A method for preparing a gallium nitride film and a micro-LED device based on a patterned graphene mask

Abstract

This invention discloses a method for fabricating gallium nitride (GaN) thin films and Micro-LED devices based on patterned graphene masks. A graphene layer is obtained by PECVD deposition on a GaN substrate. An etching process is then used to obtain a graphene mask structure pattern with elongated strips or a matrix arrangement of cubes. MOCVD epitaxy is employed, and by changing conditions such as temperature, pressure, and V / III ratio during MOCVD growth, the nucleation of GaN along the steps of the window and mask boundary is effectively controlled. Through lateral epitaxial growth at different times, GaN thin films with low dislocation density and high-performance Micro-LED devices are obtained.

Description

Technical Field

[0001] This invention relates to a method for preparing gallium nitride thin films and Micro-LED devices based on patterned graphene masks, belonging to the field of semiconductor technology. Background Technology

[0002] Gallium nitride (GaN), as one of the representative group III nitride materials, has broad prospects in next-generation lighting displays, mobile communications, and the energy internet due to its large bandgap, high carrier saturation mobility and breakdown field strength, and good thermal conductivity. Since single-crystal GaN is scarce in nature, most commercially available GaN is obtained through heteroepitaxial growth on substrates such as sapphire and silicon carbide. However, the differences in thermal expansion coefficients and lattice constants between different materials directly lead to a deterioration in the crystal quality of the GaN epitaxial layer, resulting in numerous crystal defects such as dislocations and stacking faults. Significant warping can also occur, causing cracking in the epitaxial layer. These defects greatly reduce device performance and severely limit the application and development of GaN. Lateral epitaxial growth (ELOG) is one of the effective methods to reduce dislocation density inside crystals. Common mask materials are mainly amorphous silicon dioxide and silicon nitride. However, these materials are encapsulated inside the material after growth, and their poor thermal and electrical conductivity directly affect the performance of the device. Using two-dimensional materials such as graphene as masks can solve these problems well. Currently, graphene films are mostly obtained by wet transfer, but the obtained graphene films have many defects such as contamination and wrinkles in the material, which will affect the nucleation behavior of GaN, thus preventing the obtaining of high-quality gallium nitride films through lateral epitaxy.

[0003] In GaN display and lighting applications, Micro-LEDs possess a very broad application prospect due to their advantages such as high brightness, low energy consumption, and wide color gamut. Currently, Micro-LED chips of different sizes are mainly obtained through dry etching. However, the device fabrication process inevitably damages the sidewalls of the chip, disrupting the crystal structure and leading to an increase in the non-radiative recombination ratio and a decrease in radiative recombination on the chip surface. This results in a decrease in both internal and external quantum efficiency. Radiative recombination efficiency is mainly affected by factors such as the dislocation density within the material. Dislocations within the material form non-radiative recombination centers, reducing the radiative recombination efficiency of the LED.

[0004] Therefore, there is a need to provide a method that utilizes patterned graphene masks to regulate GaN nucleation, thereby obtaining selectively grown GaN chips and Micro-LED chips with low dislocation density, in order to solve the above problems. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for preparing gallium nitride thin films based on patterned graphene masks to obtain high-quality GaN epitaxial layers, and a method for preparing Micro-LED devices that can effectively reduce dislocation density in different layers of Micro-LEDs and improve device performance.

[0006] The technical solution to achieve the objective of this invention is to provide a method for preparing gallium nitride thin films based on patterned graphene masks, comprising the following steps:

[0007] (1) A graphene layer is obtained by PECVD deposition reaction on a gallium nitride substrate, and a graphene mask structure pattern with long strips or square blocks arranged in a matrix is ​​obtained by etching process.

[0008] (2) Using MOCVD epitaxy, under the conditions of TMGa flux of about 16.1 sccm, NH3 flux of 24-32 slm, V / III of 6000-8000, pressure of 500 Torr, and temperature of 950-970℃, GaN islands are grown by nucleation along the boundaries of blocky or strip-shaped graphene.

