LED epitaxial structure and forming method thereof, LED chip

Abstract

This application relates to the field of semiconductor optoelectronic device technology, specifically to an LED epitaxial structure and its formation method, and an LED chip. The LED epitaxial structure includes: a semiconductor substrate; an n-type GaN layer close to the semiconductor substrate; a p-type GaN layer away from the semiconductor substrate; a multi-quantum-well layer located between the n-type GaN layer and the p-type GaN layer; and a first stress-relieving layer located between the multi-quantum-well layer and the n-type GaN layer. The first stress-relieving layer is a superlattice layer formed by stacking multiple repeatedly stacked first basic units. Each first basic unit includes an InGaN layer and a GaN layer on top of the InGaN layer. The In content in the first basic unit gradually increases from the n-type GaN layer to the p-type GaN layer. The LED epitaxial structure of this application can effectively reduce the lattice mismatch of InGaN-based LED epitaxial structures and improve device efficiency.

Description

Technical Field

[0001] This application relates to the field of semiconductor optoelectronic device technology, specifically to an LED epitaxial structure and its formation method, and an LED chip. Background Technology

[0002] With the widespread application of micro-display technology in augmented reality (AR), virtual reality (VR), and wearable devices, the demand for high-brightness, high-resolution, and high-color-purity full-color LED displays is increasing. InGaN is the core active layer material for fabricating blue, green, and white LEDs. By increasing the indium content in the active region of InGaN, its emission wavelength can be extended to longer wavelengths (such as green, yellow, and red light). However, there are two major technical bottlenecks in growing high-indium-content InGaN: 1) There is a severe lattice mismatch between high-indium-content InGaN and the underlying GaN or low-indium-content InGaN, which generates significant stress. This stress easily induces film cracking, high-density dislocations, and V-shaped pits, severely degrading crystal quality and device performance. 2) Growing high-indium-content InGaN requires relatively low temperatures to suppress indium desorption, but at low temperatures, the mobility of Ga atoms decreases, which may lead to a decrease in crystal quality and the formation of non-radiative recombination centers, resulting in a lower-than-ideal electro-optical conversion efficiency of the device.

[0003] Traditional solutions include using stepped temperature growth and inserting low-temperature buffer layers. However, these methods often lack fine-grained control over long-wavelength stress or introduce additional interface problems, resulting in unsatisfactory crystal quality and luminous efficiency of the active quantum well.

[0004] Therefore, a solution is needed to address the problems of severe lattice mismatch in InGaN-based LED epitaxial structures, the formation of non-radiative recombination centers during growth, and unsatisfactory device efficiency. Summary of the Invention

[0005] This application provides an epitaxial structure for LED epitaxy, a method for forming the same, and an LED chip, to solve the problems of severe lattice mismatch, formation of non-radiative recombination centers during the growth process, and unsatisfactory device efficiency in InGaN-based LED epitaxial structures.

[0006] In one aspect of this application, an LED epitaxial structure includes: a semiconductor substrate; an n-type GaN layer close to the semiconductor substrate; a p-type GaN layer away from the semiconductor substrate; a multi-quantum well layer located between the n-type GaN layer and the p-type GaN layer; a first stress relief layer located between the multi-quantum well layer and the n-type GaN layer; the first stress relief layer is a superlattice layer formed by stacking a plurality of repeatedly stacked first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; the In content in the first basic unit gradually increases in the direction from the n-type GaN layer to the p-type GaN layer.

[0007] The LED epitaxial structure provided in this application utilizes a superlattice layer with gradually increasing In content as a first stress buffer layer between a multi-quantum-well layer and an n-type GaN layer. This transforms the significant lattice mismatch caused by the large difference in In content between the multi-quantum-well bottom layer and the n-type GaN layer into a layer-by-layer stress release caused by the gradual increase in In content across multiple superlattice layers. This shifts stress release from a single interface to a multi-interface process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. Furthermore, because the In content gradually increases in the first stress buffer layer, growth begins with layers with lower In content. The lower In composition of the initial layer provides a better crystal template for the subsequent growth of higher In content layers, improving surface morphology and facilitating more effective incorporation and more uniform distribution of In atoms in subsequent high-In layers. Simultaneously, the multiple interfaces of the superlattice layer can effectively bend, block, or annihilate penetrating dislocations extending from the lower layers, preventing them from entering the multi-quantum-well layer and significantly reducing the non-radiative recombination center density of the multi-quantum-well layer. Based on the above, the overall crystal quality of the epitaxial structure is improved, the stress environment is optimized, and the radiative recombination efficiency of the multi-quantum-well active region is significantly enhanced. In particular, for long-wavelength LEDs, the internal quantum efficiency and optical output power can be substantially improved. Furthermore, the LED epitaxial structure of this embodiment can be fully realized using conventional group III nitride growth processes such as MOCVD, without the need for complex patterned substrates or bonding techniques, making it easy to industrialize and promote.

