An LED epitaxial structure for improving luminous efficiency and a manufacturing method thereof

Abstract

The present application discloses an LED epitaxial structure for improving luminous efficiency and a manufacturing method thereof. The LED epitaxial structure includes: a substrate, and a buffer layer, an N-GaN layer, a multi-quantum well structure, and a P-GaN layer sequentially grown on one surface of the substrate; wherein, the multi-quantum well structure is formed by alternating multiple quantum barriers and quantum wells. The quantum well includes an InN layer, an InGaN layer, a GaN layer, and an AlInGaN layer sequentially grown on the quantum barrier. The GaN layer and the AlInGaN layer constitute a Cap layer. Between the N-GaN layer and the P-GaN layer, the Cap layer adopts a growth mode with a gradual change of Al / In, which can play a role in polarization matching, form a high conduction band barrier, and reduce electron leakage. And in the initial stage of the growth of the quantum well, a growth mode of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor optoelectronic technologies, and particularly to an LED epitaxial structure for improving luminous efficiency and a manufacturing method thereof. Background Art

[0002] Currently, AlInGaN-based light-emitting materials are playing more and more applications in the fields of display and lighting due to their physical and chemical properties such as large bandgap, high breakdown electric field, and high electron saturation mobility. And the multi-quantum well InGaN / GaN, as the active region of the LED, is particularly important for the optical properties of the LED. However, in the long wavelength band, such as green light, yellow light, red light, etc., as the In component in the active region InGaN becomes higher and higher, its crystal quality deteriorates and the defects increase, thereby reducing the luminous efficiency of the LED. And there is a serious lattice mismatch and low miscibility between InN and GaN, which easily results in In clusters in the InGaN / GaN active region, thereby causing phenomena such as non-uniform light emission and impure color rendering. In addition, due to its spontaneous polarization and piezoelectric polarization, group III nitrides will form a built-in electric field, which easily generates the quantum-confined Stark effect and exacerbates electron leakage. To solve this problem, currently, a common method is to insert an AlGaN electron blocking layer (EBL) between the InGaN / GaN active region and the P layer to increase the conduction band electron barrier and reduce electron leakage. However, this method also hinders the hole from transporting from the P layer to the active region, thereby hindering the recombination of electrons and holes in the active region and thus affecting the luminous efficiency of the LED.

[0003] Therefore, reducing electron leakage, increasing hole injection efficiency, weakening the strong polarization electric field, and promoting the efficient recombination of carriers in the active region have become urgent problems to be solved for improving the luminous efficiency of the LED. Summary of the Invention

[0004] In view of this, the present invention provides an LED epitaxial structure for improving luminous efficiency and a manufacturing method thereof. By adopting the Cap layer design of GaN + AlInGaN and the growth mode with a gradual change in the Al-to-In ratio, it can not only achieve polarization matching but also form a high conduction band barrier to reduce electron leakage.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An LED epitaxial structure for improving luminous efficiency, comprising:

[0007] a substrate, and a buffer layer, an N-GaN layer, a multi-quantum well structure, and a P-GaN layer sequentially grown on one surface of the substrate;

[0008] Among them, the multi-quantum well structure is formed by alternating multiple quantum barriers and quantum wells. The quantum well includes an InN layer, an InGaN layer, a GaN layer, and an AlInGaN layer grown in sequence on the quantum barrier. The GaN layer and the AlInGaN layer constitute the Cap layer. Between the N-GaN layer and the P-GaN layer, the Cap layer adopts a growth method with a gradually changing Al-to-In ratio, which can achieve polarization matching, form a high conduction band barrier, and reduce electron leakage. Moreover, in the initial stage of the growth of the quantum well, a growth method of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

[0009] Preferably, in the above LED epitaxial structure, the growth period of the quantum barrier is N + 1, where N is 6 to 12;

[0010] The thickness of the 1st to the (N - 3)th quantum barriers is D QB1 , D QB1 = 7 to 16 nm;

[0011] The thickness of the (N - 1)th and the (N - 2)th quantum barriers is D QB2 , D QB1 -D QB2 ≥ 2 to 6 nm;

[0012] The thickness of the Nth quantum barrier is D QB3 , D QB2 -D QB3 ≤ 2 to 4 nm;

[0013] The thickness of the (N + 1)th quantum barrier is D QB4 , D QB4 = 18 to 30 nm.

[0014] Preferably, in the above LED epitaxial structure, the 1st to the Nth quantum barriers are all GaN layers, and the (N + 1)th quantum barrier is an AlGaN layer.

[0015] Preferably, in the above LED epitaxial structure, the growth period of the quantum well is N, where N is 6 to 12;

[0016] The In composition in the 1st to the (N - 4)th quantum wells is X and gradually increases, 0.05 ≤ X ≤ 0.3;

[0017] The In composition in the (N - 3)th and the (N - 2)th quantum wells remains unchanged, being 0.25 to 0.3;

[0018] The In composition in the (N - 1)th and the Nth quantum wells is Y and gradually decreases, 0.1 ≤ Y ≤ 0.2.