[0009] (3) Under the conditions of TMGa flux of 40 sccm, NH3 flux of 80-100 slm, V / III of 8000-10000, pressure of 100-200 Torr, and temperature of 1050-1070℃, the GaN islands growing at the graphene boundary are controlled to grow laterally until they merge, thus obtaining a gallium nitride thin film.

[0010] The present invention also includes a method for fabricating Micro-LED devices based on patterned graphene masks, comprising the following steps:

[0011] (1) A graphene layer was obtained by PECVD deposition on a gallium nitride substrate, and a block-shaped graphene mask structure pattern was obtained by etching process.

[0012] (2) Using MOCVD epitaxy, under the conditions of TMGa flux of about 16.1 sccm, NH3 flux of 24 to 32 slm, V / III of 6000 to 8000, pressure of 500 Torr, and temperature of 950 to 970℃, GaN islands are grown by nucleation along the boundaries of blocky graphene.

[0013] (3) Under the conditions of TMGa flux of 20 sccm, NH3 flux of 40-50 slm, V / III of 8000-10000, pressure of 100-200 Torr, temperature of 1050-1070℃ and growth time of 30-50 min, the GaN islands at the graphene boundary are controlled to grow laterally until they merge, and the graphene is covered under u-GaN to obtain a u-GaN layer with a thickness of 3-5 micrometers.

[0014] (4) Change the growth gas source and deposit n-GaN layer, quantum well layer, AlGaN layer and P-GaN layer in sequence to obtain Micro-LED device.

[0015] The square-shaped mask in the graphene mask structure pattern of the present invention for fabricating Micro-LED devices has a side length of 1 to 5 μm and a spacing of 5 to 30 μm between adjacent square-shaped masks.

[0016] The principle upon which this invention is based is as follows: the graphene mask structure is a square structure perpendicular to the m-plane of GaN. By changing the V / III ratio, the selective nucleation of GaN can be controlled. A higher V / III ratio (about 7000) allows GaN to nucleate along the steps (both sides of the groove) on both sides of the window and the graphene strip, while a lower V / III ratio (about 2000) promotes GaN nucleation in the window region (groove). The combination of the two nucleation methods can effectively achieve selective growth and further merge into a whole GaN strip.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. This invention is based on patterned graphene masks and employs two different epitaxial processes to effectively control the nucleation behavior of GaN, which helps to laterally epitaxially produce high-quality GaN thin films and directly epitaxially produce Micro-LED device structures, avoiding contamination and crystal defects caused during the process.

[0019] 2. The technical solution provided by this invention is that GaN is nucleated at the steps of the graphene mask on both sides of the window. Compared with direct nucleation in the groove of the window, the nucleation method can more effectively reduce the dislocation density in the epitaxial layer.

[0020] 3. This invention utilizes the nucleation property of GaN around patterned graphene to control the growth of independent device structures from GaN. The device structures are obtained through lateral epitaxy, with low dislocation density and good crystal quality. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a strip-shaped graphene mask pattern perpendicular to the m-plane of GaN provided in Embodiment 1 of the present invention;

[0022] Figure 2 This is a schematic diagram illustrating the MOCVD growth principle of GaN nucleation along the window (groove) of a strip-shaped graphene mask using traditional processes.

[0023] Figure 3 The image shows a SEM image of GaN nucleated and grown along the window region of a strip-shaped graphene mask to form an independent strip structure using a conventional process.

[0024] Figure 4 This is a schematic diagram of the MOCVD growth principle of GaN nucleation along the steps of a strip-shaped graphene mask using the process provided in Embodiment 1 of the present invention.

[0025] Figure 5 , 6 Images 7 and 8 are SEM images of GaN nucleated and grown along the steps on both sides of the strip-shaped graphene mask using the process provided in Example 1 of this invention, growing into an independent strip structure, further growing, and growing into a triangular strip.

[0026] Figure 8 The image shows a SEM image of a GaN thin film prepared using the process provided in Example 1 of this invention.

[0027] Figure 9 This is a schematic diagram of the structure of the cube-shaped graphene mask pattern provided in Embodiment 2 of the present invention;

[0028] Figure 10 This is a schematic diagram illustrating the MOCVD growth principle of GaN along a cubic graphene mask using the process provided in Embodiment 2 of the present invention.

