Epitaxial structure for improving luminous efficiency and preparation method thereof

Abstract

The invention discloses an epitaxial structure for improving luminous efficiency and a preparation method of the epitaxial structure. The epitaxial structure comprises a substrate, an N-type semiconductor layer, a first current expansion layer, an active layer, a second current expansion layer and a P-type semiconductor layer which are sequentially stacked from bottom to top, the first current expansion layer is an InGaN (indium gallium nitride)-GaN (gallium nitride)-AlGaN (gallium nitride) composite layer, and two-dimensional electron gas is generated on a heterogeneous interface by the InGaN / GaN and the GaN / AlGaN; the second current expansion layer is an InGaN-GaN-AlGaN composite layer with an In component and an Al component gradually changed, and through the arrangement of a double-layer InGaN-GaN-AlGaN current expansion layer structure, electron leakage is reduced, hole injection is increased, carrier transportation is balanced, and the luminous efficiency of the device is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of light-emitting diodes, and particularly relates to an epitaxial structure for improving light-emitting efficiency and a preparation method thereof. BACKGROUND

[0002] III-V group GaN-based materials are widely concerned and applied in the fields of electricity and optics due to their excellent physical and chemical properties, such as a wide band gap, a high breakdown electric field and a high electron saturation velocity, for example, the mainstream Micro-LED and Mini-LED technologies on the market. However, in actual LED structure design, due to the significant difference in physical properties between electrons and holes (such as the difference in relative mass leading to the difference in mobility), the imbalance in carrier transport is difficult to avoid. Specifically, the relative mass of the electron is smaller, the mobility is higher, and the overflow leakage is prone to occur; and the relative mass of the hole is larger, the mobility is lower, and the injection efficiency is often insufficient. This imbalance in carrier injection seriously restricts the improvement of the light-emitting efficiency of the device. Therefore, inhibiting electron overflow and improving hole injection have become the key path to optimize the light-emitting efficiency of the LED.

[0003] It is worth noting that the traditional electron blocking layer blocks the electron leakage while hindering the hole injection, which in turn leads to low light-emitting efficiency. Therefore, developing a new carrier regulation structure to maintain the electron restraining ability while realizing the enhancement of hole injection has become a key technical path to break through the efficiency bottleneck of the LED. SUMMARY

[0004] The purpose of the application is to provide an epitaxial structure for improving light-emitting efficiency and a preparation method thereof, which reduces electron leakage, increases hole injection, balances carrier transport and improves the light-emitting efficiency of the device by setting a double-layer InGaN-GaN-AlGaN current expansion layer structure.

[0005] To achieve the above purpose, the application provides the following technical scheme: An epitaxial structure for improving light-emitting efficiency, comprising a substrate, an N-type semiconductor layer, a first current expansion layer, an active layer, a second current expansion layer and a P-type semiconductor layer which are sequentially stacked from bottom to top. The first current expansion layer is an InGaN-GaN-AlGaN composite layer, and the InGaN / GaN and GaN / AlGaN in the composite layer generate two-dimensional electron gas at the heterojunction interface; and the second current expansion layer is an InGaN-GaN-AlGaN composite layer with gradually changing In and Al components.

[0006] Optionally, the InGaN of the second current expansion layer is In x Ga 1-xN layer, wherein x gradually increases from 0 to x1, and then gradually decreases to 0, 0 < x1 < 0.1; the GaN of the second current spreading layer is a GaN layer; the AlGaN of the second current spreading layer is Al y Ga 1-y N layer, wherein y gradually increases from 0 to y1, and then gradually decreases to 0, 0 < y1 < 1.

[0007] Optionally, the In x Ga 1-x N layer is discontinuously doped with Mg.

[0008] Optionally, the In x Ga 1-x N layer, the GaN layer and the Al y Ga 1-y N layer are 10-30 nm, 1-10 nm and 10-30 nm respectively, and the end values are included.

[0009] Optionally, the active layer comprises quantum barrier layers, quantum well layers and GaN protective layers which are alternately stacked and grown, the quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, the In x Ga 1-x N layer has an In component less than that of the quantum well layer.

