is 550-600℃, V / III flux ratio: 50<NH3 / TMIn<200, deposition time is 30-50s, quantum dot size is b=8nm, thickness of second InN quantum dot well layer 721 is m=35nm; Al x Ga 1-x N / GaN barrier layer 722 total thickness is 120nm, thickness ratio is 1:3, Al component is x=0.1, well-barrier cycle number is 3;

[0080] Finally, growing InN red quantum dot active layer 73: growth temperature is 600-650℃, V / III flux ratio: 10<NH3 / TMIn<50, TMIn>50sccm, deposition time is 50-80s; quantum dot size is c=12nm, thickness of third InN quantum dot well layer 731 is n=50nm, Al y In z Ga 1-y-z N / Al w Ga 1-w N / GaN barrier layer 732 total thickness is 150nm, thickness ratio is 1:2:3, Al component is y=0.3, z=0.4, y<z, In component is w=0.3, well-barrier cycle number is 2.

[0081] 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, to realize multi-wavelength light emission and spectrum regulation; and Al barrier layers are used to block electrons to regulate the distribution of carriers, so as to realize regulation of the spectrum proportion of different wavebands, achieve a suitable color temperature spectrum, and the spectrum and color temperature are adjustable; the light-emitting efficiency of the prepared device is tested to be as high as 200lm / W, the light-emitting efficiency is improved, and the market demand is met.

[0082] 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.

[0083] The various embodiments described in this specification are intended to be illustrative only and in no way limit the scope of the application. Changes and modifications can be made to these embodiments without departing from the spirit or scope of the application. Accordingly, the specification is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present application.

[0084] The above description of disclosed embodiments is intended to be illustrative only and not limiting of the scope of the application. Many modifications of the embodiments described herein will be readily apparent to those skilled in the art and the general principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Accordingly, the specification is to be regarded as illustrative only and not restrictive of the scope of the present application.

Claims

1. An LED epitaxial structure, characterized in that: The application relates to a quantum dot light emitting diode, which comprises a substrate, and an N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer arranged in sequence 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 sequence in the first direction, and the first direction is perpendicular to the substrate. The InN blue quantum dot active layer comprises at least one first InN quantum dot well layer and GaN barrier layer arranged in a stack, the InN green quantum dot active layer comprises at least one second InN quantum dot well layer and Al x Ga 1-x N / GaN barrier layer arranged in a stack, and the InN red quantum dot active layer comprises at least one 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 arranged in a stack, wherein 0.1<=x<y<w<=0.5, 0.1<=z<=0.5, y<z, and the distribution of carriers is adjusted by the barrier height of Al. 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 2nm<=a<b<c<=15nm. 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 20nm<=l<m<n<=50nm.

2. An LED epitaxial structure as claimed in claim 1, wherein: The thickness of the GaN barrier layer of the InN blue quantum dot active layer is 100 nm, and the number of well-barrier periods is 3-8; the thickness of the Al x Ga 1-x N / GaN barrier layer is 120 nm, and the thickness ratio of Al x Ga 1-x N and GaN is 1:3, and the number of well-barrier periods 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 is 150 nm, and the thickness ratio of Al y In z Ga 1-y-z N, AlwGa 1-w N and GaN is 1:2:3, and the number of well-barrier periods is 2-5.

3. An LED epitaxial structure as claimed in claim 1, wherein: 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.

4. A method for producing an LED epitaxial structure as claimed in any one of claims 1 to 3, characterized in that The application relates to a quantum dot light emitting diode, which comprises a substrate, and an N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer arranged in sequence 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 sequence in the first direction, and the first direction is perpendicular to the substrate. The application relates to a quantum dot light emitting diode, which comprises a substrate, and an N-type semiconductor layer, a quantum dot active layer and a P-type semiconductor layer arranged in sequence 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 sequence in the first direction, and the first direction is perpendicular to the substrate. The quantum dot active layer is alternately grown by pulse growth mode by inputting TMIn and NH3, the growth pressure is 100Torr-300Torr, the growth temperature is 500 DEG C-650 DEG C, and the end point values are included.

5. The method for preparing an LED epitaxial structure as described in claim 4, characterized in that: The growth temperature, the NH3 / 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 different, the flow rate of inputted TMIn is 10sccm-100sccm, the flow rate of inputted NH3 is 500sccm-5000sccm, and the end point values are included.

6. The method of claim 4, wherein: The growth temperature of the InN blue light quantum dot active layer is 500 DEG C-550 DEG C, the NH3 and TMIn flux ratio is NH3 / TMIn>=200, the input flow rate of NH3 is >2000sccm, and the growth deposition time is 10s-30s, and the end point values are included.

7. The method of claim 6, wherein: The growth temperature of the InN green light quantum dot active layer is 550 DEG C-600 DEG C, the NH3 and TMIn flux ratio is 50<NH3 / TMIn<200, the growth deposition time is 30s-50s, and the end point values are included. The growth temperature of the InN red light quantum dot active layer is 600 DEG C-650 DEG C, the NH3 and TMIn flux ratio is 10<=NH3 / TMIn<50, the input flow rate of NH3 is >50sccm, the growth deposition time is 50s-80s, and the end point values are included. ​

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