[0029] Figure 11 The image shows a SEM image of an independent mesa structure formed by the nucleation and growth of GaN along the steps of a cubic graphene mask using the process provided in Embodiment 2 of this invention.

[0030] Wherein: 1 is the graphene mask, 2 is the gallium nitride template (substrate), 3 is the window (groove), 4 is GaN nucleation in the window region, 5 is GaN further three-dimensional growth based on the nucleation in the window region, 6 is further two-dimensional growth based on the three-dimensional growth, 7 is the finally merged GaN film, 8 is GaN nucleation along the steps of the graphene mask, and 9 is the remaining layer structure of the Micro-LED. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. Example 1

[0032] This embodiment provides a method for preparing a GaN thin film using a strip-patterned graphene mask structure, the steps of which are as follows:

[0033] (1) PECVD growth of graphene

[0034] A graphene layer was obtained by PECVD deposition on a gallium nitride template (substrate);

[0035] (2) Patterned graphene

[0036] The graphene mask substrate structure pattern, arranged in elongated strips, was obtained using an etching process. After organic and inorganic cleaning, photoresist residue, substrate surface oxide layer, and oxide contaminants were removed. (See appendix) Figure 1 This is a schematic diagram of the structure of the graphene mask substrate arranged in a strip shape provided in this embodiment, including a graphene mask 1, a gallium nitride template 2, and a window 3. The graphene mask is a strip pattern mask structure with the strip direction perpendicular to the m-plane of the GaN substrate and a period of 10 μm. The window width is 3 μm and the mask width is 7 μm.

[0037] (3) MOCVD growth of GaN nucleation and GaN thin films

[0038] Using the traditional lateral epitaxial process of MOCVD as a comparative example, see Appendix. Figure 2 This is a schematic diagram illustrating the MOCVD growth principle of GaN nucleation along the window (groove) of a strip-shaped graphene mask using the traditional lateral epitaxy process. Gallium nitride films were grown under conditions of 55 sccm TMGa flux, 28 slm NH3 flux, V / III = 2000, 500 Torr pressure, and 970℃. This allows for controlled GaN nucleation preferentially in the window region. GaN nucleates and grows along the window region of the strip-shaped graphene mask into independent strip structures. See the attached SEM image for the actual product. Figure 3 As shown; under these conditions, three-dimensional growth continued for 60 min until a stable triangular strip structure with {11-22} crystal planes was formed 5. The growth conditions were changed, with TMGa flux of 40 sccm, NH3 flux of 80 slm, V / III=8000, pressure of 200 Torr, and temperature of 1080℃, so that the triangular strips could be further grown in two dimensions 6. After growing for 90 min, they met and merged to form a GaN thin film 7.

[0039] See appendix Figure 4 This diagram illustrates the MOCVD lateral epitaxy process provided in this embodiment, showing the MOCVD growth principle of GaN nucleation along the steps of a strip-shaped graphene mask. Growth was carried out under conditions of 16.1 sccm TMGa flux, 30 slm NH3 flux, V / III = 7500, 500 Torr pressure, and 970℃. GaN nucleation was preferentially controlled at the steps on both sides of the graphene mask. See attached SEM image for the actual object. Figure 5As shown; then, under these conditions, further growth occurs, forming two GaN stripes in the window region, which then merge. See the attached SEM image for the actual product. Figure 6 As shown; after 60 min of growth, a triangular banded structure 5 with {11-22} crystal planes was obtained. See attached SEM image of the actual object. Figure 7 As shown; by changing the growth conditions, with a TMGa flux of 40 sccm, an NH3 flux of 80 slm, V / III = 8000, a pressure of 100 Torr, and a temperature of 1080℃, the triangular strips were further grown in two dimensions. After 80 minutes of growth, they met and merged to form a GaN film. The resulting GaN film, compared to the film obtained using the conventional lateral epitaxy process in the comparative example, exhibited a lower dislocation density, reaching 10-1. 6 cm -2 For the order of magnitude, please refer to the attached SEM image of the actual object. Figure 8 As shown.