[0010] Optionally, the InGaN of the first current spreading layer is In z Ga 1-z N layer, wherein z ≥ 0.3, is N-type doped, and has a doping concentration of 1-5 × 10 18 cm -3 , including the end values; the GaN of the first current spreading layer is a GaN layer; the AlGaN of the first current spreading layer is Al w Ga 1-w N layer, wherein w ≥ 0.3.

[0011] Optionally, the In z Ga 1-z N layer, the GaN layer and the Al w Ga 1-w N layer are 10-30 nm, 5-10 nm and 10-30 nm respectively, and the end values are included.

[0012] Optionally, the InGaN-GaN-AlGaN composite layer structure of the first current spreading layer and the second current spreading layer each has 2-5 periods, including the end values.

[0013] Optionally, a buffer layer is arranged between the substrate and the N-type semiconductor, the buffer layer being an undoped GaN layer; a SSL layer is arranged between the first current spreading layer and the active layer, the SSL layer being a superlattice structure of 5-10 periods of InGaN / GaN, including end point values, and the V-shaped pits are formed by using the growth difference of Ga on different polar surfaces.

[0014] The application further provides a preparation method of the epitaxial structure for improving light emitting efficiency, comprising: growing an N-type semiconductor layer on a substrate; growing a first current spreading layer on the N-type semiconductor layer, the first current spreading layer being an InGaN-GaN-AlGaN composite layer, and two-dimensional electron gas being generated at the heterojunction interface of InGaN / GaN and GaN / AlGaN; growing an active layer on the first current spreading layer; growing a second current spreading layer on the active layer, the second current spreading layer being an InGaN-GaN-AlGaN composite layer with gradually changed In component and Al component; growing a P-type semiconductor layer on the second current spreading layer.

[0015] Optionally, growing the second current spreading layer on the active layer comprises: introducing Ga source, In source and NH3, and gradually increasing and then gradually decreasing the flow of NH3 and In source in t1 time, to form an In x Ga 1-x N layer with x gradually increasing from 0 to x1 and then gradually decreasing to 0, and 0 y Ga 1-y N layer with y gradually increasing from 0 to y1 and then gradually decreasing to 0, and 0

[0016] Optionally, the active layer comprises quantum barrier layers, quantum well layers and GaN protective layers which are alternately and periodically grown, the quantum well layers being InGaN layers, the quantum barrier layers being GaN layers, and the In x Ga 1-x N layer has an In component smaller than that of the quantum well layer.

[0017] Optionally, the InGaN of the first current spreading layer is In z Ga 1-zN layer, wherein, z≥0.3; the GaN of the first current spreading layer is a GaN layer; the AlGaN of the first current spreading layer is Al w Ga 1-w N layer, wherein, w≥0.3.

[0018] Optionally, a buffer layer is further grown between the substrate and the N-type semiconductor, the buffer layer being an undoped GaN layer; an SSL layer is further grown between the first current spreading layer and the active layer, the SSL layer being a superlattice structure of 5-10 periods of InGaN / GaN, and V-shaped pits are formed by using the growth difference of Ga on different polar surfaces.

[0019] After the above scheme is adopted, the application has the following advantages: 1. The first current spreading layer close to the N-type region is an InGaN-GaN-AlGaN composite layer, and the two-dimensional electron gas formed at the heterojunction of InGaN / GaN and GaN / AlGaN in the composite layer can increase the current spreading capacity and improve the anti-static capacity of the device; at the same time, the band step characteristics of InGaN-GaN-AlGaN are beneficial to the hysteresis of electrons, can slow down the migration rate of electrons, reduce the overflow of electrons, and further reduce the imbalance of carrier transport, thus playing a role in blocking electrons, which is beneficial to the injection of holes in the P-type layer into a deeper MQW (active layer) region, and improves the light emitting efficiency of the device.

[0020] 2. The second current spreading layer close to the P-type region is an InGaN-GaN-AlGaN composite layer with gradually changing In component and Al component, wherein the InGaN with gradually changing In component can reduce the valence band barrier height and promote the injection of holes, and the AlGaN with gradually changing Al component can increase the conduction band barrier height and reduce the leakage of electrons.

