Gallium nitride-based LED epitaxial structure and preparation method thereof

Abstract

The application provides a gallium nitride LED epitaxial structure and a preparation method thereof. The active layer comprises a first composite region, a stress transition layer and a second composite region arranged in sequence along a first direction. The In component of the stress transition layer is arranged to realize stress transition between the InGaN / GaN superlattice structure (i.e. the first composite region) and the main light-emitting region (i.e. the second composite region), so as to avoid the polarization effect of the InGaN / GaN superlattice structure caused by the lattice mismatch of the two materials from affecting the main light-emitting region. Meanwhile, the material and thickness of the stress transition layer are arranged to be equivalent to the front quantum well, so as to capture the carrier leaked through the penetrating dislocation center in the V-shaped pit and make the carrier radiate and recombine, thereby improving the internal quantum efficiency of the active layer and enhancing the brightness of the LED chip.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of light emitting diode, in particular to a gallium nitride LED epitaxial structure and a preparation method thereof. BACKGROUND

[0002] At present, GaN-based LED light-emitting materials play an increasingly more application in display, lighting, biotechnology, sensors and other fields due to their physical and chemical properties such as wide band gap, high breakdown electric field, high electron saturation mobility, etc. The active region of GaN-based LED is mostly InGaN / GaN. Due to the lattice mismatch between GaN and InGaN materials, polarization effect is generated, which causes the discontinuity of conduction band and valence band, thereby causing the phenomenon that the internal quantum efficiency of the light-emitting device deteriorates with the increase of the applied current density. Moreover, due to the large difference in the migration rate of electrons and holes, electrons are prone to overflow to the P-type semiconductor layer, while the hole migration rate is low and prone to non-radiative recombination in the P-type semiconductor layer, which further reduces the light-emitting efficiency of the LED. Therefore, reducing electron leakage, increasing hole injection efficiency, weakening strong polarization electric field, and promoting efficient recombination of carriers in the active region have become urgent problems to be solved to improve the light-emitting power of the LED.

[0003] At present, the following designs are adopted in the InGaN / GaN active region: such as setting the In component of InGaN / GaN constant, the quantum barrier (QB) thickness constant, setting high Al component AlGaN as an electron blocking layer between the active region and the P-type semiconductor layer, etc.

[0004] When the In component of the InGaN / GaN active region is constant and the quantum barrier (QB) thickness is constant, the lattice mismatch is large, the polarization electric field is strong, and the crystal quality of the high In component InGaN material is worse, which affects the light-emitting efficiency of the LED.

[0005] After the InGaN quantum well layer is grown, AlGaN material is grown as an electron blocking layer. Due to the difference in lattice constant, the dislocation density of the AlGaN layer is further increased, which causes defects in the AlGaN material and easily captures electrons and holes, reduces the radiation recombination efficiency, and further reduces the internal quantum efficiency of the LED. Moreover, the problems of the difference in lattice constant between the AlGaN material and the GaN material and the low migration rate of Al atoms on the epitaxial surface cause many defects in the subsequent growth of the P-type semiconductor layer material, which reduces the activation efficiency of the holes and further reduces the internal quantum efficiency of the LED, and finally affects the light-emitting efficiency of the epitaxial wafer.

[0006] Therefore, the present inventors specially design a gallium nitride LED epitaxial structure and a preparation method thereof, and the present case is generated. SUMMARY

[0007] The application aims to provide a gallium nitride LED epitaxial structure and a preparation method thereof, and solve the problem of low light-emitting efficiency of LED chips.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0009] A gallium nitride LED epitaxial structure comprises:

[0010] A substrate and an N-type semiconductor layer, an active layer and a P-type semiconductor layer which are sequentially stacked on the surface of the substrate; the active layer comprises a first composite region, a stress transition layer and a second composite region which are sequentially arranged along a first direction;

[0011] The first composite region comprises an InGaN / GaN superlattice structure which can form a V-shaped pit.

[0012] The stress transition layer comprises an InGaN material layer, and the stress transition layer and the InGaN / GaN superlattice structure have the same In component.

