LED epitaxial wafer preparation method and micro-led

Abstract

The application provides an LED epitaxial wafer preparation method and a Micro-LED. A three-dimensional growth layer is grown by adopting a composite segmented growth, Al atoms with small characteristics are used to fill vacancies in the growth of GaN, vacancies in the growth of AlGaN are further filled by Al processing, then recrystallization baking is performed to remove GaN with poor combination and make it decompose to reserve the tightly combined part. Then the temperature is gradually increased by circulation, and the three-dimensional growth is gradually changed into two-dimensional growth, so that the defects are annihilated when changing into two-dimensional, thereby greatly reducing the defect density. Due to the great reduction of the defect density, non-radiative recombination can be inhibited, and the carrier recombination rate can be accelerated, thereby optimizing the electrical-optical response speed of the device. Meanwhile, the quantum confinement Stark effect (QCSE) can be inhibited, the wave function overlap can be increased, the radiative recombination rate can be improved, and the modulation bandwidth can be directly improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for preparing LED epitaxial wafers and Micro-LEDs. 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] Existing GaN-based Micro-LEDs still have key technological 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.

[0005] GaN-based Micro-LEDs grown on traditional sapphire substrates have two major problems: First, the lattice mismatch rate between sapphire and GaN is as high as 16%, which leads to the introduction of high-density dislocations in the epitaxial layer. This not only reduces luminous efficiency but also increases leakage current and deteriorates the device's response speed. Second, since sapphire is an insulating substrate, the current needs to diffuse laterally in the GaN epitaxial layer. However, the traditional epitaxial structure has a large N-type GaN layer thickness and a high P-type GaN layer resistance, resulting in an excessively large RC (resistance-capacitance) time constant of the device, which is difficult to meet the high modulation bandwidth requirements of optical communication scenarios.

[0006] At present, the mainstream methods for reducing the dislocation density of GaN epitaxy include growing an AlN buffer layer, using a patterned substrate, etc. However, there is still a lattice mismatch between AlN and GaN, and the patterned substrate process is complex, which will increase the parasitic capacitance of the device. For the optimization of the RC time, it mainly focuses on the electrode design in the chip preparation stage, such as reducing the electrode spacing, using a transparent conductive layer, etc., but the intrinsic resistance and structural capacitance problems of the material are not solved from the source of epitaxial growth. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide a method for preparing an LED epitaxial wafer and a Micro-LED, aiming to significantly reduce the defect density and improve the modulation bandwidth of the prepared Micro-LED.

[0008] According to an LED epitaxial wafer preparation method in an embodiment of the present invention, the method includes: Using a composite segmented growth method to prepare a three-dimensional growth layer, specifically including: Step 1, grow a GaN layer, using N2 and H2 as carrier gases, and simultaneously introduce NH3 and TMGa; Step 2, grow an Al x Ga (1-x) N layer, 0 < x < 1, and at this time, introduce TMAl on the basis of Step 1; Step 3, perform Al treatment. At this time, only retain N2 as the carrier gas, close H2 and NH3, and only introduce TMAl; Step 4, perform recrystallization treatment, introduce N2 and NH3, stop introducing TMAl, and prepare a three-dimensional growth sub-layer; Repeat Steps 1 to 4 to prepare the three-dimensional growth layer formed by stacking several three-dimensional growth sub-layers. Among them, the growth temperature in the current cycle process is higher than that in the previous cycle process.

[0009] Further, the method further includes: Provide a substrate; Deposit a buffer layer, the three-dimensional growth 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 on the substrate in sequence.

[0010] Further, the thickness of the three-dimensional growth layer is 400 nm to 1200 nm.

[0011] Further, the growth temperature in the first cycle process is 900 °C to 1000 °C, and the growth pressure is 100 torr to 600 torr.

[0012] Furthermore, the growth temperature in the current cycle is 20°C to 50°C higher than the growth temperature in the previous cycle, and the number of cycles is 2 to 6.

[0013] Furthermore, the thickness of the GaN layer in step one is 100nm~300nm.

[0014] Furthermore, in step two, Al x Ga (1-x) The thickness of the N layer is 100nm~300nm.

[0015] Furthermore, the processing time for the AI ​​process in step three is 10 to 30 seconds.

[0016] Furthermore, the recrystallization process in step four takes 10 to 60 seconds. According to an embodiment of the present invention, a Micro-LED is prepared according to the above-described LED epitaxial wafer preparation method.