[0021] 3. In the second current spreading layer, the gradually changing In component and Al component are both gradually increased and then gradually decreased, and the lattice difference between the two materials can adjust and control the in-plane tensile stress of InGaN-GaN and the in-plane compressive stress of GaN-AlGaN, so as to weaken the polarization electric field, reduce the band bending, increase the overlap of electron-hole wave functions, and improve the radiative recombination light emission.

[0022] 4. In the InGaN of the second current spreading layer, Mg is intermittently doped while the In component is gradually changed, which can improve the injection of holes without introducing new impurities, maintain the material crystal quality, and improve the light emitting efficiency of the device.

[0023] 5. While the In source and Al source are gradually introduced into the second current spreading layer, the NH3 flow is also gradually introduced, so that the InGaN is grown by using the In source, the AlGaN is grown by using the Al source, and the GaN is grown by using the NH3 flow. x Ga 1-xWhen growing the N layer, the gradual change trend of NH3 flow is the same as the In source, so that the high NH3 flow creates a high V / III ratio, which is conducive to maintaining the crystal quality of InGaN, and can maximize the maintenance of the material crystal quality; and when growing the Al y Ga 1-y When growing the N layer, the gradual change trend of NH3 flow is the same as the In source, so that the high NH3 flow creates a high V / III ratio, which is conducive to maintaining the crystal quality of InGaN, and can maximize the maintenance of the material crystal quality; and when growing the Al

[0024] 6、The InGaN-GaN-AlGaN structure designed by the application can complement each other in reducing electron leakage, increasing hole injection and balancing carrier transport, and produce higher combination benefits.

[0025] 7、The InGaN-GaN-AlGaN composite layer structure of the first current expansion layer and the second current expansion layer can also be constructed into a multi-period structure, further expanding the beneficial effects. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the epitaxial structure of the application; Figure 2 It is a conduction band schematic diagram of the InGaN-GaN-AlGaN of the second current expansion layer of the application; Figure 3 It is a growth source schematic diagram of the InGaN-GaN-AlGaN of the second current expansion layer of the application; Figure 4 It is a process flow chart of the preparation method of the application.

[0027] Label explanation: 1, substrate; 2, buffer layer; 3, N-type semiconductor layer; 4, first current expansion layer; 5, SSL layer; 6, active layer; 7, second current expansion layer; 8, P-type semiconductor layer. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application, and all the range values of the application all include the end point values.

[0029] Please refer to Figure 1The application provides an epitaxial structure for improving light emitting efficiency, which comprises a substrate 1, a buffer layer 2, an N-type semiconductor layer 3, a first current spreading layer 4, an SSL layer 5, an active layer 6, a second current spreading layer 7 and a P-type semiconductor layer 8 which are sequentially stacked from bottom to top; wherein the first current spreading layer 4 is an InGaN-GaN-AlGaN composite layer, the composite layer structure can further block misplacement and improve crystal quality, the InGaN / GaN and GaN / AlGaN in the composite layer can generate two-dimensional electron gas at the heterojunction interface (a large enough component difference can form two-dimensional electron gas at the interface), the current spreading capacity and the anti-static capacity of the device can be improved; meanwhile, the band step characteristics of the InGaN-GaN-AlGaN are beneficial to hysteresis electron, the migration rate of the electron can be slowed down, the electron overflow can be reduced, the carrier transport imbalance can be reduced, the electron can be blocked, the P-type layer hole injection into a deeper MQW (active layer 6) region is facilitated, and the light emitting efficiency of the device is improved.

[0030] Optionally, the InGaN of the first current spreading layer 4 is In z Ga 1-z N layer, wherein z is greater than or equal to 0.3, the N-type doping and the doping concentration are 1-5×10 18 cm -3 ; the GaN of the first current spreading layer 4 is an undoped GaN layer; the AlGaN of the first current spreading layer 4 is an Al w Ga 1-w N layer, wherein w is greater than or equal to 0.3.

[0031] Optionally, the thicknesses of the In z Ga 1-z N layer, the GaN layer and the Al w Ga 1-w N layer in the first current spreading layer 4 are respectively 10-30 nm, 5-10 nm and 10-30 nm.