[0013] The second composite region comprises a plurality of quantum well period structures which are sequentially arranged along the first direction, wherein each quantum well period structure comprises alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer is at least consistent with the thickness of the quantum well layer in the quantum well period structure adjacent to the stress transition layer; the first direction is perpendicular to the substrate and is directed from the substrate to the N-type semiconductor layer.

[0014] Preferably, in the second composite region, the thickness of the quantum well layer in the last quantum well period structure along the first direction is smaller than the thickness of the quantum well layer in any other quantum well period structure.

[0015] Preferably, in the second composite region, the growth rate of the quantum barrier layer in the last quantum well period structure along the first direction is smaller than the growth rate of the quantum barrier layer in any other quantum well period structure.

[0016] Preferably, in the second composite region, the growth temperature of the quantum barrier layer in the last quantum well period structure along the first direction is higher than the growth temperature of the quantum barrier layer in any other quantum well period structure.

[0017] Preferably, in the second composite region, the first quantum well period structure along the first direction comprises alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; and the last quantum well period structure along the first direction comprises alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

[0018] Preferably, in the second recombination region, the growth rate of the quantum barrier layers corresponding to the quantum well periodic structures along the first direction gradually decreases.

[0019] Preferably, in the second recombination region, the growth temperature of the quantum barrier layers corresponding to the quantum well periodic structures along the first direction gradually increases.

[0020] Preferably, the second recombination region includes three quantum well periodic structures arranged in sequence along the first direction, namely the first quantum well periodic structure, the second quantum well periodic structure and the third quantum well periodic structure; then the thickness of the stress transition layer is at least the same as the thickness of the quantum well layer in the first quantum well periodic structure.

[0021] Preferably, the thickness of the stress transition layer is consistent with the thickness of the quantum well layer in the second quantum well periodic structure.

[0022] Preferably, the first quantum well periodic structure includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; the second quantum well periodic structure includes alternately stacked GaN quantum barrier layers and InGaN quantum well layers; and the third quantum well periodic structure includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

[0023] The present invention also provides a method for preparing a gallium nitride-based LED epitaxial structure, comprising:

[0024] providing a substrate;

[0025] An N-type semiconductor layer, an active layer, and a P-type semiconductor layer are sequentially grown on the surface of the substrate; the active layer comprises a first recombination region, a stress transition layer, and a second recombination region sequentially arranged along a first direction;

[0026] wherein the first recombination region comprises an InGaN / GaN superlattice structure capable of forming a V-shaped pit;

[0027] The stress transition layer includes an InGaN material layer, and the stress transition layer and the InGaN / GaN superlattice structure have the same In composition;

[0028] The second recombination region includes a plurality of quantum well periodic structures sequentially arranged along the first direction, wherein each of the quantum well periodic structures includes alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer is at least consistent with the thickness of the quantum well layer in the quantum well periodic structure adjacent thereto.

[0029] Preferably, in the second composite region, the quantum well layer in the last quantum well period structure along the first direction has a thickness smaller than that in any other quantum well period structure.

[0030] Preferably, in the second composite region, the first quantum well period structure along the first direction comprises alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; and the last quantum well period structure along the first direction comprises alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

[0031] Preferably, in the second composite region, the growth rate of the quantum barrier layer in the last quantum well period structure along the first direction is smaller than that in any other quantum well period structure by adjusting the flow rate of Ga source.

[0032] Preferably, in the second composite region, the growth temperature of the quantum barrier layer corresponding to each quantum well period structure along the first direction gradually increases.

[0033] Preferably, in the InGaN / GaN superlattice structure, the V-shaped pits are formed by using the growth rate difference of Ga atoms in different directions at the same temperature.