[0017] This invention provides a method for fabricating LED epitaxial wafers and a Micro-LED. The method employs a composite segmented growth process to grow a three-dimensional growth layer. AlGaN is grown, utilizing the small size of Al atoms to fill vacancies during GaN growth. Al treatment further fills these vacancies. Recrystallization and baking remove loosely bonded GaN, decomposing it and retaining tightly bonded portions. By gradually increasing the cyclic temperature, the growth process transitions from three-dimensional to two-dimensional, causing defects to annihilate during the transition and significantly reducing defect density. This substantial reduction in defect density suppresses non-radiative recombination and accelerates carrier recombination rates, thereby optimizing the device's electro-optic response speed. It also suppresses the quantum confinement Stark effect (QCSE), increases wavefunction overlap, enhances the radiative recombination rate, and directly improves the modulation bandwidth. Detailed Implementation

[0018] This 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 this invention will be 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 description of the 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] The LED epitaxial wafer in this embodiment of the invention includes a substrate and a buffer layer, the three-dimensional growth 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 stacked sequentially on the substrate.

[0022] Among them, the substrate can be a planar sapphire substrate or a patterned sapphire substrate; the material of the buffer layer is GaN, and the thickness is 15 nm to 35 nm. Exemplarily, the thickness of the buffer layer is 15 nm, 20 nm, 25 nm, 30 nm, or 35 nm, etc., but not limited thereto; the thickness of the three-dimensional growth layer is 400 to 1200 nm. Exemplarily, the thickness of the three-dimensional growth layer is 400 nm, 600 nm, 800 nm, 1000 nm, or 1200 nm, etc., but not limited thereto; the thickness of the undoped GaN layer can be 800 nm to 1200 nm. Exemplarily, the thickness is 800 nm, 900 nm, 1000 nm, 1100 nm, or 1200 nm, etc., but not limited thereto, and TMGa is used as the MO source; the thickness of the n-type doped GaN layer is 1000 nm to 3000 nm. Exemplarily, the thickness is 1000 nm, 1500 nm, 2000 nm, 2500 nm, or 3000 nm, etc., but not limited thereto, and TMGa is used as the MO source, and this layer is used to provide electrons; the stress release layer can be a periodic structure formed by alternating growth of InGaN layers and GaN layers; the multi-quantum well layer can be a periodic structure formed by alternating growth of InGaN layers and GaN layers. Among them, the thickness of the InGaN layer can be 2 nm to 4 nm, the thickness of the GaN layer can be 10 nm to 15 nm, and the number of periods is 2 to 16. Exemplarily, the thickness of the InGaN layer is 2 nm, 3 nm, or 4 nm, etc., the thickness of the GaN layer is 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, or 15 nm, etc., and the number of periods is 2, 4, 6, 8, 10, 12, 14, or 16, etc., but not limited thereto; the electron blocking layer can be a periodic structure formed by alternating growth of AlGaN layers and GaN layers, and the thickness can be 10 nm to 100 nm. Exemplarily, the thickness is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, etc., but not limited thereto; the thickness of the p-type doped GaN layer is 5 nm to 100 nm, and this layer is used to provide holes. Exemplarily, the thickness is 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, etc., but not limited thereto.

[0023] It should be noted that the three-dimensional growth layer is a composite structure formed by stacking a number of three-dimensional growth sub-layers, and each three-dimensional growth sub-layer is obtained by sequentially stacking a GaN layer and an Al x Ga (1-x) N layer, where 0 < x < 1, and then through Al treatment and recrystallization treatment.

[0024] The embodiment of the present invention provides a method for preparing an LED epitaxial wafer. The method for preparing the LED epitaxial wafer specifically includes: Providing a substrate; A buffer layer, the three-dimensional growth 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 are sequentially deposited on the substrate; Among them, the three-dimensional growth layer is prepared by a composite segmented growth method, specifically including: Step 1, grow a GaN layer, using N2 and H2 as carrier gases, and simultaneously introduce NH3 and TMGa. The thickness of the GaN layer grown in this step is 100 nm to 300 nm; Step 2, grow an Al x Ga (1-x) N layer, 0 < x < 1. At this time, TMAI is introduced on the basis of Step 1. The thickness of the Al x Ga (1-x) N layer grown in this step is 100 nm to 300 nm; Step 3, perform Al treatment. At this time, only N2 is retained as the carrier gas, H2 and NH3 are turned off, and only TMAI is introduced. Al atoms are decomposed at high temperature, and the treatment time is 10 seconds to 30 seconds; Step 4, perform recrystallization treatment, introduce N2 and NH3, stop introducing TMAI, and prepare a three-dimensional growth sub-layer. The treatment time is 10 seconds to 60 seconds; Steps 1 to 4 are cycled to prepare the three-dimensional growth layer formed by stacking several three-dimensional growth sub-layers. Among them, the growth temperature in the current cycle process is higher than that in the previous cycle process.

[0025] Furthermore, the thickness of the three-dimensional growth layer is 400 nm to 1200 nm.