[0032] Furthermore, the second current spreading layer 7 is an InGaN-GaN-AlGaN composite layer with gradually changed In component and Al component, wherein the InGaN with gradually changed In component can reduce the valence band barrier height and promote hole injection, and the AlGaN with gradually changed Al component can increase the conduction band barrier height and reduce electron leakage.

[0033] Specifically, the InGaN of the second current spreading layer 7 is an In x Ga 1-x N layer with gradually changed In component in the direction of the P-type semiconductor layer 8, that is, the In x Ga 1-xThe band gap of the N layer decreases with the increase of x, and the conduction band of the second current spreading layer 7 changes as shown in Figure 2 The GaN layer of the second current spreading layer 7 is a non-gradual GaN layer, and the AlGaN layer of the second current spreading layer 7 is an AlGaN layer with an Al component gradually changing along the growth direction. y Ga 1-y N layer, wherein y gradually increases from 0 to y1, and then gradually decreases to 0, and 0 < y1 < 1, and the Al y Ga 1-y N layer increases with the increase of y, and the conduction band changes as shown in Figure 2 By adjusting the gradual component and the lattice difference between the two materials, the InGaN-GaN in-plane tensile stress and the GaN-AlGaN in-plane compressive stress can be adjusted to weaken the polarization electric field, reduce the energy band bending, increase the electron-hole wave function overlap, and improve the radiation recombination light emission.

[0034] Optionally, the In x Ga 1-x N layer is discontinuously doped with Mg, and the Mg has a low activation energy in the In x Ga 1-x N, which is beneficial to the incorporation of Mg, and can improve the hole injection without introducing new impurities, maintaining the material crystal quality and improving the light emission efficiency of the device.

[0035] Optionally, the thicknesses of the In x Ga 1-x N layer, the GaN layer and the Al y Ga 1-y N layer in the second current spreading layer 7 are 10-30 nm, 1-10 nm and 10-30 nm, respectively.

[0036] Optionally, the InGaN-GaN-AlGaN composite layer structure of the first current spreading layer 4 and the second current spreading layer 7 can also be constructed as a multi-period structure to further expand the beneficial effects, and in a preferred embodiment, the InGaN-GaN-AlGaN composite layer structure is constructed as 2-5 periods.

[0037] Optionally, the active layer 6 includes quantum barrier layers, quantum well layers and GaN protective layers alternately stacked and grown in periods, and the growth period is 5-10 periods, the quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, and the In x Ga 1-x N layer in the second current spreading layer 7 has an In component smaller than that of the quantum well layer, so as to reduce the absorption of the emitted light in the quantum well layer by the In x Ga 1-x N layer, and further improve the light emission efficiency of the device.

[0038] Optionally, the growth temperature of the quantum barrier layer is 800-900℃, the thickness is 10-20nm, and the doping concentration is 3-8×10 17 cm -3 ; the growth temperature of the quantum well layer is 700-800℃, the thickness is 1-4nm; and the growth thickness of the GaN protective layer is 10-20A.

[0039] Optionally, the SSL layer 5 is a short-period superlattice structure of 5-10 periods of InGaN / GaN, which utilizes the growth difference of Ga on different polar surfaces to form V-pits, so as to reduce the non-radiative recombination probability, enhance the hole injection, and optimize the electrical performance. The growth temperature of the SSL layer 5 is 800-850℃.

[0040] Optionally, the type of the substrate 1 is not limited in the present application, for example, the substrate 1 includes any one of sapphire, silicon carbide, silicon, gallium nitride, and aluminum nitride, and the c-plane sapphire substrate 1 is preferred in the embodiment.

[0041] Optionally, the buffer layer 2 is an undoped GaN layer, the thickness is 2.0-2.5μm, and the growth temperature is 1000-1100℃. The buffer layer 2 is used to reduce the lattice mismatch between the sapphire substrate 1 and the subsequently grown material by growing a high-quality GaN layer.

[0042] Optionally, a low-temperature nucleation layer (not shown in the figure) of undoped GaN is further grown between the buffer layer 2 and the sapphire substrate 1, the thickness is 15-25nm, and the growth temperature is 800-900℃.

