An LED epitaxial wafer for improving response speed of a device, a preparation method thereof, and an LED chip

Abstract

The application discloses an LED epitaxial wafer for improving device response speed, a preparation method thereof and an LED chip, and relates to the technical field of semiconductor devices.The epitaxial wafer comprises a substrate, and a buffer layer, a three-dimensional growth GaN layer, an undoped GaN layer, an n-type doped GaN layer, a stress release layer, a multi-quantum well layer, an electron blocking layer and a p-type doped GaN layer which are sequentially stacked on the substrate; wherein the stress release layer is a periodic superlattice structure, each period comprises an AlN layer, a compositionally graded AlGaN layer and a GaN layer which are sequentially stacked, and the Al composition in the compositionally graded AlGaN layer gradually changes from 100% near the AlN layer side to 0% near the GaN layer side along the epitaxial growth direction. The AlN / compositionally graded AlGaN / GaN superlattice structure is used as the stress release layer, so that the V-pit density can be greatly reduced, the active region defects and electron overflow can be reduced, the non-radiative recombination can be inhibited, the modulation bandwidth and the light-emitting efficiency of the Micro-LED can be simultaneously improved under high current density, and the application requirement of high-speed optical communication can be adapted.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, specifically to an LED epitaxial wafer and its preparation method for improving device response speed, and an LED chip. Background Technology

[0002] With the rapid development of 5G and 6G communication technologies and big data centers, traditional electrical signal transmission faces problems such as bandwidth bottlenecks and electromagnetic interference. Visible light communication and short-range optical communication technologies based on Micro-LEDs have become important development directions for next-generation communication technologies due to their advantages such as high bandwidth, low power consumption, and anti-interference. GaN-based Micro-LEDs, with their wide bandgap, high luminous efficiency, and fast response speed, are one of the core devices in the field of optical communication.

[0003] However, existing GaN-based Micro-LEDs still have key technical shortcomings in optical communication applications: First, the epitaxial layer structure design is unreasonable, resulting in a long recombination lifetime of charge carriers in the quantum well, making it difficult for the device bandwidth to exceed 3GHz and meet the high-speed transmission requirements of 10Gbps and above; Second, the hole injection efficiency of the electron blocking layer is low, and the charge carrier leakage problem is serious, which not only reduces the luminous efficiency but also further limits the bandwidth improvement; Third, the traditional MOCVD growth process makes it difficult to precisely control the energy level structure of the quantum well, resulting in uneven charge carrier distribution and affecting the high-frequency response characteristics of the device.

[0004] Currently, industry research on improving the bandwidth of GaN-based Micro-LEDs mainly focuses on optimizing device fabrication processes, such as reducing device size and optimizing electrode structures. However, there is relatively little research on the systematic optimization of epitaxial layer structures. Therefore, developing a structural design and fabrication method that can simultaneously improve the epitaxial bandwidth and luminous efficiency of GaN-based Micro-LEDs has become crucial for promoting the practical application of Micro-LED optical communication technology. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide an LED epitaxial wafer with improved device response speed, a method for its preparation, and an LED chip, in order to solve the above-mentioned technical problems described in the prior art.

[0006] A first aspect of the present invention is to provide an LED epitaxial wafer for improving device response speed, the epitaxial wafer comprising a substrate, and a buffer layer, a three-dimensionally grown GaN layer, an undoped GaN layer, an n-type doped GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer and a p-type doped GaN layer sequentially stacked on the substrate. The stress relief layer is a periodic superlattice structure, and each period includes an AlN layer, a composition-gradient AlGaN layer and a GaN layer stacked sequentially. In the composition-gradient AlGaN layer, the Al composition gradually changes from 100% near the AlN layer to 0% near the GaN layer along the epitaxial growth direction.

[0007] According to one aspect of the above technical solution, the stress relief layer has 3-6 cycles.

[0008] According to one aspect of the above technical solution, within a single cycle, the thickness of the AlN layer is 1nm-2nm, the thickness of the composition-gradient AlGaN layer is 1nm-2nm, and the thickness of the GaN layer is 1nm-2nm.