[0026] It should be noted that the growth temperature in the first cycle process is 900 °C to 1000 °C, the growth pressure is 100 torr to 600 torr. In addition, the growth temperature in the current cycle process is increased by 20 °C to 50 °C compared with that in the previous cycle process, and the number of cycles is 2 to 6 times. It can be understood that the second cycle is grown in the same way, only the temperature is increased by 20 °C to 50 °C on the basis of the first cycle. Similarly, the third, fourth, and even more cycles are grown in the same way, only the growth temperature is increased by 20 °C to 50 °C on the basis of the previous cycle, and the number of cycles can be 2 to 6 times.

[0027] The following further illustrates the present invention with specific examples: Example 1 The method for preparing an LED epitaxial wafer provided in Example 1 of the present invention specifically includes: Provide a substrate; A buffer layer, the three-dimensional growth 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 are sequentially deposited on the substrate; Among them, the three-dimensional growth layer is prepared by a composite segmented growth method, which specifically includes: Step 1: Grow a GaN layer. Using N2 and H2 as carrier gases, NH3 and TMGa are simultaneously introduced. The thickness of the GaN layer grown in this step is 100 nm; Step 2: Grow an Al x Ga (1-x) N layer, where 0 < x < 1. At this time, TMAl is introduced based on the situation in Step 1. The thickness of the Al x Ga (1-x) N layer grown in this step is 100 nm; Step 3: Perform Al treatment. At this time, only N2 is retained as the carrier gas, H2 and NH3 are turned off, and only TMAl is introduced. Al atoms are decomposed at high temperature, and the treatment time is 20 seconds; Step 4: Perform recrystallization treatment. N2 and NH3 are introduced, and TMAl is stopped being introduced to prepare a three-dimensional growth sublayer. The treatment time is 20 seconds; Steps 1 to 4 are cycled to prepare the three-dimensional growth layer composed of several stacked three-dimensional growth sublayers. Among them, the growth temperature in the current cycle process is higher than that in the previous cycle process.

[0028] Furthermore, the thickness of the three-dimensional growth layer is 400 nm to 1200 nm.

[0029] It should be noted that the growth temperature in the first cycle process is 900 °C, the growth pressure is 600 torr. In addition, the growth temperature in the current cycle process is 35 °C higher than that in the previous cycle process, and the number of cycles is 4 times. It can be understood that the second cycle is grown in the same way, only raising the temperature by 35 °C based on the first cycle. Similarly, the third and fourth cycles are also grown in the same way, only raising the growth temperature by 35 °C based on the previous cycle.

[0030] Example 2 Example 2 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Example 1 is that the number of cycles is 1 time.

[0031] Example 3 Example 3 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Example 1 is that the number of cycles is 2 times.

[0032] Example 4 Embodiment 4 of the present invention also provides a method for preparing an LED epitaxial wafer, the difference from Embodiment 1 being that the number of cycles is 3.

[0033] Example 5 Embodiment 5 of the present invention also provides a method for preparing an LED epitaxial wafer, the difference from Embodiment 1 being that the number of cycles is 5.

[0034] Example 6 Embodiment 6 of the present invention also provides a method for preparing an LED epitaxial wafer, the difference from Embodiment 1 being that the number of cycles is 6.

[0035] Example 7 Embodiment 7 of the present invention also provides a method for preparing an LED epitaxial wafer, the difference from Embodiment 1 being that the number of cycles is 7.

[0036] Example 8 Embodiment 8 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Embodiment 1 is that the growth temperature in the current cycle is 15°C higher than the growth temperature in the previous cycle.

[0037] Example 9 Embodiment 9 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Embodiment 1 is that the growth temperature in the current cycle is increased by 20°C compared with the growth temperature in the previous cycle.

[0038] Example 10 Embodiment 10 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Embodiment 1 is that the growth temperature in the current cycle is 30°C higher than the growth temperature in the previous cycle.

[0039] Example 11 Embodiment 11 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Embodiment 1 is that the growth temperature in the current cycle is increased by 40°C compared with the growth temperature in the previous cycle.

[0040] Example 12 Embodiment 12 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Embodiment 1 is that the growth temperature in the current cycle is increased by 50°C compared with the growth temperature in the previous cycle.

[0041] Example 13 Embodiment 13 of the present invention also provides a method for preparing an LED epitaxial wafer. The difference from Embodiment 1 is that the growth temperature in the current cycle is 60°C higher than the growth temperature in the previous cycle.

[0042] Comparative Example 1 Comparative Example 1 also provides a method for preparing an LED epitaxial wafer. The difference from Example 1 is that the three-dimensional growth layer is replaced with a single GaN layer.