[0008] In some embodiments of this application, the In content in different first basic units increases linearly along the direction from the n-type GaN layer to the p-type GaN layer.

[0009] In some embodiments of this application, all first basic units are divided into several groups, and the In content in the first basic units of different groups gradually increases along the direction from the n-type GaN layer to the p-type GaN layer, and the In content in the first basic units of the same group is the same.

[0010] In some embodiments of this application, the LED epitaxial structure further includes: a second stress relief layer located between the multi-quantum-well layer and the p-type GaN layer; the second stress relief layer is a superlattice layer formed by stacking multiple repeating second basic units; each second basic unit includes an InGaN layer and a GaN layer on the InGaN layer; the In content in the second basic unit gradually decreases in the direction from the n-type GaN layer to the p-type GaN layer.

[0011] In some embodiments of this application, the In content in the first basic unit of different groups decreases linearly along the direction from the n-type GaN layer to the p-type GaN layer.

[0012] In some embodiments of this application, all second basic units are divided into several groups, and the In content in the second basic units of different groups gradually decreases along the direction from the n-type GaN layer to the p-type GaN layer, while the In content in the second basic units of the same group is the same.

[0013] In some embodiments of this application, the LED epitaxial structure further includes: a nucleation layer located on the surface of a semiconductor substrate; the nucleation layer is a GaN layer; a buffer layer, which is an undoped GaN layer or an AlGaN layer, is located on the surface of the nucleation layer; an n-type GaN layer is located on the surface of the buffer layer; the semiconductor substrate is a sapphire substrate, a Si substrate, or a SiC substrate; the n-type GaN layer is a Si-doped GaN layer; wherein the Si doping concentration is 1×10⁻⁶. 18 cm -3 ~5×10 19 cm -3 The multi-quantum-well layer consists of alternating stacks of multiple repetitive quantum well layers and quantum barrier layers; the quantum well layers are InGaN layers, and the quantum barrier layers are GaN layers or InGaN layers; the p-type GaN layer is a Mg-doped GaN layer; wherein the Mg doping concentration is 5 × 10⁻⁶. 18 cm -3 ~5×10 20 cm -3 The LED epitaxial structure also includes: an electron blocking layer located between the multi-quantum-well layer and the p-type GaN layer; the electron blocking layer is a Mg-doped AlGaN layer; and an ohmic contact layer located on the surface of the p-type GaN layer away from the multi-quantum-well layer.

[0014] In some embodiments of this application, in the first stress relief layer, along the direction from the n-type GaN layer to the p-type GaN layer, the In content gradually increases from 30% of the In content on the side of the multi-quantum well layer near the n-type GaN layer to 70% of the In content on the side of the multi-quantum well layer near the n-type GaN layer; in the second stress relief layer, along the direction from the n-type GaN layer to the p-type GaN layer, the In content gradually decreases from 70% of the In content on the side of the multi-quantum well layer near the p-type GaN layer to 30% of the In content on the side of the multi-quantum well layer near the p-type GaN layer; the number of second basic units is 3 to 15; in the multi-quantum well layer, the thickness of the quantum well layer is 2 nm to 4 nm, and the thickness of the quantum barrier layer is 5 nm to 20 nm; the In content in the quantum well layer is 10%. The thickness of the nucleation layer is 2nm to 5nm; the thickness of the buffer layer is 2μm to 5μm; the thickness of the n-type GaN layer is 1μm to 4μm; the thickness of the p-type GaN layer is 5nm to 30nm; the thickness of the InGaN layer in the superlattice layer of the first stress relief layer is 10nm to 30nm, and the thickness of the GaN layer is 5nm to 15nm; the In content of the InGaN layer in the first stress relief layer is 2% to 12%; the thickness of the InGaN layer in the superlattice layer of the second stress relief layer is 10nm to 30nm, and the thickness of the GaN layer is 5nm to 15nm; the In content of the InGaN layer in the second stress relief layer is 2% to 12%; the thickness of the electron blocking layer is 5nm to 30nm.

[0015] In another aspect of this application, a method for forming an LED epitaxial structure is also provided, comprising the following steps: providing a semiconductor substrate; forming an n-type GaN layer close to the semiconductor substrate; forming a multi-quantum well layer on the side of the n-type GaN layer away from the semiconductor substrate; forming a p-type GaN layer on the side of the multi-quantum well layer away from the semiconductor substrate; wherein, before forming the multi-quantum well layer, the method further comprises: forming a first stress relief layer on the side of the n-type GaN layer away from the semiconductor substrate; the multi-quantum well layer is formed on the side of the first stress relief layer away from the semiconductor substrate; the first stress relief layer is a superlattice layer formed by stacking a plurality of repeatedly stacked first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; the In content in the first basic unit gradually increases in the direction from the n-type GaN layer to the p-type GaN layer.