[0034] According to the technical solution, the GaN-based LED epitaxial structure comprises a first composite region, a stress transition layer and a second composite region arranged in sequence along a first direction; the first composite region comprises an InGaN / GaN superlattice structure capable of forming V-shaped pits; the stress transition layer comprises an InGaN material layer, and the stress transition layer and the InGaN / GaN superlattice structure have the same In component; the second composite region comprises a plurality of quantum well period structures arranged in sequence along the first direction, each of the quantum well period structures comprises alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer is at least consistent with the thickness of the quantum well layer in the quantum well period structure adjacent to the stress transition layer. Thus, by adjusting the In component of the stress transition layer, the stress transition between the InGaN / GaN superlattice structure (i.e., the first composite region) and the main light-emitting region (i.e., the second composite region) is realized, and the polarization effect caused by the lattice mismatch between the two materials in the InGaN / GaN superlattice structure is avoided from affecting the main light-emitting region; meanwhile, by adjusting the material and thickness of the stress transition layer, the stress transition layer is equivalent to the front quantum well, so as to capture the carrier leaked through the penetrating dislocation center in the V-shaped pit and make the carrier radiate and recombine, thereby improving the internal quantum efficiency of the active layer and enhancing the brightness of the LED chip.

[0035] Secondly, by setting in the second recombination region, the thickness of the quantum well layer in the last quantum well period structure along the first direction is less than the thickness of the quantum well layer in any other quantum well period structure. Based on this, the narrow well design of the last quantum well period structure is realized, which is beneficial to the realization of the electron-hole wave function overlap in the remaining quantum well period structure to improve the radiation recombination probability in this region, thereby avoiding the concentration of the recombination of most carriers in the last quantum well period structure due to the imbalance of hole and electron injection.

[0036] Then, by setting in the second recombination region, the growth rate of the quantum barrier layer in the last quantum well period structure along the first direction is less than the growth rate of the quantum barrier layer in any other quantum well period structure. Based on this, the quantum barrier layer in the last quantum well period structure grows at the slowest rate, which can further release stress, reduce stress accumulation and weaken the polarization field, thereby increasing the radiation recombination of the active region to better improve the light-emitting efficiency of the LED.

[0037] Next, by setting in the second recombination region, the growth temperature of the quantum barrier layer in the last quantum well period structure along the first direction is higher than the growth temperature of the quantum barrier layer in any other quantum well period structure. Based on this, by growing the quantum barrier layer close to the main light-emitting region at a high temperature, the crystal defects are reduced, thereby obtaining the best crystal quality.

[0038] Finally, by setting in the second recombination region, the first quantum well period structure along the first direction includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; the last quantum well period structure along the first direction includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers. Based on this, the quantum barrier layer of the first quantum well period structure is designed as an AlGaN layer, thereby improving the barrier height by doping Al, which can slow down electron migration; and the quantum barrier layer in the last quantum well period structure is designed as an InGaN layer, which can reduce the lattice mismatch with the narrow well on the one hand, thereby weakening the strong polarization field formed due to the lattice mismatch; on the other hand, the InGaN quantum barrier layer has a lower barrier height, which is beneficial to hole injection; therefore, the recombination of electrons and holes can be further enhanced, thereby improving the light-emitting efficiency.

[0039] The application also provides a preparation method of a gallium nitride-based LED epitaxial structure, which is simple in operation and easy to implement while achieving the above technical effects. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to make the technical solutions of the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only need to explain the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative effort based on the provided drawings.

[0041] Figure 1 Structure schematic diagram of the gallium nitride LED epitaxial structure provided by the embodiment of the present application;

[0042] Figure 2 Structure schematic diagram of the second composite region provided by the embodiment of the present application;

[0043] Figure 3 Structure schematic diagram of the first composite region provided by the embodiment of the present application;

[0044] Figure 4 Growth control mode schematic diagram of the second composite region provided by the embodiment of the present application;

[0045] Figure 5 Structure schematic diagram of the first quantum well periodic structure provided by the embodiment of the present application;

[0046] Figure 6 Structure schematic diagram of the second quantum well periodic structure provided by the embodiment of the present application;

[0047] Figure 7 Structure schematic diagram of the third quantum well periodic structure provided by the embodiment of the present application;

[0048] Explanation of symbols in the drawings:

[0049] 1, substrate,

[0050] 2, buffer layer,

[0051] 3, N-type semiconductor layer;

[0052] 4, first composite region;

[0053] 5, stress transition layer;

[0054] 6, second composite region, 6.1, 6.2, …, 6.n: nth quantum well periodic structure

