A nitrogen-polar GaN-based long-wavelength LED chip on graphene and a preparation method thereof

Abstract

A nitrogen-polar GaN-based long-wavelength LED chip on graphite and its manufacturing method, belonging to the field of semiconductor light-emitting devices. It consists of a substrate layer, a graphene layer, a nitrogen-polar GaN template layer, a nitrogen-polar n-GaN electron supply layer, a nitrogen-polar InGaN-based quantum well active region, a nitrogen-polar p-Al x1 Ga 1‑x1 GaN electron blocking layer, a nitrogen-polar p-GaN hole injection layer, a p-type electrode layer, and an n-type electrode layer. The interaction force between the graphene and the epitaxial film is weak, the stress on the quantum well active region will be reduced, and at the same time, the warpage of the epitaxial wafer will be reduced, which can improve the indium incorporation efficiency in the quantum well layer, relieve phase separation, and improve the light emission uniformity. In addition, the use of a nitrogen-polar InGaN quantum well structure can further improve the indium incorporation efficiency. Therefore, based on nitrogen-polar materials on graphene, the epitaxial growth of the quantum well can be achieved at a higher temperature, thereby improving the crystal quality of the quantum well.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor light-emitting devices, and in particular relates to a nitrogen-polarity GaN-based long-wavelength LED chip on graphene and a preparation method thereof. Background Art

[0002] At present, compared with GaN-based blue LEDs, GaN-based long-wavelength LEDs, especially GaN-based red LEDs, have low luminous efficiency. The main reason is that the luminous efficiency of the InGaN-based quantum well structure in the active region of the LED is low, and the low luminous efficiency of the quantum well structure is related to the high indium component required in the InGaN well layer: First, to achieve a high indium component, the InGaN quantum well needs to be grown at a lower temperature, and the low growth temperature leads to poor crystal quality of the InGaN quantum well. At the same time, in order to prevent the thermal decomposition of indium in the InGaN quantum well, the growth temperature of the GaN or InGaN barrier layer cannot be too high, which makes the crystal quality of the quantum barrier layer poor; second, the high indium component makes the lattice mismatch between the InGaN well layer and the barrier layer larger, so that the stress on the InGaN well layer is also large, which will reduce the incorporation efficiency of indium in the InGaN well layer and aggravate the phase separation and quantum confinement Stark effect. At the same time, the reduction in indium incorporation efficiency will further reduce the growth temperature of the quantum well. In addition, the large residual stress of the InGaN well layer will induce new dislocations at the interface between the well layer and the barrier layer, reducing the crystal quality of the quantum well. The low luminous efficiency of GaN-based long-wavelength LEDs has greatly hindered the development of GaN-based full-color display technology and micro-display technology. Summary of the invention

[0003] The purpose of the present invention is to solve the problem of low luminous efficiency of the above-mentioned GaN-based long-wavelength LED, and to prepare a nitrogen-polar GaN-based long-wavelength LED chip on graphene by comprehensively considering aspects such as improving the crystal quality of the epitaxial layer and the quantum well growth temperature and improving device performance.

[0004] Its advantages are: the graphene surface lacks dangling bonds, the interaction force between it and the epitaxial GaN is weak, the interface GaN lattice constant will not be as strained as traditional heteroepitaxial, the stress on the film will be reduced, and the warping of the epitaxial wafer can be effectively prevented, which is very beneficial to improve the incorporation efficiency and luminescence uniformity of the InGaN quantum well structure on it, and at the same time it is beneficial to improve the crystal quality of the quantum well structure, and is suitable for the epitaxial growth of the InGaN-based long-wavelength quantum well structure with a high indium component. In addition, the low residual stress in the epitaxial GaN film reduces the dislocation density induced by stress, which can further improve the crystal quality of the long-wavelength quantum well structure and improve the luminescence efficiency of the long-wavelength quantum well structure. In addition, compared with traditional metal polar materials, the incorporation efficiency of indium in nitrogen polar InGaN is higher, and epitaxial growth can be achieved at a higher temperature. Since the incorporation efficiency of indium in the InGaN quantum well structure can also be improved based on graphene, the epitaxial growth of the InGaN-based long-wavelength quantum well with a high indium component can be achieved at a higher temperature based on nitrogen polar materials on graphene. At the same time, the increase in the quantum well growth temperature can correspondingly increase the growth temperature of the quantum barrier layer, thereby improving the overall crystal quality of the quantum well structure and improving the luminescence characteristics of the long-wavelength quantum well structure. Therefore, the present invention can obtain an efficient GaN-based long-wavelength LED chip.