[0016] The method for forming the LED epitaxial structure provided in this application is suitable for forming the LED epitaxial structure provided in this application. By setting a superlattice layer with gradually increasing In content between the multi-quantum well layer and the n-type GaN layer as a first stress buffer layer, the huge lattice mismatch caused by the huge difference in In content between the multi-quantum well bottom layer and the n-type GaN layer is transformed into a layer-by-layer release of stress by the multi-layer superlattice layer with gradually varying In content. This changes the stress release from a single interface to a multi-interface gradual process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. Furthermore, since the In content in the first stress buffer layer gradually increases, the growth process starts with the layer with lower In content. In particular, the lower In composition of the initial layer provides a better crystal template for the subsequent growth of higher In content, improving the surface morphology and facilitating more effective incorporation and more uniform distribution of In atoms in the subsequent high In content layers. At the same time, the multiple interfaces of the superlattice layer can effectively bend, block, or annihilate penetrating dislocations extending from the lower layer, preventing them from entering the multi-quantum well layer, thereby significantly reducing the non-radiative recombination center density of the multi-quantum well layer. Based on the above, the overall crystal quality of the epitaxial structure is improved, the stress environment is optimized, and the radiative recombination efficiency of the multi-quantum-well active region is significantly enhanced. In particular, for long-wavelength LEDs, the internal quantum efficiency and optical output power can be substantially improved. Furthermore, the LED epitaxial structure of this embodiment can be fully realized using conventional group III nitride growth processes such as MOCVD, without the need for complex patterned substrates or bonding techniques, making it easy to industrialize and promote.

[0017] In some embodiments of this application, in the step of forming the basic unit, an InGaN layer is first grown in an NH3 atmosphere, annealed, and then the temperature is maintained. The growth material is stopped, and only an NH3 atmosphere is introduced for surface reconstruction. Then the temperature is raised to grow a GaN layer. The surface reconstruction process takes 5s to 100s.

[0018] In another aspect of this application, an LED chip is also provided, including the LED epitaxial structure provided in this application.

[0019] The LED chip provided in this application, including the LED epitaxial structure, uses a superlattice layer with gradually increasing In content as a first stress buffer layer between a multi-quantum well layer and an n-type GaN layer. This transforms the significant lattice mismatch caused by the large difference in In content between the multi-quantum well bottom layer and the n-type GaN layer into a layer-by-layer release of stress through multiple superlattice layers with gradually varying In content. This changes the stress release from a single interface to a multi-interface gradual process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. Furthermore, because the In content in the first stress buffer layer gradually increases, the growth process begins with layers with lower In content. In particular, the lower In composition of the initial layer provides a better crystal template for the subsequent growth of higher In content layers, improving the surface morphology and facilitating more effective incorporation and more uniform distribution of In atoms in subsequent high-In layers. Simultaneously, the multiple interfaces of the superlattice layer can effectively bend, block, or annihilate penetrating dislocations extending from the lower layers, preventing them from entering the multi-quantum well layer, thereby significantly reducing the non-radiative recombination center density of the multi-quantum well layer. Based on the above, the overall crystal quality of the epitaxial structure is improved, the stress environment is optimized, and the radiative recombination efficiency of the multi-quantum-well active region is significantly enhanced. In particular, for long-wavelength LEDs, the internal quantum efficiency and optical output power can be substantially improved. Furthermore, the LED epitaxial structure of this embodiment can be fully realized using conventional group III nitride growth processes such as MOCVD, without the need for complex patterned substrates or bonding techniques, making it easy to industrialize and promote. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of an LED epitaxial structure according to an embodiment of this application;

[0022] Figure 2 This is a schematic diagram illustrating the change in In component content in the first stress relief layer of an LED epitaxial structure according to an embodiment of this application. Figure 3 This is a schematic diagram of the structure of the first stress relief layer in another case of the LED epitaxial structure according to an embodiment of this application; Figure 4 This is a schematic diagram illustrating the change in In component content in the first stress relief layer in another case of an LED epitaxial structure according to an embodiment of this application. Figure 5This is a comparison diagram of the device efficiency curves of an LED epitaxial structure according to an embodiment of this application and the LED epitaxial structure of Comparative Example 1; Figure 6 This is a schematic diagram of the main steps in the method for forming the LED epitaxial structure of this application; Figure 7a Electron micrograph of the surface of the stress relief layer in a method for forming an LED epitaxial structure; Figure 7b This is an electron microscope image of the stress relief layer surface in a method for forming an LED epitaxial structure according to an embodiment of this application. Detailed Implementation

[0023] As mentioned earlier, in LED chips, the InGaN-based LED epitaxial structure suffers from severe lattice mismatch, and non-radiative recombination centers are formed during the growth process, resulting in unsatisfactory device efficiency.

[0024] In view of this, this application provides an LED epitaxial structure and its formation method, as well as an LED chip, to solve the problems of severe lattice mismatch in InGaN-based LED epitaxial structures, the formation of non-radiative recombination centers during the growth process, and unsatisfactory device efficiency.