[0043] Optionally, the N-type semiconductor layer 3 is an N-type Si-doped GaN layer, the doping concentration is 1-5×10 19 cm -3 , and the N-type semiconductor layer 3 is used to provide an N-type contact.

[0044] Optionally, the P-type semiconductor layer 8 is a P-type Mg-doped GaN layer, the doping concentration is 5-10×10 18 cm -3 , the growth temperature is 850-900℃, and the P-type semiconductor layer 8 is used to provide a P-type contact.

[0045] The application further provides a preparation method of an epitaxial structure for improving light emitting efficiency, which specifically adopts a metal organic chemical vapor deposition (MOCVD) method to grow, from bottom to top on a substrate 1, a low-temperature nucleation layer, a buffer layer 2, an N-type semiconductor layer 3, a first current spreading layer 4, an SSL layer 5, an active layer 6, a second current spreading layer 7 and a P-type semiconductor layer 8. The substrate 1 includes but is not limited to a sapphire substrate 1, and in this embodiment, the sapphire substrate 1 is taken as an example, and trimethyl / ethyl gallium (TMGa / TEGa), trimethyl aluminum (TMAl) and ammonia (NH3) are taken as Ga source, Al source and N source respectively, N2 is taken as carrier gas, and silane (SiH4) and cyclopentadienyl magnesium (CP2Mg) are taken as N-type and P-type doping sources respectively.

[0046] Please refer to Figure 4 , and the preparation method specifically includes the following steps. S1, growing a low-temperature nucleation layer on the substrate 1, including: placing the sapphire substrate 1 into a MOCVD reaction chamber, introducing high-purity hydrogen into the MOCVD reaction chamber at a high-temperature environment of 1100℃ for 5-10 min, then reducing the temperature to 800-900℃, introducing a TEGa source and an N source to grow a 15-25 nm-thick and undoped GaN low-temperature nucleation layer.

[0047] S2, growing a buffer layer 2 on the low-temperature nucleation layer, including: after the low-temperature nucleation layer is grown, continuing to increase the temperature to 1000-1100℃, closing the TEGa source, introducing a TMGa source to grow a 2.0-2.5 μm-thick and undoped GaN buffer layer 2, and the purpose of growing the buffer layer 2 is to reduce the lattice mismatch between the sapphire substrate 1 and the subsequently grown material by growing a high-quality GaN layer.

[0048] S3, growing an N-type semiconductor layer 3 on the buffer layer 2, including: after the buffer layer 2 is grown, introducing silane to grow a 1-2 μm-thick and Si-doped N-type semiconductor layer 3, and the doping concentration is 1-5×10 19 cm -3 , and the purpose of growing the N-type semiconductor layer 3 is to provide an N-type contact.

[0049] S4, growing a first current spreading layer 4 on the N-type semiconductor layer 3, including: after the N-type semiconductor layer 3 is grown, introducing an In source to grow a 10-30 nm-thick In z Ga 1-z N layer, where z≥0.3, and the doping concentration is 1-5×10 18 cm -3 , then closing the silane and In source, growing a 5-10 nm-thick GaN layer, and then introducing an Al source to grow a 10-30 nm-thick Al w Ga1-w N layer, wherein w≥0.3, the composite layer structure can further block dislocations, improve the crystal quality, while using InGaN / GaN and GaN / AlGaN at the heterojunction interface to generate two-dimensional electron gas, which can increase the current spreading ability, in addition, the band step characteristics of InGaN-GaN-AlGaN can also play a role in delaying electrons, reducing electron overflow, and relieving carrier transport imbalance.

[0050] Optionally, the InGaN-GaN-AlGaN composite layer structure of the first current spreading layer 4 can be constructed as a multi-period structure, preferably 2-5 periods, to further expand the above beneficial effects.

[0051] S5, growing an SSL layer 5 on the first current spreading layer 4, including: After the first current spreading layer 4 is grown, the temperature is lowered to 800-850°C, the In source and Ga source are introduced, and 5-10 periods of InGaN / GaN are alternately grown. The SSL layer 5 is a short-period superlattice structure of InGaN / GaN, which utilizes the growth difference of Ga on different polar surfaces to form V-pits, which can reduce the non-radiative recombination probability, enhance hole injection, and optimize the electrical performance.