[0040] Using the method provided in this embodiment, GaN films of different thicknesses can be obtained by controlling the growth time.

[0041] In this embodiment, MOCVD is used for the first step of GaN nucleation growth at 970℃ and 500 Torr. At this time, dislocations under the mask are completely blocked, and only dislocations in the window region penetrate into the epitaxial layer. The growth parameters are then changed, and the second step of GaN two-dimensional growth is performed at 1070℃ and 100 Torr, which promotes the lateral growth of GaN strips until they merge into a smooth GaN film. Due to the low V / III ratio of the grown sample, GaN nucleation occurs in the grooves, where dislocations penetrating from the window undergo a 90° bend during this process, changing from vertical dislocations to horizontal dislocations. During the merging process, they meet and annihilate, thereby reducing the dislocation density of the epitaxial layer. The method provided by this invention can reduce the dislocation density from 5x10⁻⁶ of the substrate. 8 cm -2 Reduced to 1x10 7 cm -2 This represents a reduction of nearly 1.5 orders of magnitude. Simultaneously, due to the use of samples grown with a high V / III ratio, GaN nucleation occurs at the graphene steps on both sides of the window. Because the contact area between the GaN nucleation islands and the substrate is small, the dislocation density penetrating from the substrate to the epitaxial layer is also lower. Furthermore, these GaN islands further grow into GaN strips, and the narrow strips on both sides of the window immediately meet and merge. Some dislocations in the crystal bend and meet during this process, thus reacting. During lateral growth, dislocations bend at 90°, changing from vertical dislocations to horizontal dislocations, and annihilate each other during merging, further reducing the dislocation density of the epitaxial layer.

[0042] In this embodiment, the selective nucleation of GaN is controlled by changing the V / III ratio. A higher V / III ratio (about 7000) allows GaN to nucleate along the steps (both sides of the groove) on both sides of the graphene strip and the window, while a lower V / III ratio (about 2000) promotes GaN nucleation in the window region (groove). The combination of the two nucleation methods can effectively achieve selective growth (both nucleation methods can reduce the dislocation density of the epitaxial layer, with the first method having a stronger reduction capability), and further merge into a whole GaN strip, finally obtaining a GaN thin film. Example 2

[0043] This embodiment provides a method for fabricating gallium nitride thin films and Micro-LED chips based on cubic graphene mask patterns.

[0044] A graphene layer was obtained by PECVD deposition on a gallium nitride template (substrate); the graphene mask substrate structure pattern was obtained by etching process, see appendix. Figure 9 The diagram below shows a block-shaped graphene mask structure provided in this embodiment, including a graphene mask 1, a gallium nitride template 2, and a window 3. The graphene mask is an array of block-shaped mask structures, with the orientation perpendicular to the m-plane of GaN and parallel to the a-plane, and a period of 10 μm. The dimensions of the window and the mask can be selected according to the actual chip size requirements. In this embodiment, the window width is 7 μm and the mask width is 3 μm.

[0045] After further organic and inorganic cleaning, photoresist residue, substrate surface oxide layer, and oxide contaminants are removed; see appendix. Figure 10 This diagram illustrates the MOCVD growth of GaN along the boundaries of the cubic graphene mask, using the cubic graphene structure provided in this embodiment. Growth was carried out for 5 minutes at a TMGa flux of 16.1 sccm, an NH3 flux of 30 slm, V / III = 7500, a pressure of 500 Torr, and a temperature of 970°C, controlling GaN nucleation preferentially at the steps around the cubic graphene mask. Then, the growth parameters were changed to a TMGa flux of 20 sccm, an NH3 flux of 40 slm, V / III = 8000, a pressure of 200 Torr, and a temperature of 1080°C, allowing the triangular strips to grow further in two dimensions. After 30 minutes of growth, the GaN epitaxial layer completely covered the entire mask, forming a GaN periodic mesa structure with smooth sidewalls. A gallium nitride thin film, u-GaN, was epitaxially generated. See the attached diagram for its SEM image. Figure 11 As shown.