[0009] According to one aspect of the above technical solution, the buffer layer is a GaN buffer layer with a thickness of 15nm-35nm; the thickness of the three-dimensionally grown GaN layer is 500nm-2000nm; the thickness of the undoped GaN layer is 800nm-1200nm; and the thickness of the n-type doped GaN layer is 1000nm-3000nm.

[0010] According to one aspect of the above technical solution, the multiple quantum well layer is a periodic structure in which InGaN well layers and GaN barrier layers are grown alternately, with a period number of 8-16; wherein the thickness of the InGaN well layer is 2nm-4nm, and the thickness of the GaN barrier layer is 10nm-15nm.

[0011] According to one aspect of the above technical solution, the electron blocking layer is a periodic structure in which AlGaN layers and GaN layers are grown alternately, with a total thickness of 10nm-100nm; the thickness of the p-type doped GaN layer is 5nm-100nm.

[0012] A second aspect of the present invention is to provide a method for growing an epitaxial wafer to improve the response speed of a device, for preparing the LED epitaxial wafer described in the above-mentioned technical solution, the method comprising: Provide a substrate; A buffer layer, a three-dimensional GaN layer, an undoped GaN layer, and an n-type doped GaN layer are sequentially grown on the substrate. A stress relief layer is grown on the n-type doped GaN layer. The stress relief layer is a periodic superlattice structure. In each period, an AlN layer, a composition-gradient AlGaN layer, and a GaN layer are grown sequentially. When growing the composition-gradient AlGaN layer, the Al composition is gradually changed from 100% to 0 along the epitaxial growth direction by adjusting the MO source flow rate. A multi-quantum well layer, an electron blocking layer, and a p-type doped GaN layer are sequentially grown on the stress relief layer.

[0013] According to one aspect of the above technical solution, when growing the stress-relieving AlN layer, the composition-gradient AlGaN layer and the GaN layer, the growth temperature is 800℃-900℃, the growth pressure is 100 torr-300 torr, and the growth atmosphere is a mixed atmosphere of N2, H2 and NH3, wherein N2 and H2 are used as carrier gases and NH3 is used as a reaction gas.

[0014] According to one aspect of the above technical solution, the AlN layer is grown using trimethylaluminum as the MO source; the composition-gradient AlGaN layer is grown using trimethylaluminum and trimethylgallium as the MO source; and the GaN layer is grown using trimethylgallium as the MO source.

[0015] A third aspect of the present invention is to provide a Micro-LED chip, including the LED epitaxial wafer described in the above technical solutions for improving device response speed.

[0016] Compared with existing technologies, the advantages of using the LED epitaxial wafer and its growth method to improve device response speed, and the Micro-LED chip shown in this invention are as follows: This invention sets the stress relief layer as a superlattice periodic structure of AlN / composed graded AlGaN / GaN, and uses the Al compositional graded transition to alleviate lattice mismatch, which can significantly reduce V-pit density, reduce active region defects, achieve interface flattening and steepening, reduce electron overflow and non-radiative recombination centers, and simultaneously improve the modulation bandwidth and luminous efficiency of the device under high current density operating conditions, thus meeting the high-speed transmission requirements of Micro-LED optical communication. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the structure of an LED epitaxial wafer for improving device response speed in one embodiment of the present invention; Figure 2 This is a schematic diagram of the stress relief layer in one embodiment of the present invention; Figure 3 This is a schematic flowchart of an LED epitaxial wafer fabrication method for improving device response speed in one embodiment of the present invention; Explanation of symbols in the attached drawings: Substrate 1, Buffer layer 2, 3D grown GaN layer 3, Undoped GaN layer 4, n-type doped GaN layer 5, Stress relief layer 6, Multiple quantum well layer 7, Electron blocking layer 8, p-type doped GaN layer 9. Detailed Implementation

[0018] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be more thorough and complete.