[0019] Preferably, in the above LED epitaxial structure, the thickness of the Cap layer is 1 to 5 nm.

[0020] Preferably, in the above LED epitaxial structure, it further includes:

[0021] An undoped AlN low-temperature nucleation layer disposed between the substrate and the buffer layer;

[0022] A contact layer disposed on the surface of the P-GaN layer facing away from the multi-quantum well structure;

[0023] A P electrode disposed on the surface of the contact layer facing away from the P-GaN layer;

[0024] An N electrode disposed on the surface of the N-GaN layer facing away from the buffer layer.

[0025] Preferably, in the above LED epitaxial structure, the thickness of the N-GaN layer is 1.3 to 1.8 μm, and the doping concentration is 1 - 10×10 18 cm -3 .

[0026] Preferably, in the above LED epitaxial structure, the thickness of the P-GaN layer is 100 to 150 nm, and the doping concentration is 5 - 10×10 18 cm -3 .

[0027] Preferably, in the above LED epitaxial structure, the substrate is a sapphire substrate.

[0028] The present invention also provides a method for manufacturing an LED epitaxial structure for improving luminous efficiency, and the manufacturing method includes:

[0029] Providing a substrate;

[0030] Sequentially growing a buffer layer, an N-GaN layer, a multi-quantum well structure, and a P-GaN layer on one surface of the substrate;

[0031] Wherein, the multi-quantum well structure is formed by alternating multiple quantum barriers and quantum wells. The quantum well includes an InN layer, an InGaN layer, a GaN layer, and an AlInGaN layer sequentially grown on the quantum barrier. The GaN layer and the AlInGaN layer constitute the Cap layer. And between the N-GaN layer and the P-GaN layer, the Cap layer adopts a growth mode with a gradual change in the Al ratio to In, which can play a role in polarization matching, form a high conduction band barrier, and reduce electron leakage. And in the initial stage of the growth of the quantum well, a growth mode of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

[0032] As can be seen from the above description, in the LED epitaxial structure and its manufacturing method for improving luminous efficiency provided by the technical solution of the present invention, the Cap layer design of GaN + AlInGaN and the growth mode with a gradual change in the Al-to-In ratio can not only achieve polarization matching but also form a high conduction band barrier to reduce electron leakage.

[0033] Moreover, in the initial stage of the growth of the quantum well, a growth mode of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

[0034] At the same time, the quantum barrier adopts a growth mode with a gradual change in thickness, and the quantum well adopts a growth mode with a gradual change in In composition, which can reduce the lattice mismatch between materials, weaken the strong polarization electric field, and improve the luminous efficiency of the LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0036] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present application. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present application.

[0037] Figure 1 It is a schematic diagram of an LED epitaxial structure for improving luminous efficiency provided by an embodiment of the present invention;

[0038] Figure 2 It is a schematic diagram of another LED epitaxial structure for improving luminous efficiency provided by an embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the conduction band of a MQW provided by an embodiment of the present invention;

[0040] Figure 4 It is a schematic diagram of the growth source for a multi-quantum well structure provided by an embodiment of the present invention;

[0041] Figures 5 - 12 It is a process flow chart of a manufacturing method for an LED epitaxial structure for improving luminous efficiency provided by an embodiment of the present invention. Detailed implementation manners

[0042] The embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0043] As described in the background art, AlInGaN-based light-emitting materials play an increasingly important role in the fields of display and lighting due to their physical and chemical properties such as large bandgap, high breakdown electric field, and high electron saturation mobility. The multi-quantum well InGaN / GaN, as the active region of the LED, is particularly important for the optical properties of the LED. However, in the long wavelength band, such as green light, yellow light, red light, etc., as the In composition in the active region InGaN increases, its crystal quality deteriorates and the defects increase, thereby reducing the light-emitting efficiency of the LED. In addition, the lattice mismatch and low miscibility between InN and GaN are serious, and In clusters are likely to appear in the InGaN / GaN active region, resulting in phenomena such as non-uniform light emission and impure color rendering. In addition, due to its spontaneous polarization and piezoelectric polarization, group III nitrides will form a built-in electric field, which is prone to the quantum-confined Stark effect and exacerbates electron leakage.

[0044] To solve this problem, currently, it is common to insert an AlGaN electron blocking layer (EBL) between the InGaN / GaN active region and the P layer to increase the conduction band electron barrier and reduce electron leakage. However, this method also hinders the hole transfer from the P layer to the active region, thereby hindering the recombination of electrons and holes in the active region and affecting the light-emitting efficiency of the LED.

[0045] Therefore, reducing electron leakage, increasing hole injection efficiency, weakening the strong polarization electric field, and promoting the efficient recombination of carriers in the active region have become urgent problems to improve the light-emitting power of the LED.