[0055] 7, P-type semiconductor layer. DETAILED DESCRIPTION

[0056] To make the content of the present invention clearer, the content of the present invention is further described below with reference to the accompanying drawings. The present invention is not limited to the specific embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0057] like Figure 1 As shown, a GaN-based LED epitaxial structure includes:

[0058] A substrate 1 and an N-type semiconductor layer 3, an active layer, and a P-type semiconductor layer 7 sequentially stacked on the surface of the substrate 1; the active layer includes a first recombination region 4, a stress transition layer 5, and a second recombination region 6 sequentially arranged along a first direction;

[0059] Wherein, the first recombination region 4 comprises an InGaN / GaN superlattice structure capable of forming a V-shaped pit;

[0060] The stress transition layer 5 comprises an InGaN material layer, and the stress transition layer 5 and the InGaN / GaN superlattice structure have the same In composition;

[0061] like Figure 2 As shown, the second recombination region 6 includes a plurality of quantum well periodic structures (6.1, 6.2...6.n) arranged in sequence along the first direction, wherein each of the quantum well periodic structures includes alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer 5 is at least consistent with the thickness of the quantum well layer in the quantum well periodic structure adjacent thereto; the first direction is perpendicular to the substrate 1 and points from the substrate 1 to the N-type semiconductor layer 3.

[0062] It is worth noting that the type of substrate 1 is not limited in this embodiment. For example, substrate 1 includes any one of sapphire, silicon carbide, silicon, gallium nitride, and aluminum nitride. Furthermore, the types of N-type semiconductor layer 3 and P-type semiconductor layer 7 are also not limited. For example, N-type semiconductor layer 3 can be, but is not limited to, a gallium nitride layer, and correspondingly, P-type semiconductor layer 7 can be, but is not limited to, a gallium nitride layer.

[0063] In addition, a buffer layer 2 is provided between the substrate 1 and the N-type semiconductor layer 3 .

[0064] Furthermore, based on the above embodiment of the present invention, in the second recombination region 6 , the thickness of the quantum well layer in the last quantum well periodic structure along the first direction is smaller than the thickness of the quantum well layer in any other quantum well periodic structure.

[0065] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth rate of the quantum barrier layer in the last quantum well periodical structure along the first direction is less than the growth rate of the quantum barrier layer in any other quantum well periodical structure.

[0066] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth temperature of the quantum barrier layer in the last quantum well periodical structure along the first direction is higher than the growth temperature of the quantum barrier layer in any other quantum well periodical structure.

[0067] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the first quantum well periodical structure along the first direction comprises AlGaN quantum barrier layers and InGaN quantum well layers which are alternately stacked; and the last quantum well periodical structure along the first direction comprises InGaN quantum barrier layers and InGaN quantum well layers which are alternately stacked.

[0068] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth rate of the quantum barrier layer corresponding to each quantum well periodical structure along the first direction gradually decreases.

[0069] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth temperature of the quantum barrier layer corresponding to each quantum well periodical structure along the first direction gradually increases.

[0070] Further, based on the above-mentioned embodiments of the present application, as a preferred embodiment of the present application, the second composite region 6 comprises three quantum well periodical structures arranged along the first direction in sequence, which are the first quantum well periodical structure, the second quantum well periodical structure and the third quantum well periodical structure; and the thickness of the stress transition layer 5 is at least the same as the thickness of the quantum well layer in the first quantum well periodical structure.

[0071] Further, based on the above-mentioned embodiments of the present application, the thickness of the stress transition layer 5 is the same as the thickness of the quantum well layer in the second quantum well periodical structure.

[0072] Further, based on the above-mentioned embodiments of the present application, the first quantum well periodical structure comprises AlGaN quantum barrier layers and InGaN quantum well layers which are alternately stacked; the second quantum well periodical structure comprises GaN quantum barrier layers and InGaN quantum well layers which are alternately stacked; and the third quantum well periodical structure comprises InGaN quantum barrier layers and InGaN quantum well layers which are alternately stacked. Further, a Cap layer for protecting the quantum well is arranged behind the quantum well layer in each quantum well periodical structure (the first quantum well periodical structure, the second quantum well periodical structure and the third quantum well periodical structure).