[0025] This application provides an LED epitaxial structure, comprising: a semiconductor substrate; an n-type GaN layer close to the semiconductor substrate; a p-type GaN layer away from the semiconductor substrate; a multi-quantum well layer located between the n-type GaN layer and the p-type GaN layer; a first stress relief layer located between the multi-quantum well layer and the n-type GaN layer; the first stress relief layer is a superlattice layer formed by stacking multiple repeatedly stacked first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; the In content in the first basic unit gradually increases in the direction from the n-type GaN layer to the p-type GaN layer.

[0026] This application also provides a method for forming an LED epitaxial structure, comprising the following steps: providing a semiconductor substrate; forming an n-type GaN layer close to the semiconductor substrate; forming a multi-quantum well layer on the side of the n-type GaN layer away from the semiconductor substrate; forming a p-type GaN layer on the side of the multi-quantum well layer away from the semiconductor substrate; wherein, before forming the multi-quantum well layer, the method further comprises: forming a first stress relief layer on the side of the n-type GaN layer away from the semiconductor substrate; the multi-quantum well layer is formed on the side of the first stress relief layer away from the semiconductor substrate; the first stress relief layer is a superlattice layer formed by stacking a plurality of repeatedly stacked first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; the In content in the first basic unit gradually increases in the direction from the n-type GaN layer to the p-type GaN layer.

[0027] This application also provides an LED chip, including the LED epitaxial structure provided in this application.

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Example 1 This embodiment provides an LED epitaxial structure, referenced... Figure 1 ,include: Semiconductor substrate 100; n-type GaN layer 400 close to the semiconductor substrate; p-type GaN layer 700, located away from the semiconductor substrate; A multi-quantum-well layer 600 located between an n-type GaN layer and a p-type GaN layer; The first stress relief layer 500 is located between the multi-quantum well layer 600 and the n-type GaN layer 400; The first stress relief layer 500 is a superlattice layer formed by stacking multiple repeatedly stacked first basic units; Each first basic unit includes an InGaN layer 510 and a GaN layer 520 on the InGaN layer 510; In the direction from the n-type GaN layer 400 to the p-type GaN layer 700, the In content in the first basic unit gradually increases.

[0030] by Figure 1 For example, the first stress relief layer 500 includes three first basic units, each of which includes an InGaN layer 510 and a GaN layer 520 on the InGaN layer 510. In the direction from the n-type GaN layer 400 to the p-type GaN layer 700, the three first basic units respectively include three InGaN layers 511, 512, and 513 with different In contents, wherein in each of the first basic units, the In content in the first basic unit where InGaN layer 511 is located is less than the In content in the basic unit where InGaN layer 512 is located is less than the In content in the basic unit where InGaN layer 513 is located.

[0031] It should be noted that, Figure 1 The example only uses three first basic units as an example. In practical applications, more first basic units can be stacked, not just three.

[0032] The LED epitaxial structure provided in this embodiment uses a superlattice layer with gradually increasing In content as a first stress buffer layer 500 between the multi-quantum well layer 600 and the n-type GaN layer 400. This transforms the large lattice mismatch caused by the significant difference in In content between the multi-quantum well layer 600 and the n-type GaN layer 400 into a gradual release of stress through multiple superlattice layers with gradually varying In content. This changes the stress release from a single interface to a multi-interface gradual process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. Furthermore, since the In content in the first stress buffer layer gradually increases, the growth process starts with layers with lower In content. In particular, the lower In composition of the initial layer provides a better crystal template for the subsequent growth of higher In content layers, improving the surface morphology and facilitating more effective incorporation and more uniform distribution of In atoms in the subsequent high-In layers. At the same time, the multiple interfaces of the superlattice layer can effectively bend, block, or annihilate penetrating dislocations extending from the lower layers, preventing them from entering the multi-quantum well layer, thereby significantly reducing the non-radiative recombination center density of the multi-quantum well layer. Based on the above, the overall crystal quality of the epitaxial structure is improved, the stress environment is optimized, and the radiative recombination efficiency of the multi-quantum-well active region is significantly enhanced. In particular, for long-wavelength LEDs, the internal quantum efficiency and optical output power can be substantially improved. Furthermore, the LED epitaxial structure of this embodiment can be fully realized using conventional group III nitride growth processes such as MOCVD, without the need for complex patterned substrates or bonding techniques, making it easy to industrialize and promote.

[0033] Furthermore, in some embodiments of this application, the In content in the first basic unit of different groups increases linearly along the direction from the n-type GaN layer 400 to the p-type GaN layer 700.

[0034] refer to Figure 2 The In content in the first basic unit closest to the n-type GaN layer 400 is defined as X%, and the In content in the first basic unit closest to the p-type GaN layer 700 is defined as Y%. The In content of adjacent first basic units differs by the same amount, resulting in a linear increase in In content. For example, the In content in the first basic unit is 2%, the In content in the second basic unit is 4%, the In content in the third basic unit is 6%, and so on, until the target In content is reached.