[0046] For example, set the In composition of the InGaN / GaN active region to be constant, the thickness of the quantum barrier (QB) to be constant, and the AlGaN EBL with a high Al composition, etc.

[0047] However, when the In composition of the InGaN / GaN active region is set to be constant, the lattice mismatch is large, the polarization electric field is strong, and in the InGaN material with a high In composition, its crystal quality will be worse, affecting the light-emitting efficiency of the LED; for the AlGaN EBL with a high Al composition, while increasing the electron blocking, it also increases the barrier for holes in the valence band, affecting the recombination of electrons and holes. And there is a large lattice mismatch between the last quantum barrier (LQB) and the AlGaN EBL, and a polarization electric field will be formed at the interface, weakening its ability to block electrons.

[0048] In view of this, the present invention provides an LED epitaxial structure for improving luminous efficiency and a manufacturing method thereof. Through the Cap layer design of GaN + AlInGaN and the growth mode with a gradual change in the Al-to-In ratio, it can not only achieve polarization matching but also form a high conduction band barrier to reduce electron leakage. Moreover, in the initial stage of the growth of the quantum well, a growth mode with pre-injection of In is adopted to form InN clusters, increasing the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence. At the same time, the quantum barrier adopts a growth mode with a gradual change in thickness, and the quantum well adopts a growth mode with a gradual change in In composition, which can reduce the lattice mismatch between materials, weaken the strong polarization electric field, and improve the luminous efficiency of the LED.

[0049] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] In the present invention, the equipment used is MOCVD (Metal Organic Chemical Vapor Deposition). Trimethylgallium (TMGa) / Triethylgallium (TEGa), Trimethylaluminum (TMAl), and ammonia (NH3) are used as the Ga source, Al source, and nitrogen source, respectively, N2 is used as the carrier gas, and the N-type doping source and P-type doping source are silane (SiH4) and bis(cyclopentadienyl)magnesium (CP2Mg), respectively.

[0051] Reference Figures 1 - 3 , Figure 1 is a schematic diagram of an LED epitaxial structure for improving luminous efficiency provided by an embodiment of the present invention, Figure 2 is a schematic diagram of another LED epitaxial structure for improving luminous efficiency provided by an embodiment of the present invention, Figure 3 is a schematic diagram of the conduction band of a MQW provided by an embodiment of the present invention.

[0052] As Figures 1 - 3 shown, the LED epitaxial structure includes:

[0053] A substrate 10, and the substrate 10 can be a sapphire substrate;

[0054] And a buffer layer 12, an N-GaN layer 13, a multi-quantum well structure 15 (MQW), and a P-GaN layer 16 are sequentially grown on one side surface of the substrate 10;

[0055] Among them, the multi-quantum well structure 15 is formed by alternating multiple quantum barriers 151 and quantum wells 152. The quantum well 152 includes an InN layer 51, an InGaN layer 52, a GaN layer 53, and an AlInGaN layer 54 that are sequentially grown on the quantum barrier 151. The GaN layer 53 and the AlInGaN layer 54 constitute the Cap layer 50. Between the N-GaN layer 13 and the P-GaN layer 16, the Cap layer 50 adopts a growth method with a gradually changing Al-to-In ratio, which can achieve polarization matching, form a high conduction band barrier, and reduce electron leakage. Moreover, in the initial stage of the growth of the quantum well 152, a growth method of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

[0056] Among them, the buffer layer 12 is an undoped GaN layer with a thickness of 2.5 um to 3.5 um, such as 2.8 um.

[0057] The N-GaN layer 13 is N-type doped with a thickness of 1.3 nm to 1.8 um, such as 1.5 nm, and a doping concentration of 1 - 10x10 18 cm -3 。

[0058] The P-GaN layer 16 is P-type doped with a thickness of 100 nm to 150 nm, such as 120 nm, and a doping concentration of 5 - 10x10 18 cm -3 。

[0059] Based on Figure 1 the LED epitaxial structure shown, it further includes:

[0060] an undoped AlN low-temperature nucleation layer 11 disposed between the substrate 10 and the buffer layer 12, and the thickness of the undoped AlN low-temperature nucleation layer 11 is 10 nm to 20 nm, such as 15 nm;

[0061] a contact layer 17 disposed on the surface of the P-GaN layer 16 facing away from the multi-quantum well structure 15. The contact layer 17 can be a P-type GaN contact layer with a thickness of 10 nm to 20 nm, such as 15 nm, and a doping concentration of 1 - 5x10 19 cm -3 ;

[0062] a P electrode 18 disposed on the surface of the contact layer 17 facing away from the P-GaN layer 16;

[0063] an N electrode 14 disposed on the surface of the N-GaN layer 13 facing away from the buffer layer 12.