[0019] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] First, it should be noted that the stress relief layer of conventional GaN-based Micro-LED epitaxial wafers often adopts a periodic structure with alternating growth of InGaN and GaN. This structure can improve luminous efficiency through V-pits under low current density in the lighting field. However, under the high current density of thousands of A / cm² in optical communication applications, the positive effect of V-pits is greatly weakened. Instead, it will form leakage channels, aggravate electron overflow, and introduce a large number of non-radiative recombination centers, ultimately leading to a decrease in device luminous efficiency and limited modulation bandwidth. Typically, the device bandwidth can only reach tens to hundreds of MHz, which is difficult to meet the application requirements of high-speed optical communication.

[0022] A first aspect of the present invention is to provide an LED epitaxial wafer for improving device response speed, the epitaxial wafer comprising a substrate, and a buffer layer, a three-dimensionally grown GaN layer, an undoped GaN layer, an n-type doped GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer, and a p-type doped GaN layer sequentially stacked on the substrate; wherein the stress relief layer is a periodic superlattice structure, each period comprising an AlN layer, a composition-gradient AlGaN layer, and a GaN layer sequentially stacked, wherein the Al composition in the composition-gradient AlGaN layer gradually changes from 100% near the AlN layer to 0% near the GaN layer along the epitaxial growth direction.

[0023] Furthermore, the stress relief layer has 3-6 cycles.

[0024] Furthermore, within a single cycle, the thickness of the AlN layer is 1nm-2nm, the thickness of the composition-gradient AlGaN layer is 1nm-2nm, and the thickness of the GaN layer is 1nm-2nm.

[0025] Furthermore, the buffer layer is a GaN buffer layer with a thickness of 15nm-35nm; the thickness of the three-dimensionally grown GaN layer is 500nm-2000nm; the thickness of the undoped GaN layer is 800nm-1200nm; and the thickness of the n-type doped GaN layer is 1000nm-3000nm.

[0026] Furthermore, the multiple quantum well layer is a periodic structure in which InGaN well layers and GaN barrier layers are grown alternately, with a period number of 8-16; wherein the thickness of the InGaN well layer is 2nm-4nm, and the thickness of the GaN barrier layer is 10nm-15nm.

[0027] Furthermore, the electron blocking layer is a periodic structure with alternating AlGaN and GaN layers, and the total thickness is 10nm-100nm; the thickness of the p-type doped GaN layer is 5nm-100nm.

[0028] A second aspect of the present invention provides an epitaxial wafer growth method for improving device response speed, used to prepare the aforementioned LED epitaxial wafer. The method includes: providing a substrate; sequentially growing a buffer layer, a three-dimensionally grown GaN layer, an undoped GaN layer, and an n-type doped GaN layer on the substrate; growing a stress relief layer on the n-type doped GaN layer, the stress relief layer being a periodic superlattice structure, wherein an AlN layer, a composition-gradient AlGaN layer, and a GaN layer are sequentially grown in each period, wherein during the growth of the composition-gradient AlGaN layer, the Al composition is gradually changed from 100% to 0 along the epitaxial growth direction by adjusting the MO source flow rate; and sequentially growing a multi-quantum well layer, an electron blocking layer, and a p-type doped GaN layer on the stress relief layer.

[0029] Furthermore, when growing the stress-relieving AlN layer, the composition-gradient AlGaN layer, and the GaN layer, the growth temperature is 800℃-900℃, the growth pressure is 100 torr-300 torr, and the growth atmosphere is a mixture of N2, H2, and NH3, wherein N2 and H2 are used as carrier gases and NH3 is used as a reaction gas.

[0030] Furthermore, the AlN layer is grown using trimethylaluminum as the MO source; the composition-gradient AlGaN layer is grown using trimethylaluminum and trimethylgallium as MO sources; and the GaN layer is grown using trimethylgallium as the MO source.

[0031] A third aspect of the present invention is to provide a Micro-LED chip comprising the aforementioned LED epitaxial wafer for improving device response speed.

[0032] Compared with existing technologies, the advantages of using the LED epitaxial wafer and its growth method to improve device response speed, and the Micro-LED chip shown in this invention are as follows: This invention sets the stress relief layer as a superlattice periodic structure of AlN / composed graded AlGaN / GaN, and uses the Al compositional graded transition to alleviate lattice mismatch, which can significantly reduce V-pit density, reduce active region defects, achieve interface flattening and steepening, reduce electron overflow and non-radiative recombination centers, and simultaneously improve the modulation bandwidth and luminous efficiency of the device under high current density operating conditions, thus meeting the high-speed transmission requirements of Micro-LED optical communication.