[0005] The present invention designs a nitrogen-polar GaN-based long-wavelength LED chip on graphene (see attached Figure 1 , from bottom to top, a substrate 1, a graphene layer 2, a nitrogen-polar GaN template layer 3, a nitrogen-polar n-GaN electron supply layer 4, a nitrogen-polar InGaN-based multi-quantum well active region 5, a nitrogen-polar p-Al x1 Ga 1-x1 The substrate 1 is composed of a N electron barrier layer 6 and a nitrogen polarity p-GaN hole injection layer 7, a bare nitrogen polarity n-GaN electron supply layer 4 table is formed between the nitrogen polarity n-GaN electron supply layer 4 and the nitrogen polarity InGaN-based multi-quantum well active region 5, and an n-type electrode layer 9 and a p-type electrode layer 8 are prepared on the nitrogen polarity n-GaN electron supply layer 4 table and the nitrogen polarity p-GaN hole injection layer 7, respectively; wherein 0.1≤x1≤0.4. The substrate 1 can be any substrate that can grow a nitrogen polarity nitride layer, such as a carbon surface silicon carbide substrate, a nitrogen surface GaN substrate, a sapphire substrate treated with ammonia at high temperature (treated at 1000-1100°C for 5-10 minutes).

[0006] The above-mentioned nitrogen-polar GaN-based long-wavelength LED chip on graphene comprises a GaN template layer 3, an n-GaN electron supply layer 4, an InGaN-based multi-quantum well active region 5, and a p-Al x1 Ga 1-x1The N electron blocking layer 6 and the p-GaN hole injection layer 7 are both nitrogen polar. Nitrogen polar nitride semiconductor has a hexagonal wurtzite structure, and its c-axis <0001> The direction is asymmetric, that is, the positive charge center of the metal atom and the negative charge center of the nitrogen atom along the c-axis do not coincide, and there is a spontaneous polarization effect. When the nitride material grows along the c-axis, when the bonding direction of the metal atoms and nitrogen atoms parallel to the c-axis along the growth direction is the metal atom pointing to the nitrogen atom, the lattice polarity of the material is metal polarity. Conversely, if the bonding direction of the metal atoms and nitrogen atoms parallel to the c-axis along the growth direction is the nitrogen atom pointing to the metal atom, the polarity of the material is nitrogen polarity. The polarization directions in nitrogen-polar nitride materials and metal-polar nitride materials are opposite, so the polarization electric fields along the growth direction in these two polar materials are opposite. The method for obtaining a nitrogen-polar nitride layer is related to the substrate and the surface treatment process of the substrate. For example, a nitrogen-polar nitride layer can be directly grown on a carbon-faced silicon carbide substrate and a nitrogen-faced GaN substrate, and a nitrogen-polar nitride layer can also be grown on a sapphire substrate treated with high-temperature ammonia (i.e., by introducing ammonia gas at a high temperature of 1000-1100°C for 5-10 minutes).

[0007] In the above-mentioned nitrogen-polarity GaN-based long-wavelength LED chip on graphene, the nitrogen-polarity InGaN quantum well active layer region 5 is composed of a barrier layer In y0 Ga 1-y0 N and well layer In x0 Ga 1-x0 N alternate growth patterns, the number of pairs is between 2 and 5, where 0.25<x0≤1, 0≤y0<x0.

[0008] In the above-mentioned nitrogen-polarity GaN-based long-wavelength LED chip on graphene, the thickness of the nitrogen-polarity GaN template layer 3 is 500nm-5μm, the thickness of the nitrogen-polarity n-GaN electron supply layer 4 is 500nm-3μm, the thickness of each barrier layer GaN in the nitrogen-polarity InGaN-based multi-quantum well active region 5 is 10-15nm, and the thickness of each well layer InGaN is 100nm-150nm. x0 Ga 1-x0 The thickness of N is 2 to 4 nm, and the nitrogen polar p-Al x1 Ga 1-x1 The thickness of the N electron blocking layer 6 is 10 to 40 nm, the thickness of the nitrogen polar p-GaN hole injection layer 7 is 100 to 200 nm, the thickness of the p-type electrode layer 8 is 5 to 100 nm, and the thickness of the n-type electrode layer 9 is 5 to 100 nm.