[0035] Furthermore, in some embodiments of this application, all first basic units are divided into several groups, and the In content in the first basic units of different groups gradually increases along the direction from the n-type GaN layer 400 to the p-type GaN layer 700, and the In content in the first basic units of the same group is the same.

[0036] by Figure 3For example, the first basic unit of InGaN layers 511 with the same content is the first group, which includes several InGaN layers 511 and GaN layers 520, or in other words, the basic unit of InGaN layer 511-GaN layer 520 is repeatedly stacked N1 times; the first basic unit of InGaN layers 512 with the same content is the second group, which includes several InGaN layers 512 and GaN layers 520, or in other words, the basic unit of InGaN layer 512-GaN layer 520 is repeatedly stacked N2 times; the first basic unit of InGaN layers 513 with the same content is the third group, which includes several InGaN layers 513 and GaN layers 520, or in other words, the basic unit of InGaN layer 513-GaN layer 520 is repeatedly stacked N3 times. The values ​​of N1, N2, and N3 can be the same or different. Among the three groups, the In content gradually increases in the order of the first group containing InGaN layer 511, the second group containing InGaN layer 512, and the third group containing InGaN layer 513. Within the same group, all layers have the same InGaN content, specifically InGaN layer 511, InGaN layer 512, or InGaN layer 513. The amount of InGaN added between adjacent groups can be the same or different.

[0037] Thus, for reference Figure 4 The In content of the first basic unit closest to the n-type GaN layer 400 is defined as X%, and the In content of the first basic unit closest to the p-type GaN layer 700 is defined as Y%. The In content in each group is the same, and the In content in different groups gradually increases. For example, the In content of the first basic unit in the first group is 1%, and the In content of the basic units in the same group is 1%; the In content of the first basic unit in the second group is 3%, and the In content of the basic units in the same group is 3%; the In content of the first basic unit in the third group is 7%, and the In content of the basic units in the same group is 7%... until the target In content is reached.

[0038] Furthermore, in some embodiments of this application, the LED epitaxial structure further includes: a second stress relief layer (not shown) located between the multi-quantum well layer 600 and the p-type GaN layer; the second stress relief layer is a superlattice layer formed by stacking multiple repeated stacked second basic units; each second basic unit includes an InGaN layer and a GaN layer on the InGaN layer.

[0039] Similar to the first stress-relieving layer 500, a significant lattice mismatch also exists between the multi-quantum-well layer 600 and the p-type GaN layer 700 due to the abrupt change in In content. Adding a second stress-relieving layer with gradually varying In content between them transforms the large lattice mismatch caused by the significant difference in In content between the multi-quantum-well layer 600 and the p-type GaN layer 700 (from a high In content in the multi-quantum-well layer 600 to none or extremely low In content in the p-type GaN layer 700) into a layer-by-layer stress-relieving process through multiple superlattice layers with gradually varying In content. This changes the stress release from a single interface to a multi-interface gradual process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. This further improves the overall crystal quality of the device and enhances its performance.

[0040] In some embodiments of this application, similar to the first stress-relieving layer, the In content in different second base units decreases linearly along the direction from the n-type GaN layer to the p-type GaN layer.

[0041] Alternatively, in other embodiments, all the second basic units are divided into several groups, and the In content in the second basic units of different groups gradually decreases along the direction from the n-type GaN layer to the p-type GaN layer, while the In content in the second basic units of the same group is the same.

[0042] In some embodiments of this application, the LED epitaxial structure further includes: Nucleation layer 200 is located on the surface of semiconductor substrate 100; nucleation layer 200 is a GaN layer. The buffer layer 300 is an undoped GaN layer or an AlGaN layer, located on the surface of the nucleation layer 200; the n-type GaN layer 400 is located on the surface of the buffer layer 300. Semiconductor substrate 100 is a sapphire substrate, a Si substrate, or a SiC substrate; The n-type GaN layer 400 is a Si-doped GaN layer; the Si doping concentration is 1×10⁻⁶. 18 cm -3 ~5×10 19 cm -3 ; The multi-quantum-well layer 600 is composed of multiple repetitive periodic quantum well layers and quantum barrier layers stacked alternately; the quantum well layers are InGaN layers, and the quantum barrier layers are GaN layers or InGaN layers; The p-type GaN layer 700 is a Mg-doped GaN layer; the Mg doping concentration is 5 × 10⁻⁶. 18 cm -3 ~5×10 20 cm -3 ; LED epitaxial structures also include: An electron blocking layer (not shown in the figure) is located between the multi-quantum well layer 600 and the p-type GaN layer 700; the electron blocking layer is a Mg-doped AlGaN layer. An ohmic contact layer (not shown in the figure) is located on the surface of the p-type GaN layer 700 away from the multi-quantum-well layer 600.