[0064] In the embodiment of the present invention, the growth period of the quantum barrier is N + 1, where N is 6 to 12;

[0065] The thickness of the 1st to the (N - 3)th quantum barriers is D QB1 , D QB1 = 7 to 16 nm;

[0066] The thickness of the (N - 1)th and the (N - 2)th quantum barriers is D QB2 , D QB1 -D QB2 ≥ 2 to 6 nm;

[0067] The thickness of the Nth quantum barrier is D QB3 , D QB2 -D QB3 ≤ 2 to 4 nm;

[0068] The thickness of the (N + 1)th quantum barrier (LQB) is D QB4 , D QB4 = 18 to 30 nm.

[0069] Among them, in the 1st to the (N + 1)th quantum barriers, the 1st to the Nth quantum barriers are GaN layers, and the (N + 1)th quantum barrier is an AlGaN layer.

[0070] In this solution, the thickness of the quantum barrier 151 is optimized, that is, a thick barrier is adopted before the effective light-emitting region, a thin barrier is adopted in the light-emitting region, and an even thinner barrier is adopted after the light-emitting region. The main advantage of such a design is that the first (N - 3) relatively thick quantum barriers 151 play a role in confining electrons; the (N - 1) / (N - 2) quantum barriers 151 near the P layer are thinner, which is beneficial to the transport of holes between the wells, achieving the purpose of increasing hole injection, and thus promoting the recombination of electrons and holes; finally, the thickness of the Nth quantum barrier 151 is even thinner to enhance the transport of holes from the P layer to the active region, and at the same time protect the effective light-emitting well from being damaged by the subsequent P layer temperature rise.

[0071] It should be noted that the (N + 1)th quantum barrier 151 is also specially designed. Its thickness is designed to be greater than that of the 1st to the Nth quantum barriers 151, and the (N + 1)th quantum barrier 151 adopts a graded Al design, and at the same time removes the EBL. The graded Al composition forms a polarization match between the active region and the P layer. The purpose of such a design is to make its contact interface with the Cap layer 50 and the subsequent P layer polarization-matched, suppress electron leakage, and while reducing electron leakage, increase hole injection and improve the light-emitting efficiency.

[0072] In the embodiment of the present invention, the growth period of the quantum well is N, where N is 6 to 12;

[0073] The In composition in the 1st to the (N - 4)th quantum wells is X and gradually increases, 0.05 ≤ X ≤ 0.3;

[0074] The In composition in the (N - 3)th and (N - 2)th quantum wells remains unchanged, being 0.25 - 0.3;

[0075] The In composition in the (N - 1)th and Nth quantum wells is Y, and gradually decreases, where 0.1 ≤ Y ≤ 0.2.

[0076] Each quantum well 152 includes an InN layer 51, an InGaN layer 52, a GaN layer 53, and an AlInGaN layer 54; wherein, the GaN layer 53 and the AlInGaN layer 54 constitute the Cap layer 50, and the thickness of the Cap layer 50 can be 1 - 5 nm.

[0077] In this solution, the Cap layer 50 is designed to adopt the GaN + AlInGaN, Al - ratio - In gradient mode, and the quantum well 152 is baked for a short time after growth. The purpose is to reduce In clusters. At the same time, during the growth of the Cap layer 50, the GaN layer 53 grows with variable flow rate, playing a role of quickly burying and protecting the quantum well 152; the Al - ratio - In in the AlInGaN layer 54 is graded, which not only achieves polarization matching but also can form a relatively high conduction - band barrier to reduce electron leakage.

[0078] In the embodiments of the present invention, the quantum well 152 adopts the In - gradient mode, that is, the In gradually increases before the effective light - emitting well and gradually decreases after the well, and the In composition in the light - emitting well is constant. The advantage of such a design is that the In composition in the first (N - 4) quantum wells 152 gradually increases to make the stress between layers a gradually increasing process rather than a sudden change process, playing a buffering role and reducing the strong polarization field generated by the sudden change of stress; the In composition in the (N - 3) / (N - 2)th quantum wells 152 remains unchanged to stabilize the light emission, with higher color purity. At the same time, the number of light - emitting wells is small, and the peak efficiency shifts towards the small - current direction, which is more conducive to improving the light - emitting efficiency of small - size chips; the In composition in the last (N - 1) / Nth quantum wells 152 gradually decreases to better connect with the P layer, reduce the lattice mismatch, and at the same time protect the effective well from being damaged by the subsequent P - layer temperature rise.

[0079] Moreover, the pre - passing - In growth mode before the above - mentioned quantum well 152 also has the following advantages: 1. The InN layer 51 formed by pre - passing In is relatively thin and mainly exists in the form of InN clusters. These clusters provide seeds for the InGaN layer 52 in the subsequent quantum well 152, thus promoting the incorporation of In in the quantum well 152 and forming In - rich quantum dots, which is beneficial to radiative recombination and light emission; 2. Reduce the leakage channels formed by threading dislocations (In atoms can pin at the bottom of dislocations, prevent the continuous climb of dislocations during the growth process, increase the incorporation of In, reduce the dislocation density, and thus reduce the leakage channels).