[0052] S6, growing an active layer 6 on the SSL layer 5, including: After the SSL layer 5 is grown, the temperature is lowered to 800-900°C, and TEGa (Ga source) and SiH4 are introduced to grow a quantum barrier layer (QB) with a thickness of 10-20 nm and a doping concentration of 3-8×10 17 cm -3 -2. The growth of the quantum well layer (QW) is continued to 700-800°C, TEGa and TMIn are introduced, SiH4 and H2 are closed, and a 1-4 nm thick quantum well layer (QW) is grown. The quantum well layer is an InGaN layer. Then the Ga source is continued to be introduced, and a 10-20A thick GaN protective layer is grown. Finally, H2 is opened, and the temperature is raised to the growth temperature of the QB. Repeat the above growth process for 5-10 periods to complete the entire active layer 6 growth process.

[0053] S7, growing a second current spreading layer 7 on the active layer 6, including: The second current spreading layer 7 is started to be grown on the last quantum barrier layer, as shown in Figure 3 , first introduce the Ga source and the In source, gradually increase the flow of NH3 and the In source for t1 time, then gradually decrease to form a 10-30 nm thick In x Ga 1-xN layer, wherein x increases from 0 to x1 and then decreases to 0, 0 < x1 < 0.1, high NH3 flow rate is conducive to maintaining the crystal quality of InGaN layer; and after the t' time of inputting Ga source, In source and NH3, Mg is intermittently doped for T' time, the activation energy of Mg in InGaN is low, which is conducive to the incorporation of Mg, intermittent doping of Mg can also introduce new impurities under the premise of improving hole injection, maintain the crystal quality of the material and improve the luminous efficiency of the device, in addition, T' < t1 and t' > 0 can ensure that Mg does not penetrate into the active region to form a non-radiative recombination center.

[0054] Then the In source is turned off, a 1-10 nm thick GaN layer is grown, the Al source is continuously input, the Al source flow first increases and then decreases, and NH3 with a flow trend opposite to that of Al is input, the purpose is to reduce the pre-reaction when growing AlGaN, and low NH3 flow rate is conducive to the growth of AlGaN material system, and an AlGaN layer with a thickness of 10-30 nm and gradually changing Al component is grown. y Ga 1-y N, wherein y increases from 0 to y1 and then decreases to 0, 0 < y1 < 1.

[0055] Through the above-mentioned adjustment of gradually changing components and the lattice difference of two materials, the InGaN-GaN in-plane tensile stress and the GaN-AlGaN in-plane compressive stress can be adjusted to weaken the polarization electric field, reduce the energy band bending, increase the electron-hole wave function overlap, and improve the radiative recombination light emission Optionally, the In content in the second current spreading layer 7 x Ga 1-x The In content of the InGaN-GaN-AlGaN composite layer structure of the second current spreading layer 7 should be less than the In content of the quantum well layer, so as to reduce the absorption of the emitted light in the quantum well layer by the InGaN-GaN-AlGaN composite layer structure of the second current spreading layer 7, and further improve the luminous efficiency of the device. x Ga 1-x N layer, the In content of the InGaN-GaN-AlGaN composite layer structure of the second current spreading layer 7 should be less than the In content of the quantum well layer, so as to reduce the absorption of the emitted light in the quantum well layer by the InGaN-GaN-AlGaN composite layer structure of the second current spreading layer 7, and further improve the luminous efficiency of the device.

[0056] Optionally, the InGaN-GaN-AlGaN composite layer structure of the second current spreading layer 7 can be constructed as a multi-period structure, and preferably 2-5 periods are constructed, so as to further expand the above-mentioned beneficial effects.

[0057] S8, growing a P-type semiconductor layer 8 on the second current spreading layer 7, comprising: After the second current spreading layer 7 is grown, the P-type doping source cyclopentadienyl magnesium CP2Mg is then input, and annealing is performed at 850-900°C for 20-30 minutes in N2 atmosphere, so as to grow a P-type semiconductor layer 8 with a doping concentration of 1-5×10 19 cm -3 The pressure of the whole reaction and growth is 100-300 torr, and the purpose of growing the P-type semiconductor layer 3 is to provide a P-type contact.