[0046] Growing u-GaN layers under conditions such as 970℃ and a high V / III ratio of 7500℃ enables Ga atoms to acquire extremely strong migration capabilities, thereby forcing Ga atoms to migrate to the steps at the four boundaries of the cubic graphene to react and nucleate, resulting in GaN islands growing along the boundaries. By changing the growth parameters, the GaN islands are encouraged to grow laterally in two dimensions, directly covering the graphene to obtain a complete u-GaN layer.

[0047] In this invention, the graphene mask structure is a square structure perpendicular to the m-plane of GaN. During the first nucleation growth step, a high V / III ratio (approximately 7000) is used to promote GaN nucleation along the steps around the graphene mask and window. Further lateral growth forms a mesa structure of square GaN. This method is more suitable for substrates with smaller mask areas. A smaller mask width facilitates the further merging of GaN islands grown on the surrounding steps. If the mask width is wider, due to the strong migration ability of Ga atoms on the graphene mask, the GaN grown at the mask boundary steps will only further fill the window area. Then, the MOCVD growth gas source is changed, using trimethylgallium, trimethylaluminum, and dicyclopentadienylmagnesium as organometallic compounds. An n-GaN layer, quantum well, AlGaN layer, and p-GaN layer are further grown on this GaN patterned substrate to obtain the basic structure of a micro-LED chip, achieving selective growth of a periodic chip array. Existing technologies using photolithography-etching to obtain Micro-LED chip arrays typically struggle to achieve 5*5μm. 2 In the past, due to exposure issues and other reasons, it was impossible to obtain a pattern structure that met the expected specifications. However, the direct epitaxial growth method provided by this invention can optimize these problems. Furthermore, the array size obtained by direct epitaxy is smaller, and the mask width can be between 500 nm and 5 μm. The chip grown by direct epitaxy has smooth sidewalls and a good crystal structure, which is beneficial for improving the chip's luminous efficiency and thus enhancing device performance.

Claims

1. A method for preparing gallium nitride thin films based on patterned graphene masks, characterized in that... Includes the following steps: (1) A graphene layer is obtained by PECVD deposition reaction on a gallium nitride substrate, and a graphene mask structure pattern with long strips or square blocks arranged in a matrix is ​​obtained by etching process. (2) Using MOCVD epitaxy, under the conditions of TMGa flux of 16.1 sccm, NH3 flux of 24-32 slm, V / III of 6000-8000, pressure of 500 Torr, and temperature of 950-970℃, GaN islands are grown by nucleation along the boundaries of blocky or strip-shaped graphene. (3) Under the conditions of TMGa flux of 40 sccm, NH3 flux of 80-100 slm, V / III of 8000-10000, pressure of 100-200 Torr, and temperature of 1050-1070℃, the GaN islands growing at the graphene boundary are controlled to grow laterally until they merge, thus obtaining a gallium nitride thin film.

2. A method for fabricating Micro-LED devices based on patterned graphene masks, characterized in that... Includes the following steps: (1) A graphene layer was obtained by PECVD deposition on a gallium nitride substrate, and a block-shaped graphene mask structure pattern was obtained by etching process. (2) Using MOCVD epitaxy, under the conditions of TMGa flux of 16.1 sccm, NH3 flux of 24-32 slm, V / III of 6000-8000, pressure of 500 Torr, and temperature of 950-970℃, GaN islands were grown by nucleation along the boundaries of blocky graphene. (3) Under the conditions of TMGa flux of 20 sccm, NH3 flux of 40-50 slm, V / III of 8000-10000, pressure of 100-200 Torr, temperature of 1050-1070℃ and growth time of 30-50 min, the GaN islands at the graphene boundary are controlled to grow laterally until they merge, and the graphene is covered under u-GaN to obtain a u-GaN layer with a thickness of 3-5 micrometers. (4) Change the growth gas source and deposit n-GaN layer, quantum well layer, AlGaN layer and p-GaN layer in sequence to obtain Micro-LED device.

3. The method for fabricating Micro-LED devices based on patterned graphene masks according to claim 2, characterized in that: The square masks in the graphene mask structure pattern have a side length of 1 to 5 μm, and the interval between adjacent square masks is 5 to 30 μm.

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