[0080] In the present solution, for the quantum well 152 with gradually changing In as compared with the constant In, the strong polarization electric field caused by the stress mutation is reduced, and at the same time, effective connection (composition and lattice) can be achieved with both the N / P layers; the thin barrier design of the effective light-emitting region is conducive to the inter-well transfer of carriers, and the thick barrier near the N layer and the thin barrier near the P layer serve to increase the electron confinement and hole injection. The pre-pass In growth before the quantum well 152 not only reduces the dislocation density in the subsequent MQW growth but also increases the radiative recombination power. The baking and optimized growth before the Cap layer 50 reduce In clusters, improve the crystal quality between the well and the barrier, reduce electron leakage, and enhance the effective recombination. The gradually changing Al in the LQB and the removal of the EBL are also for polarization matching and the purpose of increasing hole injection.

[0081] As can be seen from the above description, in the LED epitaxial structure for improving the luminous efficiency provided by the technical solution of the present invention, the Cap layer design of GaN + AlInGaN and the growth method with gradually changing Al ratio to In can not only achieve polarization matching but also form a high conduction band barrier and reduce electron leakage.

[0082] Moreover, in the initial stage of the growth of the quantum well, the growth method of pre-passing In is adopted to form InN clusters and increase the incorporation of In, thereby reducing the threading dislocations and increasing the radiative recombination luminescence.

[0083] At the same time, the quantum barrier adopts a growth method with gradually changing thickness, and the quantum well adopts a growth method with gradually changing In composition, which can reduce the lattice mismatch between materials, weaken the strong polarization electric field, and improve the luminous efficiency of the LED.

[0084] Based on the above embodiments, another embodiment of the present invention further provides a manufacturing method for an LED epitaxial structure for improving the luminous efficiency, as Figures 1 - 12 shown, Figure 4 is a schematic diagram of the growth source for a multi-quantum well structure provided by an embodiment of the present invention, Figures 5 - 12 is a process flow chart of a manufacturing method for an LED epitaxial structure for improving the luminous efficiency provided by an embodiment of the present invention.

[0085] As Figures 1 - 12 shown, the manufacturing method includes:

[0086] Step S11: As Figure 5 shown, provide a substrate 10, and the substrate 10 can be a sapphire substrate;

[0087] Step S12: As Figures 6 - 12 shown, grow an undoped AlN low-temperature nucleation layer 11, a buffer layer 12, an N-GaN layer 13, a multi-quantum well structure 15, a P-GaN layer 16, a contact layer 17, and a P electrode 18 and an N electrode 14 in sequence on one side surface of the substrate 10.

[0088] Among them, the multi-quantum well structure 15 is formed by alternating multiple quantum barriers 151 and quantum wells 152. The quantum well 152 includes an InN layer 51, an InGaN layer 52, a GaN layer 53, and an AlInGaN layer 54 that are sequentially grown on the quantum barrier 151. The GaN layer 53 and the AlInGaN layer 54 constitute the Cap layer 50. Between the N-GaN layer 13 and the P-GaN layer 16, the Cap layer 50 adopts a growth method with a gradually changing Al ratio to In ratio, which can achieve polarization matching, form a high conduction band barrier, and reduce electron leakage. Moreover, in the initial stage of the growth of the quantum well 152, a growth method of pre-passing In is adopted to form InN clusters, increasing the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

[0089] In step S12, first place the sapphire substrate into the MOCVD reaction chamber, set the temperature to 1100 °C, introduce high-purity hydrogen H for 5 - 10 min, then cool down to 950 °C - 970 °C, and finally introduce the Al source and the N source to grow an undoped AlN low-temperature nucleation layer 11 with a thickness of 10 nm - 20 nm on the sapphire substrate, as Figure 6 shown.

[0090] Furthermore, as Figure 7 shown, after growing the undoped AlN low-temperature nucleation layer 11, the temperature can be further increased to 1000 °C - 1150 °C, then the Al source is turned off, and TMGa source is introduced to grow a buffer layer 12 with a thickness of 2.5 μm - 3.5 μm on the surface of the undoped AlN low-temperature nucleation layer 11 facing away from the sapphire substrate. The buffer layer 12 is an undoped GaN layer, and the purpose is to reduce the lattice mismatch between the sapphire substrate and the subsequent grown materials by growing a high-quality GaN layer.

[0091] Furthermore, as Figure 8 shown, after growing the buffer layer 12, silane can be continuously introduced to grow a patterned N-GaN layer 13 with a thickness of 1.3 μm - 1.8 μm on the surface of the buffer layer 12 facing away from the undoped AlN low-temperature nucleation layer 11. The doping concentration of Si is 1 - 10x10 18 cm -3 .

[0092] Furthermore, as Figure 9 shown, an N electrode 14 is formed on one side of the patterned N-GaN layer.