[0033] Example 1 Please see Figure 1 and Figure 2 The first embodiment of the present invention provides an LED epitaxial wafer for improving device response speed. The epitaxial wafer shown in this embodiment includes: Substrate 1, and a buffer layer 2, a three-dimensionally grown GaN layer 3, an undoped GaN layer 4, an n-type doped GaN layer 5, a stress relief layer 6, a multiple quantum well layer 7, an electron blocking layer 8, and a p-type doped GaN layer 9 sequentially stacked on the substrate 1.

[0034] In this embodiment, substrate 1 is preferably a sapphire substrate, i.e., an Al2O3 substrate. In this embodiment, buffer layer 2 is a GaN buffer layer with a growth thickness of 25 nm, used to alleviate the lattice mismatch between the substrate and the subsequent GaN epitaxial layer and improve the quality of the epitaxial crystal.

[0035] In this embodiment, the thickness of the three-dimensional GaN layer 3 is 1200 nm. Trimethylgallium (TMGa) is used as the MO source, the growth temperature is 1100 °C, and the growth atmosphere is a mixture of N2, H2 and NH3, wherein N2 and H2 are used as carrier gases, NH3 is used as a reactant gas, and the growth pressure is 200 torr. This layer releases stress through the three-dimensional growth mode, thereby reducing the dislocation density of the epitaxial layer.

[0036] In this embodiment, the undoped GaN layer 4 has a growth thickness of 1000 nm and uses trimethylgallium as the MO source to further improve crystal quality and provide a smooth growth interface for subsequent doped layers. In this embodiment, the n-type doped GaN layer 5 has a growth thickness of 2000 nm, uses trimethylgallium as the MO source, and is doped with Si to serve as an n-type semiconductor layer to provide electrons for the device.

[0037] In this embodiment, the stress relief layer 6 is a periodic superlattice structure. Each period includes sequentially stacked AlN layer 6-1, composition-gradient AlGaN layer 6-2, and GaN layer 6-3. In this embodiment, the stress relief layer has four periods. Within a single period, the thickness of AlN layer 6-1 is 1.5 nm, the thickness of composition-gradient AlGaN layer 6-2 is 1.5 nm, and the thickness of GaN layer 6-3 is 1.5 nm.

[0038] Specifically, in the composition-gradient AlGaN layer 6-2, the Al composition gradually changes from 100% near the AlN layer to 0% near the GaN layer along the epitaxial growth direction. Through the continuous gradual transition of the Al composition, the lattice mismatch between AlN and GaN is alleviated, interface defects are reduced, and the large-scale generation of V-pits is suppressed. This reduces the risk of leakage and electron overflow under high current density, reduces non-radiative recombination centers, and improves the carrier recombination rate and device response speed.

[0039] In this embodiment, the multiple quantum well layer 7 is a periodic structure with alternating growth of InGaN well layers and GaN barrier layers, with a period number of 12; wherein the thickness of the InGaN well layer is 3nm and the thickness of the GaN barrier layer is 12nm, serving as an active region to realize radiative recombination luminescence of electrons and holes.

[0040] In this embodiment, the electron blocking layer 8 is a periodic structure with alternating AlGaN and GaN layers, with a total thickness of 50 nm, used to block electrons from overflowing into the p-type layer and improve carrier confinement efficiency.

[0041] In this embodiment, the p-type doped GaN layer 9 has a thickness of 50 nm and is doped with Mg, serving as a p-type semiconductor layer to provide holes for the device.

[0042] Please see Figure 3 In this embodiment, the growth method for fabricating the LED epitaxial wafer with improved device response speed includes steps S10-S40: Step S10: Provide a substrate.

[0043] In this embodiment, a sapphire substrate, namely an Al2O3 substrate, is used as the substrate. The substrate is placed in the MOCVD reaction chamber for high-temperature pretreatment to remove surface impurities.

[0044] Step S20: A buffer layer, a three-dimensional GaN layer, an undoped GaN layer, and an n-type doped GaN layer are sequentially grown on the substrate.