[0073] The present invention also provides a method for preparing a gallium nitride-based LED epitaxial structure, wherein the LED epitaxial structure is an epitaxial structure of a GaN-based light-emitting diode, and the equipment used is MOCVD, with trimethyl / ethyl gallium TMGa / TEGa, trimethyl aluminum TMAl, and ammonia NH3 as Ga source, Al source, and nitrogen source, respectively, and N2 as carrier gas. The N-type and P-type doping sources are silane SiH4 and bis(cyclopentadienyl)magnesium CP2Mg, respectively, and the method comprises:

[0074] S01, providing a substrate 1;

[0075] The substrate 1 includes but is not limited to a sapphire substrate 1 .

[0076] S02. Growing a buffer layer 2 and an N-type semiconductor layer 3 on the surface of the substrate 1; in one embodiment of the present invention, the N-type semiconductor layer 3 comprises an N-type doped GaN layer, which is not limited in the present invention;

[0077] Specifically, in this step, the substrate 1 is placed in an MOCVD reaction chamber, and high-purity hydrogen is introduced for hydrogenation for about 5 minutes at a temperature of about 1100°C. The temperature is then lowered to about 950°C to 970°C, and Al and nitrogen sources are introduced to grow an undoped AlN buffer layer 2 with a thickness of about 10nm to 20nm.

[0078] Next, the Al source is turned off and silane is introduced to grow a GaN layer with a thickness of about 1.3um to 1.8um and a Si-doped GaN layer (i.e., an N-type doped GaN layer) with a doping concentration of 1-10*10 18 cm -3 , forming the N-type semiconductor layer 3.

[0079] S03, growing an InGaN / GaN superlattice structure to obtain a first composite region 4;

[0080] Specifically, in this step, Figure 3 As shown, the temperature is lowered to 800-850°C, and by controlling the introduction of In source and Ga source, InGaN layers and GaN layers are alternately grown to form an InGaN / GaN superlattice structure with 3-10 periods; V-shaped pits are formed by utilizing the difference in growth rate of Ga atoms in different directions at the same temperature to obtain the first composite region 4.

[0081] S04, growing a stress transition layer 5, wherein the stress transition layer 5 comprises an InGaN material layer, and the stress transition layer 5 and the InGaN / GaN superlattice structure have the same In composition;

[0082] Specifically, in this step, the above temperature is maintained, and In source and Ga source are introduced to form an InGaN material layer with a thickness of D QW= 1-5 nm, inclusive; and the InGaN material layer and the InGaN / GaN superlattice structure have the same In composition; to finally obtain the stress transition layer 5.

[0083] S05, growing a second composite region 6, as shown, the second composite region 6 includes a plurality of quantum well period structures (6.1, 6.2, … 6.n) arranged in sequence along the growth direction, wherein each quantum well period structure includes alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer 5 is at least consistent with the thickness of the quantum well layer in the quantum well period structure adjacent thereto; Figure 2

[0084] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the thickness of the quantum well layer in the last quantum well period structure 6.n along the first direction is less than the thickness of the quantum well layer in any other quantum well period structure.

[0085] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth rate of the quantum barrier layer in the last quantum well period structure 6.n along the first direction is less than the growth rate of the quantum barrier layer in any other quantum well period structure.

[0086] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth temperature of the quantum barrier layer in the last quantum well period structure 6.n along the first direction is higher than the growth temperature of the quantum barrier layer in any other quantum well period structure.

[0087] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the first quantum well period structure 6.1 along the first direction includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; and the last quantum well period structure 6.n along the first direction includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

[0088] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth rate of the quantum barrier layer corresponding to each quantum well period structure along the first direction gradually decreases.

[0089] Further, based on the above-mentioned embodiments of the present application, in the second composite region 6, the growth temperature of the quantum barrier layer corresponding to each quantum well period structure along the first direction gradually increases.