[0093] Furthermore, as Figure 2 , Figure 4 and Figure 10As shown, a multi - quantum well structure 15 is grown on the surface of the side of the N - GaN layer 13 facing away from the buffer layer 12; the multi - quantum well structure 15 is formed by alternating multiple quantum barriers 151 and quantum wells 152; the quantum barrier 151 includes a GaN layer or an AlGaN layer, and the quantum well 152 includes an InN layer 51, an InGaN layer 52, a GaN layer 53, and an AlInGaN layer 54, and the GaN layer 53 and the AlInGaN layer 54 constitute a Cap layer 50.

[0094] In an embodiment of the present invention, taking one period of the multi - quantum well structure 15 as an example for description, as Figure 2 and Figure 4 shown, its specific growth process includes:

[0095] 1. First, a Ga source is introduced, and a GaN layer 151 with a thickness of 7 nm to 16 nm is grown on the surface of the side of the N - GaN layer 13 facing away from the buffer layer 12.

[0096] 2. Then, the temperature starts to decrease, and an InN layer 51 is grown on the surface of the side of the GaN layer 151 facing away from the N - GaN layer 13. The temperature - decreasing time is t0 + t1 + t2, and the pre - passing In growth method is adopted. That is, within the t0 time of temperature decrease, the source is turned off to allow sufficient time for the gas flow / source in the cavity to switch. In is passed alone within the t1 time. The In source is turned off within the t2 time, and NH3 is introduced to prevent the InN layer grown in the t1 time from desorbing (NH3 provides a high V / III ratio to inhibit In desorption). Preferably, the amount of In passed within the t1 time gradually decreases because as the temperature decreases, the incorporation of In increases, and the gradual decrease in the amount of In passed can make the distribution of In in the entire InN layer 51 more uniform.

[0097] 3. Then, an In source is introduced again, and an InGaN layer 52 with a thickness of 1 nm to 5 nm is grown on the surface of the side of the InN layer 51 facing away from the GaN quantum barrier layer 151 (time t3).

[0098] 4. Then, the In source / Ga source is turned off for t4 (t4 is 1 s to 5 s, short - time baking), and then a Ga source is introduced, and a GaN layer 53 is grown on the surface of the side of the InGaN layer 52 facing away from the InN layer 51 (time t5).

[0099] 5. Then, an In source / Al source is introduced, and an AlInGaN layer 54 is grown on the surface of the side of the GaN layer 53 facing away from the InGaN layer 52 (time t6). Among them, the GaN layer 53 and the AlInGaN layer 54 constitute a Cap layer 50, and the overall thickness can be 1 to 5 nm.

[0100] Among them, the Cap layer 50 is designed with GaN + AlInGaN, and the Al ratio to In is in a gradual change manner. And the quantum well 152 is baked for a short time after growth to reduce In clusters. At the same time, during the growth of the Cap layer 50, the GaN layer 53 has a variable flow rate growth, which plays a role in quickly burying and protecting the quantum well 152; in the AlInGaN layer 54, the Al ratio to In is in a gradual change, which not only achieves polarization matching but also forms a relatively high conduction band barrier to reduce electron leakage.

[0101] 6. Finally, keep the flow rate of the Ga source unchanged, then gradually increase the flow rate of the Al source until it reaches a certain value and then gradually decrease it. On the surface of the AlInGaN layer 54 facing away from the GaN layer 53, grow the last layer of AlGaN quantum barrier layer (LQB), and its thickness can be 18 nm to 30 nm. The purpose of such a design is to make the polarization matching at the contact interfaces with the Cap layer 50 and the subsequent P layer, and suppress electron leakage.

[0102] Moreover, the last layer of AlGaN quantum barrier layer adopts a gradual Al design, and at the same time, the EBL is removed. The gradual Al composition forms polarization matching between the active region and the P layer. At the same time, while reducing electron leakage, removing the EBL increases the injection of holes and improves the light emission efficiency.

[0103] Furthermore, as Figure 11 shown, after growing the last layer of AlGaN quantum barrier layer, continue to adjust the temperature to 900 - 1000 °C, and introduce TMGa source, nitrogen source, and magnesium cyclopentadienyl. On the surface of the AlGaN quantum barrier layer facing away from the AlInGaN layer 54, grow the P-GaN layer 16, and its thickness can be 100 - 150 nm, and the doping concentration is 5 - 10x10 18 cm -3 .

[0104] Furthermore, as Figure 12 shown, on the surface of the P-GaN layer 16 facing away from the multi-quantum well structure 15, grow a thin P-type GaN contact layer 17, and its thickness can be 10 - 20 nm, and the doping concentration is 1 - 5x10 19 cm -3 , and it needs to be annealed in an N2 atmosphere at 850 - 900 °C for 20 - 30 minutes.

[0105] Finally, as Figure 1 shown, on the surface of the contact layer 17 facing away from the multi-quantum well structure 15, grow the P electrode 18.

[0106] It should be noted that the pressure for the entire reaction growth is 100 - 300 torr.