[0058] As can be known from the above description, the epitaxial structure made by the manufacturing method, by designing the double-layer InGaN-GaN-AlGaN structure, on the one hand, the InGaN-GaN-AlGaN composite layer is inserted close to the N-type region, the two-dimensional electron gas generated at the heterojunction interface is used to increase the current expansion, and the band step characteristics are used to achieve the purpose of delaying electrons and reducing electron overflow; on the other hand, the composition-gradual InGaN-GaN-AlGaN composite layer is inserted close to the P-type region, the height of the valence band barrier is reduced, the hole injection is increased, the stress is regulated, the polarization electric field of the active region is weakened, and the light emitting efficiency of the device is effectively improved. Moreover, by designing the double-layer InGaN-GaN-AlGaN structure, the mutual complementation in reducing electron leakage, increasing hole injection, and balancing carrier transport, etc. can be achieved, and higher combination benefits can be generated.

[0059] It is worth noting that the thickness of the substrate 1, the buffer layer 2, the N-type semiconductor layer 3, the first current expansion layer 4, the SSL layer 5, the active layer 6, the second current expansion layer 7, and the P-type semiconductor layer 8 shown in the drawings of the present application are only examples and do not represent the true thickness. Moreover, the true proportions between the substrate 1, the buffer layer 2, the N-type semiconductor layer 3, the first current expansion layer 4, the SSL layer 5, the active layer 6, the second current expansion layer 7, and the P-type semiconductor layer 8 are not as shown in the drawings, but are only for reference.

[0060] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0061] 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. An epitaxial structure for improving luminous efficiency, characterized by: The invention comprises a substrate, an N-type semiconductor layer, a first current spreading layer, an active layer, a second current spreading layer, and a P-type semiconductor layer which are sequentially stacked from bottom to top; The first current spreading layer is an InGaN-GaN-AlGaN composite layer, in which InGaN / GaN and GaN / AlGaN generate two-dimensional electron gas at the heterojunction interface; the second current spreading layer is an InGaN-GaN-AlGaN composite layer with a gradient In component and Al component.

2. The epitaxial structure for improving luminous efficiency according to claim 1, wherein: The InGaN of the second current spreading layer is an In x Ga 1-x N layer in which x gradually changes from 0 to x1 and then gradually decreases to 0, where 0 < x1 < 0.1; the GaN of the second current spreading layer is a GaN layer; the AlGaN of the second current spreading layer is an Al y Ga 1-y N layer in which y gradually changes from 0 to y1 and then gradually decreases to 0, where 0 < y1 < 1.

3. The epitaxial structure for improving luminous efficiency according to claim 2, wherein: In x Ga 1-x The N layer is discontinuously doped with Mg.

4. The epitaxial structure for improving luminous efficiency according to claim 2, wherein: In in the second current spreading layer x Ga 1-x N layer, GaN layer and Al y Ga 1-y The thickness of the N layer is 10-30 nm, 1-10 nm and 10-30 nm, respectively, and all include endpoint values.

5. The epitaxial structure for improving luminous efficiency according to claim 2, wherein: The active layer includes a quantum barrier layer, a quantum well layer and a GaN protective layer that are alternately stacked and periodically grown. The quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, and the InGaN layer is a GaN layer. x Ga 1-x The In composition of the N layer is smaller than the In composition of the quantum well layer.

6. The epitaxial structure for improving luminous efficiency according to claim 1, wherein: The InGaN of the first current spreading layer is In z Ga 1-z N layer, where z≥0.3, is N-type doped, with a doping concentration of 1-5×10 18 cm -3 , including endpoint values; the GaN of the first current spreading layer is a GaN layer; the AlGaN of the first current spreading layer is Al w Ga 1-w N layers, where w ≥ 0.

3.

7. The epitaxial structure for improving luminous efficiency according to claim 6, wherein: In the first current spreading layer z Ga 1-z N layer, GaN layer and Al w Ga 1-w The thickness of the N layer is 10-30 nm, 5-10 nm and 10-30 nm, respectively, and all include the endpoint values.