[0090] ​In this step, as an optimal embodiment of the present application, the second recombination region 6 includes three quantum well periodic structures (i.e., n=3) arranged in sequence along the first direction, namely, a first quantum well periodic structure 6.1, a second quantum well periodic structure 6.2, and a third quantum well periodic structure 6.3; the thickness of the stress transition layer 5 is at least the same as the thickness of the quantum well layer in the first quantum well periodic structure 6.1. Furthermore, the thickness of the stress transition layer 5 is the same as the thickness of the quantum well layer in the second quantum well periodic structure 6.2. Furthermore, the first quantum well periodic structure 6.1 includes alternating stacks of AlGaN quantum barrier layers and InGaN quantum well layers; the second quantum well periodic structure 6.2 includes alternating stacks of GaN quantum barrier layers and InGaN quantum well layers; and the third quantum well periodic structure 6.3 includes alternating stacks of InGaN quantum barrier layers and InGaN quantum well layers.

[0091] Specifically, if Figure 4 In this step:

[0092] First, Ga source / Al source / silane is introduced for time t0, the growth temperature is T1 = 820 ~ 920 ° C, and the growth thickness is D QB1 AlGaN quantum barrier layer, where D QB1 =7nm~16nm, Ga source flow rate is F=(1~2)*a, a=1000~2000sccm; Si doping concentration is 1~8*10 17 cm -3 Then, the In source is introduced for a time of t1 to grow to a thickness of D QW1 InGaN quantum well layer, where D QW1 =D QW =1nm~5nm; further, it also includes: turning off the In source to grow a GaN layer with a thickness of 1~5nm to form a Cap layer, and the turning-off time is t2. Finally, repeat the above cycle, the growth cycle is N, N is 6~12, and finally the following is obtained Figure 5 The first quantum well periodic structure.

[0093] Then, the Ga source is introduced for a time of t3, the growth temperature is T, and the growth thickness is D. QB2 GaN quantum barrier layer, where D QB2 =7nm~16nm, T=850~950℃, Ga source flow rate is F1=a, a=1000~2000sccm, Si doping concentration is 1~8*10 17 cm -3 Then, the In source is introduced for a time of t4 to grow to a thickness of D QW2 InGaN quantum well layer, where D QW2 =DQW1 = D QW = 1 nm ~ 5 nm; further comprising: turning off the In source to grow a GaN layer with a thickness of 1 ~ 5 nm to form a Cap layer, and the turn-off time is t5. Finally, repeating the above cycle, the growth cycle is N, N is 6 ~ 12, and finally the second quantum well periodic structure as described in Figure 6 is obtained.

[0094] Next, the Ga source / In source is turned on for t6 time, the growth temperature is T2 = 880 ~ 980 ℃, and the growth thickness of the InGaN quantum barrier layer is D QB3 , wherein D QB3 = 7 nm ~ 16 nm, the Ga source flow is F2 = (0.3 ~ 1) * a, a = 1000 ~ 2000 sccm, and the Si doping concentration is 1 ~ 8 * 10 17 cm -3 -3; then, the InGaN quantum well layer with a growth thickness of D QW3 is turned on for t7 time, wherein D QW3 = 0.5 nm ~ 2 nm, the narrow well design of the last quantum well periodic structure is realized; further comprising: turning off the In source to grow a GaN layer with a thickness of 1 ~ 5 nm to form a Cap layer, and the turn-off time is t8. Finally, repeating the above cycle, the growth cycle is N, N is 1 ~ 3, and finally the second quantum well periodic structure as described in Figure 7 is obtained.

[0095] S06, making a P-type semiconductor layer 7;

[0096] In this step, the temperature is adjusted to 900-1000 ℃, the TMGa source, nitrogen source, and dimethyl magnesium are turned on to grow a P-type GaN layer, the thickness is 10-50 nm, the doping concentration is 1 * 10 19 cm -3 - 5 * 10 19 cm -3 -3; and annealing at 850-900 ℃ for 20-30 minutes under N2 atmosphere, and finally the P-type semiconductor layer 7 is formed.