[0009] In the above-mentioned nitrogen-polar GaN-based long-wavelength LED chip on graphene, the p-type electrode can be a single layer of a mono-alloy such as Au, Pt, a binary alloy composite layer such as Ni-Au, Ni-Pt, or a ternary alloy composite layer such as Ti-Pt-Au, Ni-Pt-Au, etc., and the n-type electrode can be a binary alloy composite layer such as Ti-Al, a ternary alloy composite layer such as Ti-Al-Au, or a quaternary alloy composite layer such as Ti-Al-Ni-Au.

[0010] A method for preparing the above-mentioned nitrogen-polar GaN-based long-wavelength LED chip on graphene, the steps of which are as follows:

[0011] (1) directly preparing a graphene layer 2 on a substrate 1 or transferring the graphene layer 2 to the substrate 1;

[0012] One feasible method for directly preparing graphene on a substrate is: annealing the substrate (especially a carbon-surfaced silicon carbide substrate) at 800-1000° C. for 1-2 hours in an argon atmosphere, with an annealing pressure of 200-400 mbar; then, heating the substrate to 1500-1700° C. for 2-4 hours in an argon atmosphere at 600-800 mbar to achieve the growth of a graphene layer on the substrate surface;

[0013] One feasible method for transferring the graphene layer 2 to the substrate 1 is: spin-coat photoresist on the surface of the graphene deposited on the copper sheet by chemical vapor deposition, and then dissolve the copper sheet in a solution, so that the photoresist and graphene are combined together; further, transfer the photoresist and graphene into an aqueous solution, then place the substrate at the bottom of the aqueous solution and directly pick it up, and finally remove the photoresist with an organic solvent, thereby realizing the transfer of the graphene layer 2.

[0014] (2) A nitrogen-polar GaN template layer 3, a nitrogen-polar n-GaN electron supply layer 4, a nitrogen-polar InGaN-based multi-quantum well active region 5, a nitrogen-polar p-Al2O3 active region 6, and a graphene layer 2 are sequentially grown on the graphene layer 2 by metal organic vapor phase epitaxy (MOCVD) or molecular beam epitaxy. x1 Ga 1-x1 N electron blocking layer 6, nitrogen polar p-GaN hole injection layer 7, thereby preparing a nitrogen polar GaN-based long wavelength LED structure on graphene; the growth source is trimethylaluminum, trimethylindium, triethylgallium, trimethylgallium and high-purity ammonia, the growth temperature is 500-1100°C, the growth pressure is 100-400mbar, and silane and dicyclopentadienyl magnesium are used for n-type and p-type doping respectively, and the doping concentration is 10 17 ~10 20 / cm 3 ;

[0015] (3) The area on one side of the upper surface of the nitrogen-polarity p-GaN hole injection layer 7 is etched by ICP method until the nitrogen-polarity n-GaN electron supply layer 4 is exposed to obtain the nitrogen-polarity n-GaN table; a p-type electrode layer 8 (thickness 5 to 100 nm) is prepared on the unetched nitrogen-polarity p-GaN hole injection layer 7, and an n-type electrode layer 9 (thickness 5 to 100 nm; the p-type electrode is a metal deposited on the p-type layer, called the p-type electrode; the n-type electrode is a metal deposited on the n-type layer, called the n-type electrode); the method for preparing the electrode can adopt thermal evaporation, electron beam evaporation or magnetron sputtering method, so as to prepare the nitrogen-polarity GaN-based long-wavelength LED chip on graphene.