[0107] In the above-mentioned multi-quantum well structure 15, the period of the quantum well 152 is N, and N is 6 - 12;

[0108] Among them, the In composition in the 1st to the (N - 4)th quantum wells is X and gradually increases, where 0.05 ≤ X ≤ 0.3; the In composition in the (N - 3)th and (N - 2)th quantum wells remains unchanged, being 0.25 - 0.3; the In composition in the (N - 1)th and Nth quantum wells is Y and gradually decreases, where 0.1 ≤ Y ≤ 0.2.

[0109] The In composition in the quantum well 152 adopts a gradual change in In, that is, the In composition gradually increases before the effective light-emitting well and gradually decreases after the well, and the In composition in the light-emitting well is constant. The advantage of such a design is that the gradual increase in the In composition in the first (N - 4) quantum wells is to make the stress between layers a gradually increasing process rather than a sudden change process, playing a buffering role and reducing the strong polarization field generated by the sudden change of stress; the constant In composition in the (N - 3) / (N - 2) quantum wells is to stabilize the light emission with higher color purity. At the same time, the number of light-emitting wells is small, and the peak efficiency shifts towards the small-current direction, which is more conducive to improving the light-emitting efficiency of small-size chips; the gradual decrease in the In composition in the last (N - 1) / N quantum wells is to better connect with the P layer, reduce the lattice mismatch, and at the same time protect the effective well from being damaged by the subsequent P layer heating.

[0110] Moreover, pre-passivating In growth is adopted in front of the quantum well. By using the formed InN clusters, the incorporation of In is increased to achieve the purpose of reducing threading dislocations and increasing radiative recombination luminescence.

[0111] In the embodiment of the present invention, the gradually changing In in the quantum well, compared with the constant In, reduces the strong polarization electric field caused by stress mutation, and at the same time can effectively connect with both the N / P layers (composition, lattice); the thin barrier design in the effective light-emitting region is conducive to the inter-well transport of carriers, and the thick barrier near the N layer and the thin barrier near the P layer serve the purpose of increasing electron confinement and hole injection. The pre-passivating In growth in front of the quantum well not only reduces the dislocation density in the subsequent MQW growth but also increases the radiative recombination power. The baking and optimized growth in front of the Cap layer reduce In clusters, improve the crystal quality between the well and the barrier, reduce electron leakage, and enhance effective recombination. The gradually changing Al in the LQB and the removal of the EBL are also for polarization matching and the purpose of increasing hole injection.

[0112] Moreover, the pre-passivating In growth method adopted in front of the above-mentioned quantum well has the following advantages: 1. The InN layer formed by pre-passivating In is relatively thin and mainly exists in the form of InN clusters. These clusters provide seeds for InGaN in the subsequent quantum wells, thus promoting the incorporation of In in the quantum wells to form In-rich quantum dots, which is beneficial to radiative recombination luminescence; 2. It reduces the leakage channels formed by threading dislocations (In atoms can pin at the bottom of the dislocations, preventing the continuous climb of dislocations during the growth process. Increasing the incorporation of In can reduce the dislocation density and thus reduce the leakage channels).

[0113] In the above-mentioned multi-quantum well structure 15, the period of the quantum barrier 151 is N + 1, where N ranges from 6 to 12;

[0114] Among them, the thickness of the 1st to the (N - 3)th quantum barriers is D QB1 , D QB1 = 7 to 16 nm; the thickness of the (N - 1)th and (N - 2)th quantum barriers is D QB2 , D QB1 - D QB2 ≥ 2 to 6 nm; the thickness of the Nth quantum barrier is D QB3 , D QB2 - D QB3 ≤ 2 to 4 nm; the thickness of the (N + 1)th quantum barrier is D QB4 , D QB4 = 18 to 30 nm.

[0115] In this solution, the thickness of the quantum barrier 151 is optimized, that is, a thick barrier is used in front of the effective light-emitting region, a thin barrier in the light-emitting region, and an even thinner barrier behind the light-emitting region. The main advantage of this design is that the first (N - 3) relatively thick quantum barriers play a role in confining electrons; the (N - 1) / (N - 2) quantum barriers near the P layer are thinner, which is beneficial for the hole to transport between the wells, achieving the purpose of increasing hole injection, and thus promoting the recombination of electrons and holes; finally, the Nth quantum barrier layer is even thinner to enhance the transport of holes from the P layer to the active region, and at the same time protect the effective light-emitting wells from being damaged by the subsequent P layer temperature rise; the last quantum barrier is also specially designed, and its thickness is greater than that of the 1st to the Nth quantum barriers. The purpose of this design is to make the polarization match at the contact interface with the Cap layer and the subsequent P layer, and suppress electron leakage.

[0116] Through the above description, it can be seen that in the manufacturing method of the LED epitaxial structure for improving the luminous efficiency provided by the technical solution of the present invention, the Cap layer design of GaN + AlInGaN and the growth mode of gradually changing the Al ratio to In can not only achieve polarization matching, but also form a high conduction band barrier and reduce the effect of electron leakage.