[0043] Furthermore, in some embodiments of this application, in the first stress relief layer 500, along the direction from the n-type GaN layer 400 to the p-type GaN layer 700, the In content gradually increases from 30% of the In content on the side of the multi-quantum well layer 600 near the n-type GaN layer to 70% of the In content on the side of the multi-quantum well layer 600 near the n-type GaN layer; the number of first basic units is 3 to 15; it should be noted that this refers to the In content in the first basic unit immediately adjacent to the multi-quantum well layer 600 being 70% of the In content of the adjacent portion of the multi-quantum well layer 600. For example, if the In content in the multi-quantum well layer 600 near this position is 10%, then the In content in the adjacent first basic unit is 7%.

[0044] In the second stress-relieving layer, along the direction from the n-type GaN layer 400 to the p-type GaN layer 700, the In content gradually decreases from 70% on the side of the multi-quantum well layer 600 near the p-type GaN layer 700 to 30% on the side of the multi-quantum well layer near the p-type GaN layer; the number of second basic units is 3 to 15; it should also be noted that this refers to the In content in the second basic unit immediately adjacent to the multi-quantum well layer 600 being 70% of the In content of the adjacent portion of the multi-quantum well layer 600. For example, if the In content in the multi-quantum well layer 600 near this position is 10%, then the In content in the adjacent second basic unit is 7%.

[0045] In the multi-quantum-well layer 600, the thickness of the quantum well layer is 2nm~4nm, and the thickness of the quantum barrier layer is 5nm~20nm; the In content in the quantum well layer is 10%~25%; The thickness of the nucleation layer 200 is 2nm~5nm; The thickness of the buffer layer 300 is 2μm~5μm; The thickness of the n-type GaN layer 400 is 1μm~4μm; The thickness of the p-type GaN layer 700 is 5nm~30nm; the thickness of the InGaN layer in the superlattice layer of the first stress relief layer is 10nm~30nm, and the thickness of the GaN layer is 5nm~15nm; The In content of the InGaN layer in the first stress relief layer 500 is 2% to 12%. It should be noted that this only limits the selectable range of the In content of the InGaN layer in the first stress relief layer, and does not mean that the In content of the InGaN layer in the first stress relief layer must increase from 2% to 12% in a certain direction.

[0046] The thickness of the InGaN layer in the superlattice layer of the second stress relief layer is 10nm~30nm, and the thickness of the GaN layer is 5nm~15nm; The In content of the InGaN layer in the second stress relief layer is 2% to 12%. It should also be noted that this only limits the selectable range of the In content of the InGaN layer in the second stress relief layer, and does not mean that the In content of the InGaN layer in the second stress relief layer must increase from 2% to 12% in a certain direction.

[0047] The thickness of the electron blocking layer is 5nm~30nm.

[0048] To verify the effectiveness of the LED epitaxial structure provided in this embodiment, Comparative Example 1 is provided, and efficiency tests are conducted under the same conditions.

[0049] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses an InGaN-based LED epitaxial structure without a superlattice layer. Comparative Example 1 does not include the first and second stress-relief layers, and Example 1 also excludes the second stress-relief layer, using only the first stress-relief layer for comparison. All other conditions are the same for Comparative Example 1 and Example 1. Results are referenced. Figure 5 :like Figure 5 As shown, under the same driving current, the luminous intensity (peak wavelength of approximately 620 nm) is increased by approximately 1.2 times; correspondingly, the light output power is also increased by approximately 1.2 times under the rated current.

[0050] Example 2 This embodiment provides a method for forming an LED epitaxial structure, referencing... Figure 6 This includes the following steps: Provide semiconductor substrates; An n-type GaN layer is formed close to the semiconductor substrate; A multi-quantum-well layer is formed on the side of the n-type GaN layer away from the semiconductor substrate; A p-type GaN layer is formed on the side of the multi-quantum-well layer away from the semiconductor substrate; Before forming the multi-quantum-well layer, the process also includes: A first stress relief layer is formed on the side of the n-type GaN layer away from the semiconductor substrate; a multiple quantum well layer is formed on the side of the first stress relief layer away from the semiconductor substrate. The first stress relief layer is a superlattice layer formed by stacking multiple repeated first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; the In content in the first basic unit gradually increases in the direction from the n-type GaN layer to the p-type GaN layer.