[0097] The gallium nitride LED epitaxial structure provided by the technical scheme has the active layer comprising a first composite region 4, a stress transition layer 5 and a second composite region 6 arranged in sequence along a first direction; the first composite region 4 comprises an InGaN / GaN superlattice structure capable of forming a V-shaped pit; the stress transition layer 5 comprises an InGaN material layer, and the stress transition layer 5 and the InGaN / GaN superlattice structure have the same In component; the second composite region 6 comprises a plurality of quantum well period structures arranged in sequence along the first direction, wherein each quantum well period structure comprises quantum barrier layers and quantum well layers alternately stacked, and the thickness of the stress transition layer 5 is at least consistent with the thickness of the quantum well layer in the quantum well period structure adjacent to the stress transition layer 5. Thus, by setting the In component of the stress transition layer 5, stress transition between the InGaN / GaN superlattice structure (i.e. the first composite region 4) and the main light-emitting region (i.e. the second composite region 6) is realized, and the polarization effect caused by the lattice mismatch between the two materials in the InGaN / GaN superlattice structure is avoided from affecting the main light-emitting region; meanwhile, by setting the material and thickness of the stress transition layer 5, the stress transition layer 5 is equivalent to a front quantum well, so as to capture the carriers leaked through the penetrating dislocation center in the V-shaped pit and make the carriers radiate and recombine, thereby improving the internal quantum efficiency of the active layer and enhancing the brightness of the LED chip.

[0098] Secondly, by being arranged in the second composite region 6, the thickness of the quantum well layer in the last quantum well period structure along the first direction is smaller than the thickness of the quantum well layer in any other quantum well period structure. Based on this, the narrow well design of the last quantum well period structure is realized, which is beneficial to realizing the electron-hole wave function overlap in the remaining quantum well period structures to improve the radiation recombination probability in the region, thereby avoiding the imbalance between the hole and electron injection from causing most of the carriers to be recombined in the last quantum well period structure.

[0099] Then, by being arranged in the second composite region 6, the growth rate of the quantum barrier layer in the last quantum well period structure along the first direction is smaller than the growth rate of the quantum barrier layer in any other quantum well period structure. Based on this, the quantum barrier layer in the last quantum well period structure has the slowest growth rate, which can further sufficiently release stress, reduce stress accumulation and weaken the polarization field, thereby increasing the radiation recombination of the active region to better improve the light-emitting efficiency of the LED.

[0100] Next, by being arranged in the second composite region 6, the growth temperature of the quantum barrier layer in the last quantum well period structure along the first direction is higher than the growth temperature of the quantum barrier layer in any other quantum well period structure. Based on this, by growing the quantum barrier layer close to the main light-emitting region at a high temperature, the crystal defects are reduced, thereby obtaining the best crystal quality.

[0101] Finally, by setting in the second composite region 6, the first quantum well periodic structure along the first direction includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; the last quantum well periodic structure along the first direction includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers. Based on this, the quantum barrier layer of the first quantum well periodic structure is designed as an AlGaN layer, so as to improve the barrier height by doping Al, and the electron migration can be slowed down; and the quantum barrier in the last quantum well periodic structure is designed as an InGaN layer, which can reduce the lattice mismatch with the narrow well, so as to weaken the strong polarization field formed due to the lattice mismatch; on the other hand, the InGaN quantum barrier layer has a lower barrier height, which is beneficial to the hole injection; therefore, the electron and hole recombination can be further enhanced, so as to improve the light emitting efficiency.

[0102] The application further provides a preparation method of the gallium nitride LED epitaxial structure, which is simple in operation and easy to implement while achieving the above technical effects.

[0103] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0104] It should also be noted that, in the present document, the terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the article or device including the above element.

[0105] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the 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. A gallium nitride-based LED epitaxial structure, characterized in that: include: A substrate and an N-type semiconductor layer, an active layer, and a P-type semiconductor layer sequentially stacked on a surface of the substrate; the active layer comprises a first recombination region, a stress transition layer, and a second recombination region sequentially arranged along a first direction; wherein the first recombination region comprises an InGaN / GaN superlattice structure capable of forming a V-shaped pit; The stress transition layer includes an InGaN material layer, and the stress transition layer and the InGaN / GaN superlattice structure have the same In composition; The second recombination region includes a plurality of quantum well periodic structures arranged sequentially along the first direction, wherein each of the quantum well periodic structures includes alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer is at least consistent with the thickness of the quantum well layer in the quantum well periodic structure adjacent thereto; the first direction is perpendicular to the substrate and points from the substrate to the N-type semiconductor layer.