[0045] Specifically, the growth temperature was set to 550℃, the growth pressure to 200 torr, and a GaN buffer layer with a thickness of 25nm was grown on the substrate. The growth temperature was increased to 1100℃ and the growth pressure was adjusted to 200 torr. A three-dimensional GaN layer with a thickness of 1200 nm was grown on the buffer layer. While keeping the growth temperature and pressure constant, an undoped GaN layer with a thickness of 1000 nm was grown on the three-dimensional GaN layer. While keeping the growth temperature and pressure constant, silane was introduced as the Si doping source to grow an n-type doped GaN layer on the undoped GaN layer with a thickness of 2000 nm.

[0046] Step S30: A stress relief layer is grown on the n-type doped GaN layer.

[0047] The stress relief layer is a periodic superlattice structure, in which an AlN layer, a compositionally graded AlGaN layer, and a GaN layer are grown sequentially in each cycle, and the growth is repeated for 4 cycles.

[0048] Specifically, a single cycle of growing the stress-relieving layer includes steps S31-S33: Step S31: Set the growth temperature to 850℃, the growth pressure to 200 torr, and the growth atmosphere to a mixed atmosphere of N2, H2 and NH3. Use trimethylaluminum as the MO source to grow an AlN layer with a growth thickness of 1.5 nm. Step S32: Keep the growth temperature, pressure and atmosphere constant, and simultaneously introduce trimethylaluminum and trimethylgallium to grow a compositionally gradient AlGaN layer with a thickness of 1.5 nm. During the growth process, gradually reduce the flow rate of trimethylaluminum and simultaneously increase the flow rate of trimethylgallium so that the Al composition of the AlGaN layer gradually changes from 100% near the AlN layer to 0 near the GaN layer. In step S33, while keeping the growth temperature, pressure and atmosphere constant, a GaN layer with a thickness of 1.5 nm is grown using trimethylgallium as the MO source, completing a single cycle of stress relief layer growth.

[0049] Step S40: A multi-quantum well layer, an electron blocking layer, and a p-type doped GaN layer are sequentially grown on the stress relief layer.

[0050] Specifically, the growth temperature was adjusted to 780℃ and the growth pressure was adjusted to 200 torr. InGaN well layers and GaN barrier layers were alternately grown on the stress relief layer and repeated for 12 cycles to obtain a multi-quantum well layer. The growth temperature was increased to 1050℃ and the growth pressure was adjusted to 80 torr. AlGaN layers and GaN layers were alternately grown on the multi-quantum well layer to obtain an electron blocking layer with a total thickness of 50nm. The growth temperature was adjusted to 1000℃, the growth pressure was adjusted to 300 torr, and magnesia-dicerocene was introduced as the Mg doping source to grow a p-type doped GaN layer on the electron blocking layer with a growth thickness of 50 nm. After growth is complete, the temperature is lowered to 750℃ and the epitaxial wafer is annealed in a N2 atmosphere for 10 minutes. The epitaxial growth ends when the temperature is lowered to room temperature.

[0051] It should be noted that during the growth of the epitaxial wafer, trimethylaluminum (TMAl), trimethylindium (TMIn), and trimethylgallium (TMGa) are used as precursors for group III sources, ammonia (NH3) is used as a precursor for group V sources, silane (SiH4) and magnesium pyrocene (Cp2Mg) are used as precursors for N-type and P-type dopants, respectively, and N2 and H2 are used as carrier gases.

[0052] Using the growth method shown in this embodiment, an LED epitaxial wafer with improved device response speed can be prepared. By using this epitaxial wafer to fabricate a chip, a Micro-LED chip can be obtained.

[0053] Specifically, the Micro-LED chip has a chip size of 15μm×30μm and a test current of 30mA. After performance testing, the chip showed significant improvements in modulation bandwidth and luminous efficiency, and all other indicators were good.