8. The epitaxial structure for improving luminous efficiency according to claim 1, wherein: The InGaN-GaN-AlGaN composite layer structures of the first current spreading layer and the second current spreading layer both have 2 to 5 periods, including endpoint values.

9. The epitaxial structure for improving luminous efficiency according to claim 1, wherein: A buffer layer is also provided between the substrate and the N-type semiconductor, and the buffer layer is an undoped GaN layer; an SSL layer is also provided between the first current spreading layer and the active layer, and the SSL layer is a superlattice structure of InGaN / GaN grown in 5-10 cycles, including endpoint values, and utilizes the growth difference of Ga on different polarity planes to form a V-shaped pit.

10. A method for preparing an epitaxial structure with improved luminous efficiency according to any one of claims 1 to 9, characterized in that: include: growing an N-type semiconductor layer on a substrate; Growing a first current spreading layer on the N-type semiconductor layer, wherein the first current spreading layer is an InGaN-GaN-AlGaN composite layer, wherein the InGaN / GaN and GaN / AlGaN generate a two-dimensional electron gas at the heterojunction interface; growing an active layer on the first current spreading layer; growing a second current spreading layer on the active layer, wherein the second current spreading layer is an InGaN-GaN-AlGaN composite layer with a gradient In component and Al component; A P-type semiconductor layer is grown on the second current spreading layer.

11. The method for preparing an epitaxial structure with improved luminous efficiency according to claim 10, wherein: Growing a second current spreading layer on the active layer includes: Introduce Ga source, In source and NH3. Within the time t1, the flow rates of NH3 and In source first gradually increase and then gradually decrease, forming an InGaN layer with a gradually changing In composition, where x gradually increases from 0 to x1 and then gradually decreases to 0, and 0 < x1 < 0.

1. After the time t' of introducing Ga source, In source and NH3, Mg is intermittently doped within the time T', where T' < t1 and t' > 0. Then turn off the In source and grow the GaN layer. Then continue to introduce the Al source. The flow rate of the Al source first gradually increases and then gradually decreases, and at the same time, NH3 with a flow rate trend opposite to that of the Al source is introduced, forming an AlGaN layer with a gradually changing Al composition, where y gradually increases from 0 to y1 and then gradually decreases to 0, and 0 < y1 < 1. x Ga 1-x N layer, where x gradually increases from 0 to x1 and then gradually decreases to 0, 0 < x1 < 0.1; after the time t' of introducing Ga source, In source and NH3, Mg is intermittently doped within the time T', where T' < t1 and t' > 0; then turn off the In source and grow the GaN layer; then continue to introduce the Al source. The flow rate of the Al source first gradually increases and then gradually decreases, and at the same time, NH3 with a flow rate trend opposite to that of the Al source is introduced, forming an AlGaN layer with a gradually changing Al composition, where y gradually increases from 0 to y1 and then gradually decreases to 0, 0 < y1 < 1. y Ga 1-y N layer, where y gradually increases from 0 to y1 and then gradually decreases to 0, 0 < y1 < 1.

12. The method for preparing an epitaxial structure with improved luminous efficiency according to claim 11, wherein: The active layer includes a quantum barrier layer, a quantum well layer and a GaN protective layer that are alternately stacked and periodically grown. The quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, and the InGaN layer is a GaN layer. x Ga 1-x The In composition of the N layer is smaller than the In composition of the quantum well layer.

13. The method for preparing an epitaxial structure with improved luminous efficiency according to claim 10, wherein: The InGaN of the first current spreading layer is In z Ga 1-z N layer, wherein z≥0.3; the GaN of the first current spreading layer is a GaN layer; the AlGaN of the first current spreading layer is an Al w Ga 1-w N layers, where w ≥ 0.

3.

14. The method for preparing an epitaxial structure with improved luminous efficiency according to claim 10, wherein: A buffer layer is also grown between the substrate and the N-type semiconductor, and the buffer layer is an undoped GaN layer; an SSL layer is also grown between the first current spreading layer and the active layer, and the SSL layer is a superlattice structure of InGaN / GaN grown in 5-10 cycles, and V-shaped pits are formed by utilizing the growth difference of Ga on different polarity planes.

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