2. The GaN-based LED epitaxial structure according to claim 1, wherein: In the second recombination region, the thickness of the quantum well layer in the last quantum well periodic structure along the first direction is smaller than the thickness of the quantum well layer in any other quantum well periodic structure.

3. The GaN-based LED epitaxial structure according to claim 1, wherein: In the second recombination region, a growth rate of the quantum barrier layer in the last quantum well periodic structure along the first direction is lower than a growth rate of the quantum barrier layer in any other quantum well periodic structure.

4. The GaN-based LED epitaxial structure according to claim 1, wherein: In the second recombination region, the first quantum well periodic structure along the first direction includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; and the last quantum well periodic structure along the first direction includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

5. The GaN-based LED epitaxial structure according to claim 1, wherein: In the second recombination region, the growth rate of the quantum barrier layers corresponding to the quantum well periodic structures along the first direction gradually decreases.

6. The GaN-based LED epitaxial structure according to claim 1, wherein: In the second recombination region, the growth temperature of the quantum barrier layers corresponding to the quantum well periodic structures along the first direction gradually increases.

7. The GaN-based LED epitaxial structure according to any one of claims 1 to 6, characterized in that: The second recombination region includes three quantum well periodic structures arranged in sequence along the first direction, namely the first quantum well periodic structure, the second quantum well periodic structure and the third quantum well periodic structure; the thickness of the stress transition layer is at least the same as the thickness of the quantum well layer in the first quantum well periodic structure.

8. The GaN-based LED epitaxial structure according to claim 7, wherein: The thickness of the stress transition layer is consistent with the thickness of the quantum well layer in the second quantum well periodic structure.

9. The GaN-based LED epitaxial structure according to claim 7, wherein: The first quantum well periodic structure includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; the second quantum well periodic structure includes alternately stacked GaN quantum barrier layers and InGaN quantum well layers; and the third quantum well periodic structure includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

10. A method for preparing a gallium nitride-based LED epitaxial structure, characterized in that: include: providing a substrate; An N-type semiconductor layer, an active layer, and a P-type semiconductor layer are sequentially grown on the surface of the substrate; the active layer comprises a first recombination region, a stress transition layer, and a second recombination region sequentially arranged along a first direction; wherein the first recombination region comprises an InGaN / GaN superlattice structure capable of forming a V-shaped pit; The stress transition layer includes an InGaN material layer, and the stress transition layer and the InGaN / GaN superlattice structure have the same In composition; The second recombination region includes a plurality of quantum well periodic structures sequentially arranged along the first direction, wherein each of the quantum well periodic structures includes alternately stacked quantum barrier layers and quantum well layers, and the thickness of the stress transition layer is at least consistent with the thickness of the quantum well layer in the quantum well periodic structure adjacent thereto.

11. The method for preparing a GaN-based LED epitaxial structure according to claim 10, wherein: In the second recombination region, the thickness of the quantum well layer in the last quantum well periodic structure along the first direction is smaller than the thickness of the quantum well layer in any other quantum well periodic structure.

12. The method for preparing a GaN-based LED epitaxial structure according to claim 10, wherein: In the second recombination region, the first quantum well periodic structure along the first direction includes alternately stacked AlGaN quantum barrier layers and InGaN quantum well layers; and the last quantum well periodic structure along the first direction includes alternately stacked InGaN quantum barrier layers and InGaN quantum well layers.

13. The method for preparing a GaN-based LED epitaxial structure according to claim 12, wherein: In the second recombination zone, the Ga source flow rate is adjusted to achieve a growth rate of the quantum barrier layer in the last quantum well periodic structure along the first direction that is lower than the growth rate of the quantum barrier layer in any other quantum well periodic structure.

14. The method for preparing a GaN-based LED epitaxial structure according to claim 12, wherein: In the second recombination region, the growth temperature of the quantum barrier layers corresponding to the quantum well periodic structures along the first direction gradually increases.

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