[0054] Example 2 The second embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the AlN layer in a single cycle of the stress relief layer is 0.5 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0055] Example 3 The third embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the AlN layer in a single cycle of the stress relief layer is 1 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0056] Example 4 The fourth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the AlN layer in a single cycle of the stress relief layer is 2 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0057] Example 5 The fifth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the AlN layer in a single cycle of the stress relief layer is 3 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0058] Example 6 The sixth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the composition-gradient AlGaN layer in a single cycle of the stress relief layer is 0.5 nm, while the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0059] Example 7 The seventh embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the composition-gradient AlGaN layer in a single cycle of the stress relief layer is 1 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0060] Example 8 The eighth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the composition-gradient AlGaN layer in a single cycle of the stress relief layer is 2 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0061] Example 9 The ninth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the thickness of the composition-gradient AlGaN layer in a single cycle of the stress relief layer is 3 nm, and the thickness, number of cycles, and growth parameters of the other layers are consistent with those in Embodiment 1.

[0062] Example 10 The tenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the GaN layer thickness in a single cycle of the stress relief layer is 0.5 nm, while the thickness of the remaining layers, the number of cycles, and the growth parameters are consistent with those in Embodiment 1.

[0063] Example 11 The eleventh embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the GaN layer thickness in a single cycle of the stress relief layer is 1 nm, while the thickness of the remaining layers, the number of cycles, and the growth parameters are consistent with those in Embodiment 1.

[0064] Example 12 The twelfth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the GaN layer thickness in a single cycle of the stress relief layer is 2 nm, while the thickness of the remaining layers, the number of cycles, and the growth parameters are consistent with those in Embodiment 1.

[0065] Example 13 The thirteenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the GaN layer thickness in a single cycle of the stress relief layer is 3 nm, while the thickness of the remaining layers, the number of cycles, and the growth parameters are consistent with those in Embodiment 1.

[0066] Example 14 The fourteenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the stress relief layer has two cycles, and the thickness and growth parameters of the other layers are consistent with those in Embodiment 1.

[0067] Example 15 The fifteenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the stress relief layer has 3 cycles, and the thickness and growth parameters of the other layers are consistent with those in Embodiment 1.

[0068] Example 16 The sixteenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the stress relief layer has 5 cycles, and the thickness and growth parameters of the other layers are consistent with those in Embodiment 1.

[0069] Example 17 The seventeenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the stress relief layer has 6 cycles, and the thickness and growth parameters of the other layers are consistent with those in Embodiment 1.

[0070] Example 18 The eighteenth embodiment of the present invention also provides an LED epitaxial wafer for improving device response speed, which is basically similar to the first embodiment, except that: In this embodiment, the stress relief layer has 7 cycles, and the thickness and growth parameters of the other layers are consistent with those in Embodiment 1.

[0071] Comparative Example 1 The first comparative example of the present invention also provides an LED epitaxial wafer, which is basically similar to the first embodiment, except that: In this comparative example, the stress relief layer adopts a periodic structure with alternating growth of conventional InGaN and GaN layers, instead of a superlattice structure of AlN / composition-gradient AlGaN / GaN.

[0072] Table 1 is a comparison table of parameters and performance between Examples 1 to 18 of the present invention and Comparative Example 1: Table 1

[0073] As shown in Table 1, by setting the stress relief layer as a periodic superlattice structure of AlN / composition-gradient AlGaN / GaN, the present invention can effectively improve the modulation bandwidth of Micro-LED devices and improve luminous efficiency.

[0074] As shown in the first embodiment, its modulation bandwidth reaches 1.98GHz, which is more than 500% higher than the 325MHz of the conventional structure shown in Comparative Example 1; the luminous brightness reaches 5.48mW, which is 5.17% higher than 100% of Comparative Example 1, reaching 105.17%, while the operating voltage remains basically the same. This shows that the present invention achieves a dual improvement in bandwidth and luminous efficiency without deteriorating the electrical performance of the device.

[0075] Comparison of examples with different thicknesses and number of cycles shows that when the thickness of the AlN layer, the composition-gradient AlGaN layer, and the GaN layer are all 1.5 nm and the number of cycles is 4, the overall performance of the device is optimal. When the thickness of a single layer is too thin or too thick, or the number of cycles is too few or too many, the bandwidth and luminous efficiency will decrease to varying degrees, indicating that the parameter range defined in this invention can achieve the best balance between stress release and defect suppression.