[0117] Moreover, in the initial stage of the growth of the quantum well, the growth mode of pre-passing In is adopted to form InN clusters and increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

[0118] At the same time, the quantum barrier adopts a growth mode of gradually changing the thickness, and the quantum well adopts a growth mode of gradually changing the In composition, which can reduce the lattice mismatch between materials, weaken the strong polarization electric field, and improve the luminous efficiency of the LED.

[0119] In this specification, each embodiment is described in a progressive, or parallel, or a combination of progressive and parallel ways. The key point of each embodiment is to illustrate the differences from other embodiments. For the same and similar parts between each embodiment, reference can be made to each other.

[0120] It should be noted that, in this document, relational 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 any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that an article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the article or device comprising the above element.

[0121] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious 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 is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An LED epitaxial structure for improving luminous efficiency, characterized in that Comprising: a substrate, and a buffer layer, an N-GaN layer, a multi-quantum well structure, and a P-GaN layer sequentially grown on one surface of the substrate; wherein, the multi-quantum well structure is formed by alternating multiple quantum barriers and quantum wells, the quantum well includes an InN layer, an InGaN layer, a GaN layer, and an AlInGaN layer sequentially grown on the quantum barrier, the GaN layer and the AlInGaN layer constitute a Cap layer, and between the N-GaN layer and the P-GaN layer, the Cap layer adopts a growth mode with a gradually changing Al to In ratio, which can play a role in polarization matching, form a high conduction band barrier, and reduce electron leakage, and in the initial stage of the growth of the quantum well, a growth mode of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

2. The LED epitaxial structure according to claim 1, wherein, The growth period of the quantum barrier is N + 1, where N is 6 to 12; The thickness of the 1st to the (N - 3)th quantum barrier is D QB1 , D QB1 = 7 to 16 nm; The thicknesses of the (N - 1)-th and (N - 2)-th quantum barriers are D QB2 , D QB1 -D QB2 ≥2 to 6 nm; The thickness of the Nth quantum barrier is D QB3 , D QB2 -D QB3 ≤ 2 - 4 nm; The thickness of the (N + 1)-th quantum barrier is D QB4 , D QB4 = 18~30 nm.

3. The LED epitaxial structure according to claim 2, characterized in that, The first to the Nth quantum barriers are all GaN layers, and the (N + 1)th quantum barrier is an AlGaN layer.

4. The LED epitaxial structure according to claim 1, wherein, The growth period of the quantum well is N, where N is 6 to 12; In the first to the (N - 4)th quantum wells, the In component is X and gradually increases, 0.05 ≤ X ≤ 0.3; In the (N - 3)th and (N - 2)th quantum wells, the In component remains unchanged, being 0.25 to 0.3; In the (N - 1)th and Nth quantum wells, the In component is Y and gradually decreases, 0.1 ≤ Y ≤ 0.

2.

5. The LED epitaxial structure according to claim 1, wherein The thickness of the Cap layer is 1 to 5 nm.

6. The LED epitaxial structure according to claim 1, characterized in that, Further comprising: an undoped AlN low-temperature nucleation layer disposed between the substrate and the buffer layer; a contact layer disposed on the surface of the P-GaN layer facing away from the multi-quantum well structure; a P electrode disposed on the surface of the contact layer facing away from the P-GaN layer; an N electrode disposed on the surface of the N-GaN layer facing away from the buffer layer.

7. The LED epitaxial structure according to claim 1, wherein The thickness of the N-GaN layer is 1.3~1.8 μm, and the doping concentration is 1-10x10 18 cm -3 .

8. The LED epitaxial structure according to claim 1, wherein The thickness of the P-GaN layer is 100~150 nm, and the doping concentration is 5-10x10 18 cm -3 .

9. The LED epitaxial structure according to claim 1, characterized in that, The substrate is a sapphire substrate.

10. A method for fabricating an LED epitaxial structure with improved luminous efficiency, characterized in that, The manufacturing method includes: providing a substrate; sequentially growing a buffer layer, an N-GaN layer, a multi-quantum well structure, and a P-GaN layer on one surface of the substrate; wherein, the multi-quantum well structure is formed by alternating multiple quantum barriers and quantum wells, the quantum well includes an InN layer, an InGaN layer, a GaN layer, and an AlInGaN layer sequentially grown on the quantum barrier, the GaN layer and the AlInGaN layer constitute a Cap layer, and between the N-GaN layer and the P-GaN layer, the Cap layer adopts a growth mode with a gradually changing Al to In ratio, which can play a role in polarization matching, form a high conduction band barrier, and reduce electron leakage, and in the initial stage of the growth of the quantum well, a growth mode of pre-passing In is adopted to form InN clusters, increase the incorporation of In, thereby reducing threading dislocations and increasing radiative recombination luminescence.

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