[0051] The method for forming the LED epitaxial structure provided in this application is suitable for forming the LED epitaxial structure provided in this application. By setting a superlattice layer with gradually increasing In content between the multi-quantum well layer and the n-type GaN layer as a first stress buffer layer, the huge lattice mismatch caused by the huge difference in In content between the multi-quantum well bottom layer and the n-type GaN layer is transformed into a layer-by-layer release of stress by the multi-layer superlattice layer with gradually varying In content. This changes the stress release from a single interface to a multi-interface gradual process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. Furthermore, since the In content in the first stress buffer layer gradually increases, the growth process starts with the layer with lower In content. In particular, the lower In composition of the initial layer provides a better crystal template for the subsequent growth of higher In content, improving the surface morphology and facilitating more effective incorporation and more uniform distribution of In atoms in the subsequent high In content layers. At the same time, the multiple interfaces of the superlattice layer can effectively bend, block, or annihilate penetrating dislocations extending from the lower layer, preventing them from entering the multi-quantum well layer, thereby significantly reducing the non-radiative recombination center density of the multi-quantum well layer. Based on the above, the overall crystal quality of the epitaxial structure is improved, the stress environment is optimized, and the radiative recombination efficiency of the multi-quantum-well active region is significantly enhanced. In particular, for long-wavelength LEDs, the internal quantum efficiency and optical output power can be substantially improved. Furthermore, the LED epitaxial structure of this embodiment can be fully realized using conventional group III nitride growth processes such as MOCVD, without the need for complex patterned substrates or bonding techniques, making it easy to industrialize and promote.

[0052] In some embodiments of this application, in the step of forming the basic unit, an InGaN layer is first grown in an NH3 atmosphere, annealed, and then the temperature is maintained. The growth material is stopped, and only an NH3 atmosphere is introduced for surface reconstruction. Then the temperature is raised to grow a GaN layer. The surface reconstruction process takes 5s to 100s.

[0053] By adding a step to stop growth and reconstruct the surface during the growth process, the crystal quality of the film can be effectively improved, thereby enhancing the overall performance of the device.

[0054] refer to Figure 7a The superlattice layer (stress-relieving layer) is grown continuously without surface reconstruction, and its surface exhibits a distinct V-pit distribution. (Reference) Figure 7bThe improved scheme provided in this embodiment adds a superlattice layer (stress relief layer) after the surface reconstruction step of stopping growth, resulting in a smooth surface without obvious V-pits.

[0055] Example 3 This embodiment also provides an LED chip, including the LED epitaxial structure provided in Embodiment 1 above.

[0056] The LED chip provided in this embodiment includes the LED epitaxial structure provided in this application. By setting a superlattice layer with gradually increasing In content between the multi-quantum well layer and the n-type GaN layer as a first stress buffer layer, the huge lattice mismatch caused by the large difference in In content between the multi-quantum well bottom layer and the n-type GaN layer is transformed into a layer-by-layer release of stress by the multi-layer superlattice layer with gradually varying In content. This changes the stress release from a single interface to a multi-interface gradual process, avoiding the concentration of stress release at a single interface and effectively suppressing dislocation propagation and crack formation. Furthermore, since the In content in the first stress buffer layer gradually increases, the growth process starts with the layer with lower In content. In particular, the lower In composition of the initial layer provides a better crystal template for the subsequent growth of higher In content, improving the surface morphology and facilitating more effective incorporation and more uniform distribution of In atoms in the subsequent high-In layer. At the same time, the multiple interfaces of the superlattice layer can effectively bend, block, or annihilate penetrating dislocations extending from the lower layer, preventing them from entering the multi-quantum well layer, thereby significantly reducing the non-radiative recombination center density of the multi-quantum well layer. Based on the above, the overall crystal quality of the epitaxial structure is improved, the stress environment is optimized, and the radiative recombination efficiency of the multi-quantum-well active region is significantly enhanced. In particular, for long-wavelength LEDs, the internal quantum efficiency and optical output power can be substantially improved. Furthermore, the LED epitaxial structure of this embodiment can be fully realized using conventional group III nitride growth processes such as MOCVD, without the need for complex patterned substrates or bonding techniques, making it easy to industrialize and promote.

[0057] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. An LED epitaxial structure, characterized in that, include: Semiconductor substrate; An n-type GaN layer close to the semiconductor substrate; p-type GaN layer away from the semiconductor substrate; A multi-quantum-well layer located between the n-type GaN layer and the p-type GaN layer; A first stress-relieving layer located between the multi-quantum-well layer and the n-type GaN layer; The first stress relief layer is a superlattice layer formed by stacking multiple repeatedly stacked first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; In the direction from the n-type GaN layer to the p-type GaN layer, the In content in the first basic unit gradually increases.

2. The LED epitaxial structure according to claim 1, characterized in that, The In content in different first basic units increases linearly along the direction from the n-type GaN layer to the p-type GaN layer.

3. The LED epitaxial structure according to claim 1, characterized in that, All the first basic units are divided into several groups. The In content in the first basic units of different groups gradually increases along the direction from the n-type GaN layer to the p-type GaN layer. The In content in the first basic units of the same group is the same.

4. The LED epitaxial structure according to claim 1, characterized in that, Also includes: A second stress-relieving layer located between the multi-quantum-well layer and the p-type GaN layer; The second stress relief layer is a superlattice layer formed by stacking multiple repeating second basic units; each second basic unit includes an InGaN layer and a GaN layer on the InGaN layer; In the direction from the n-type GaN layer to the p-type GaN layer, the In content in the second basic unit gradually decreases.