[0076] In summary, the key feature of this invention is that by employing a stress-relieving layer with an AlN / composition-gradient AlGaN / GaN superlattice structure, the lattice mismatch is alleviated by the Al composition gradient, the V-pits density is significantly reduced, and the non-radiative recombination centers and electron overflow in the active region are reduced, thereby significantly improving the response speed and modulation bandwidth of Micro-LED devices while maintaining luminous efficiency. This invention is suitable for the fabrication of Micro-LED devices in the field of high-speed optical communication.

[0077] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0078] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An LED epitaxial wafer for improving device response speed, characterized in that, The epitaxial wafer includes a substrate, and a buffer layer, a three-dimensionally grown GaN layer, an undoped GaN layer, an n-type doped GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer and a p-type doped GaN layer, which are sequentially stacked on the substrate. The stress relief layer is a periodic superlattice structure, and each period includes an AlN layer, a composition-gradient AlGaN layer and a GaN layer stacked sequentially. In the composition-gradient AlGaN layer, the Al composition gradually changes from 100% near the AlN layer to 0% near the GaN layer along the epitaxial growth direction.

2. The LED epitaxial wafer according to claim 1, characterized in that, The stress relief layer has 3-6 cycles.

3. The LED epitaxial wafer according to claim 2, characterized in that, Within a single cycle, the thickness of the AlN layer is 1nm-2nm, the thickness of the composition-gradient AlGaN layer is 1nm-2nm, and the thickness of the GaN layer is 1nm-2nm.

4. The LED epitaxial wafer according to claim 1, characterized in that, The buffer layer is a GaN buffer layer with a thickness of 15nm-35nm; the thickness of the three-dimensionally grown GaN layer is 500nm-2000nm; the thickness of the undoped GaN layer is 800nm-1200nm; and the thickness of the n-type doped GaN layer is 1000nm-3000nm.

5. The LED epitaxial wafer according to claim 1, characterized in that, The multiple quantum well layer is a periodic structure in which InGaN well layers and GaN barrier layers are grown alternately, with a period number of 8-16; wherein the thickness of the InGaN well layer is 2nm-4nm, and the thickness of the GaN barrier layer is 10nm-15nm.

6. The LED epitaxial wafer according to claim 1, characterized in that, The electron blocking layer is a periodic structure with alternating AlGaN and GaN layers, and the total thickness is 10nm-100nm; the thickness of the p-type doped GaN layer is 5nm-100nm.

7. An epitaxial wafer growth method for improving device response speed, characterized in that, The method for preparing the LED epitaxial wafer according to any one of claims 1-6 comprises: Provide a substrate; A buffer layer, a three-dimensional GaN layer, an undoped GaN layer, and an n-type doped GaN layer are sequentially grown on the substrate. A stress relief layer is grown on the n-type doped GaN layer. The stress relief layer is a periodic superlattice structure. In each period, an AlN layer, a composition-gradient AlGaN layer, and a GaN layer are grown sequentially. When growing the composition-gradient AlGaN layer, the Al composition is gradually changed from 100% to 0 along the epitaxial growth direction by adjusting the MO source flow rate. A multi-quantum well layer, an electron blocking layer, and a p-type doped GaN layer are sequentially grown on the stress relief layer.

8. The epitaxial wafer growth method according to claim 7, characterized in that, When growing the stress-relieving AlN layer, the composition-gradient AlGaN layer, and the GaN layer, the growth temperature is 800℃-900℃, the growth pressure is 100 torr-300 torr, and the growth atmosphere is a mixture of N2, H2, and NH3, wherein N2 and H2 are used as carrier gases and NH3 is used as a reactant gas.

9. The epitaxial wafer growth method according to claim 8, characterized in that, The AlN layer is grown using trimethylaluminum as the MO source; the composition-gradient AlGaN layer is grown using trimethylaluminum and trimethylgallium as MO sources; and the GaN layer is grown using trimethylgallium as the MO source.

10. A Micro-LED chip, characterized in that, The LED epitaxial wafer comprising any one of claims 1-6 for improving device response speed.

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