[0043] The LED epitaxial wafers from Examples 1 to 13, and Comparative Example 1, were fabricated into Micro-LEDs with dimensions of 15 μm × 30 μm. The test current was 30 mA, and the specific results are as follows:

[0044] The data in the table show that the Micro-LED prepared in Example 1 has the best performance. At this time, the half-width at half-maximum (FWHM) of the XRD (002) and (102) rocking curves reaches the global minimum (65 FWHM, 148 FWHM), indicating that the crystal quality and orientation are optimal. At the same time, the bandwidth reaches the maximum value (1.45 GHz), and the luminous efficiency percentage reaches the highest (100.45%). When the number of cycles is too small (e.g., 1 cycle) or too large (e.g., 7 cycles), the XRD arcseconds increase significantly (the crystal quality deteriorates), the bandwidth decreases significantly, and the luminous efficiency is significantly lower than that of conventional technology (Comparative Example 1).

[0045] In addition, when the temperature gradient is too low (15℃) or too high (60℃), the XRD arcsecond increases sharply and the bandwidth drops drastically, and the luminous efficiency is significantly lower than that of conventional technology (Comparative Example 1); only in the range of 20~50℃, the overall performance is better than conventional, and only slightly lower than the optimal value of 35℃.

[0046] It can be seen that the Micro-LED prepared by the embodiments of the present invention significantly improves the crystal quality and doubles the device bandwidth without sacrificing the operating voltage and luminous brightness, while maintaining or even slightly improving the luminous efficiency, thus taking into account both high-frequency performance and luminous performance.

[0047] In summary, the LED epitaxial wafer fabrication method and Micro-LED in this invention employ a composite segmented growth process to grow a three-dimensional growth layer. AlGaN is grown by utilizing the small size of Al atoms to fill vacancies during GaN growth. Al treatment further fills these vacancies, followed by recrystallization and baking to remove loosely bonded GaN, decomposing it while retaining tightly bonded portions. By gradually increasing the cyclic temperature, the growth process transitions from three-dimensional to two-dimensional, causing defects to annihilate during the transition and significantly reducing defect density. This substantial reduction in defect density suppresses non-radiative recombination and accelerates carrier recombination rates, thereby optimizing the device's electro-optic response speed. It also suppresses the quantum confinement Stark effect (QCSE), increases wavefunction overlap, enhances the radiative recombination rate, and directly improves the modulation bandwidth.

[0048] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are 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 modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing an LED epitaxial wafer, characterized in that, The method includes: The three-dimensional growth layer is prepared using a composite segmented growth method, specifically including: Step 1: Grow a GaN layer using N2 and H2 as carrier gases, while simultaneously introducing NH3 and TMGa. Step 2, grow Al on the GaN layer x Ga (1-x) N layer, where 0 < x < 1. At this time, introduce TMAl based on Step 1; Step 3: Perform Al treatment. At this time, only N2 is retained as the carrier gas, H2 and NH3 are shut off, and only TMAl is passed through. Step 4: Perform recrystallization treatment by introducing N2 and NH3, stopping the introduction of TMAl, and preparing a three-dimensional grown sublayer. By repeating steps one through four, a three-dimensional growth layer composed of several stacked three-dimensional growth sublayers is prepared, wherein the growth temperature in the current cycle is higher than the growth temperature in the previous cycle.

2. The method for preparing an LED epitaxial wafer according to claim 1, characterized in that, The method further includes: Provide a substrate; A buffer layer, the three-dimensional growth 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 are sequentially deposited on the substrate.

3. The method for preparing an LED epitaxial wafer according to claim 1 or 2, characterized in that, The thickness of the three-dimensional growth layer is 400nm~1200nm.

4. The method for preparing an LED epitaxial wafer according to claim 1 or 2, characterized in that, The growth temperature during the first cycle was 900℃~1000℃, and the growth pressure was 100 torr~600 torr.

5. The method for preparing an LED epitaxial wafer according to claim 4, characterized in that, The growth temperature in the current cycle is 20℃~50℃ higher than the growth temperature in the previous cycle, and the number of cycles is 2 to 6.

6. The method for preparing an LED epitaxial wafer according to claim 1 or 2, characterized in that, The thickness of the GaN layer in step one is 100nm~300nm.

7. The method for preparing an LED epitaxial wafer according to claim 1 or 2, characterized in that, Al in step two x Ga (1-x) The thickness of the N layer is 100nm~300nm.

8. The method for preparing an LED epitaxial wafer according to claim 1 or 2, characterized in that, The processing time for the AI ​​process in step three is 10 to 30 seconds.

9. The method for preparing an LED epitaxial wafer according to claim 1 or 2, characterized in that, The recrystallization process in step four takes 10 to 60 seconds.

10. A Micro-LED, characterized in that, The LED epitaxial wafer is prepared according to any one of claims 1-9.

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