5. The LED epitaxial structure according to claim 4, characterized in that, The In content in different second basic units decreases linearly along the direction from the n-type GaN layer to the p-type GaN layer.

6. The LED epitaxial structure according to claim 4, characterized in that, All the first basic units are divided into several groups. The In content in the first basic units of different groups gradually increases along the direction from the n-type GaN layer to the p-type GaN layer. The In content in the first basic units of the same group is the same. The In content in different second basic units decreases linearly along the direction from the n-type GaN layer to the p-type GaN layer.

7. The LED epitaxial structure according to claim 4, characterized in that, Also includes: Nucleation layer, located on the surface of the semiconductor substrate; The nucleation layer is a GaN layer; A buffer layer, which is an undoped GaN layer or an AlGaN layer, is located on the surface of the nucleation layer; the n-type GaN layer is located on the surface of the buffer layer. The semiconductor substrate is a sapphire substrate, a Si substrate, or a SiC substrate; The n-type GaN layer is a Si-doped GaN layer; The Si doping concentration is 1×10⁻⁶. 18 cm -3 ~5×10 19 cm -3 ; The multi-quantum-well layer is composed of multiple repetitive periodic quantum-well layers and quantum-barrier layers stacked alternately; the quantum-well layer is an InGaN layer, and the quantum-barrier layer is a GaN layer or an InGaN layer. The p-type GaN layer is a Mg-doped GaN layer; The Mg doping concentration is 5×10⁻⁶. 18 cm -3 ~5×10 20 cm -3 ; The LED epitaxial structure also includes: An electron blocking layer is located between the multiple quantum well layer and the p-type GaN layer; the electron blocking layer is a Mg-doped AlGaN layer. An ohmic contact layer is located on the surface of the p-type GaN layer away from the multi-quantum-well layer.

8. The LED epitaxial structure according to claim 7, characterized in that, In the first stress relief layer, along the direction from the n-type GaN layer to the p-type GaN layer, the In content gradually increases from 30% of the In content on the side of the multi-quantum well layer closer to the n-type GaN layer to 70% of the In content on the side of the multi-quantum well layer closer to the n-type GaN layer; the number of the first basic units is 3 to 15. In the second stress-relieving layer, along the direction from the n-type GaN layer to the p-type GaN layer, the In content gradually decreases from 70% of the In content on the side of the multi-quantum well layer near the p-type GaN layer to 30% of the In content on the side of the multi-quantum well layer near the p-type GaN layer; the number of the second basic units is 3 to 15. In the multiple quantum well layers, the thickness of the quantum well layer is 2nm~4nm, and the thickness of the quantum barrier layer is 5nm~20nm; the In content in the quantum well layer is 10%~25%; and the number of repetition periods of the quantum well layer and the quantum barrier layer is 10~30. The thickness of the nucleation layer is 2nm~5nm; The thickness of the buffer layer is 2μm~5μm; The thickness of the n-type GaN layer is 1μm~4μm; The thickness of the p-type GaN layer is 5nm~30nm; The thickness of the InGaN layer in the superlattice layer of the first stress relief layer is 10nm~30nm, and the thickness of the GaN layer is 5nm~15nm; the In content of the InGaN layer in the first stress relief layer is 2%~12%. The thickness of the InGaN layer in the superlattice layer of the second stress relief layer is 10 nm to 30 nm, and the thickness of the GaN layer is 5 nm to 15 nm; the In content of the InGaN layer in the second stress relief layer is 2% to 12%. The thickness of the electron blocking layer is 5nm~30nm.

9. A method for forming an LED epitaxial structure, characterized in that, Includes the following steps: Provide semiconductor substrates; An n-type GaN layer is formed close to the semiconductor substrate; A multi-quantum-well layer is formed on the side of the n-type GaN layer away from the semiconductor substrate; A p-type GaN layer is formed on the side of the multi-quantum-well layer away from the semiconductor substrate; Prior to forming the multi-quantum-well layer, the process also includes: A first stress relief layer is formed on the side of the n-type GaN layer away from the semiconductor substrate; the multiple quantum well layer is formed on the side of the first stress relief layer away from the semiconductor substrate; The first stress relief layer is a superlattice layer formed by stacking multiple repeatedly stacked first basic units; each first basic unit includes an InGaN layer and a GaN layer on the InGaN layer; In the direction from the n-type GaN layer to the p-type GaN layer, the In content in the first basic unit gradually increases.

10. The method for forming an LED epitaxial structure according to claim 9, characterized in that, In the step of forming the basic unit, First, an InGaN layer is grown in an NH3 atmosphere and annealed. Then, the temperature is maintained, the growth material is stopped, and only the NH3 atmosphere is introduced for surface reconstruction. After that, the temperature is increased to grow a GaN layer. The surface reconstruction process takes 5s to 100s.

11. An LED chip, characterized in that, Includes the LED epitaxial structure as described in any one of claims 1-8.

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