[0016] Effects and benefits of the present invention: The graphene surface lacks dangling bonds, and the interaction force between the graphene and the epitaxial GaN is weak. The interface GaN lattice constant will not be strained as much as in traditional heteroepitaxial growth, and the stress on the film will be reduced, which can effectively prevent the warping of the epitaxial wafer, which is very beneficial to improving the incorporation efficiency and luminescence uniformity of the InGaN quantum well structure thereon, and is also beneficial to improving the crystal quality of the quantum well structure, and is suitable for the epitaxial growth of a high indium component InGaN-based long-wavelength quantum well structure. In addition, the low residual stress in the epitaxial GaN film reduces the dislocation density induced by stress, which can further improve the crystal quality of the long-wavelength quantum well structure and improve the luminescence efficiency of the long-wavelength quantum well structure. In addition, compared with traditional metal polar materials, the incorporation efficiency of indium in nitrogen polar InGaN is higher, and epitaxial growth can be achieved at a higher temperature. Since the incorporation efficiency of indium in the InGaN quantum well structure can also be improved based on graphene, the epitaxial growth of a high indium component InGaN-based long-wavelength quantum well can be achieved at a higher temperature based on nitrogen polar materials on graphene. At the same time, the increase in the quantum well growth temperature can correspondingly increase the growth temperature of the quantum barrier layer, thereby improving the overall crystal quality of the quantum well structure and improving the luminescence characteristics of the long-wavelength quantum well structure. The method of the present invention can obtain an efficient nitrogen-polarity GaN-based long-wavelength LED chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : A schematic diagram of the structure of the nitrogen-polar GaN-based long-wavelength LED chip on graphene according to the present invention;

[0018] Figure 2 : Photoluminescence spectra of the nitrogen-polar GaN-based long-wavelength LED on graphene in Example 1 and the reference LED (without graphene layer 2).

[0019] The names of the parts in the figure are: substrate 1, graphene layer 2, nitrogen-polar GaN template layer 3, nitrogen-polar n-GaN electron supply layer 4, nitrogen-polar InGaN-based multi-quantum well active region 5, nitrogen-polar p-Al x1 Ga1-x1 N electron blocking layer 6 , nitrogen polar p-GaN hole injection layer 7 , p-type electrode layer 8 , and n-type electrode layer 9 . DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention are described in detail below in combination with the technical solutions and the accompanying drawings.

[0021] Embodiment 1:

[0022] 1. Anneal the carbon-surfaced silicon carbide substrate 1 at 1000°C for 2 hours in an argon atmosphere with an annealing pressure of 400 mbar; then, continue to heat to 1700°C in an argon atmosphere at 800 mbar for 3 hours to achieve the growth of a graphene layer 2 on the surface of the carbon-surfaced silicon carbide substrate 1. Then, use the MOCVD method to epitaxially prepare a nitrogen-polar InGaN-based LED structure on the graphene layer 2 at one time, such as Figure 1 The specific structure is as follows: a nitrogen-polar GaN template layer 3 (thickness 1.5 μm), a nitrogen-polar n-GaN electron supply layer 4 (thickness 1.5 μm, doping concentration 3×10 18 / cm 3 ), nitrogen-polarity InGaN-based quantum well active region 5 (the number of quantum well pairs is 5, i.e., barrier / well / barrier / well layer structure, the barrier layer is GaN, with a thickness of 12nm; the well layer is In 0.3 Ga 0.7 N, thickness 2nm), nitrogen polar p-Al 0.3 Ga 0.7 N electron blocking layer 6 (thickness 20nm, doping concentration 3×10 20 / cm 3 ), nitrogen-polar p-GaN hole injection layer 7 (thickness 150nm, doping concentration 5×10 20 / cm 3 The growth sources are trimethylaluminum, trimethylindium, triethylgallium, trimethylgallium and high-purity ammonia. Silane and bismuth magnesium are used for n-type and p-type doping respectively. The growth temperature of the nitrogen-polar GaN template layer 3 and the nitrogen-polar n-GaN electron supply layer 4 is 1080°C and the reaction pressure is 100mbar; the reaction pressure of the nitrogen-polar InGaN-based quantum well active region 5 is 400mbar, and the growth temperatures of the barrier layer GaN and the well layer InGaN are 820°C and 750°C respectively; the nitrogen-polar p-Al 0.3 Ga 0.7 The growth temperature of the N electron blocking layer 6 and the nitrogen polar p-GaN hole injection layer 7 are both 980° C., and the reaction pressures are 100 mbar and 150 mbar, respectively. The specific growth parameters of each layer of the device are shown in Table 1.

[0023] Table 1: Growth parameters of each layer of nitrogen-polar GaN-based long-wavelength LED on graphene

[0024]

[0025] Table 1 Notes: TMGa stands for trimethylgallium; TEGa stands for triethylgallium; TMIn stands for trimethylindium; TMAl stands for trimethylaluminum;

[0026] Cp 2 Mg represents magnesium cyclopentadienyl; SiH 4 stands for silane; NH 3 Stands for high purity ammonia.

[0027] 2. The area on one side of the upper surface of the nitrogen-polarity p-GaN hole injection layer 7 was etched by ICP method (the etching gas was chlorine and boron chloride with a flow ratio of 9:1, and the plate power was 100W) until the nitrogen-polarity n-GaN electron supply layer 4 was exposed to obtain the nitrogen-polarity n-GaN table; the p-type electrode layer 8 of Ni-Au binary alloy composite material (thickness 60nm, Ni layer thickness 30nm, Au layer thickness 30nm, evaporation sources were Ni metal and Au metal respectively) was prepared on the unetched nitrogen-polarity p-GaN hole injection layer 7 by thermal evaporation method, and the n-type electrode layer 9 of Ti-Al binary alloy composite material (thickness 120nm, Ti layer thickness 20nm, Al layer thickness 100nm, evaporation sources were Ti metal and Al metal respectively) was prepared on the exposed nitrogen-polarity n-GaN electron supply layer 4 table, thereby obtaining a nitrogen-polarity GaN-based long-wavelength LED chip on graphene. The specific preparation process of the electrode is shown in Table 2.

[0028] For comparison, we prepared another reference LED sample directly on a carbon-surface SiC substrate (the SiC substrate was not treated by thermal sublimation and had no graphene layer on the surface) using the same epitaxial structure and growth conditions.

[0029] Table 2: Device electrode preparation process parameters

[0030]

[0031] Figure 2 The photoluminescence spectra of the nitrogen-polarity GaN-based long-wavelength LED on graphene and the reference LED in Example 1 show that the peak emission wavelength of the nitrogen-polarity GaN-based long-wavelength LED on graphene is 537nm, which is 75nm red-shifted compared to the reference LED (emission wavelength 462nm), indicating that the incorporation efficiency of indium in the nitrogen-polarity InGaN-based quantum well on graphene is higher. For nitride LEDs, their luminous efficiency will gradually decrease with the increase of emission wavelength, but from Figure 2It can be seen that although the nitrogen-polar GaN-based long-wavelength LED on graphene has a longer emission wavelength, its luminous intensity is not reduced compared with the reference LED with a short emission wavelength, which shows that the combination of graphene and nitrogen-polar materials is conducive to the preparation of high-performance long-wavelength LEDs.

Claims

1. A nitrogen-polar GaN-based long-wavelength LED chip on graphene, characterized in that: From bottom to top, it consists of a substrate (1), a graphene layer (2), a nitrogen-polar GaN template layer (3), a nitrogen-polar n-GaN electron supply layer (4), a nitrogen-polar InGaN-based multi-quantum well active region (5), a nitrogen-polar p-Al x1 Ga 1-x1 The invention relates to a method for manufacturing a nitrogen-polarity n-GaN multi-quantum well active region (5) comprising a nitrogen-polarity n-GaN electron supply layer (4) and a nitrogen-polarity p-GaN hole injection layer (7); a bare nitrogen-polarity n-GaN electron supply layer (4) table is formed between the nitrogen-polarity n-GaN electron supply layer (4) and the nitrogen-polarity InGaN multi-quantum well active region (5); an n-type electrode layer (9) and a p-type electrode layer (8) are respectively prepared on the nitrogen-polarity n-GaN electron supply layer (4) table and the nitrogen-polarity p-GaN hole injection layer (7); the nitrogen-polarity InGaN quantum well active layer region (5) is formed by a barrier layer InGaN. y0 Ga 1-y0 N and well layer In x0 Ga 1-x0 N alternate growth composition, the number of growth pairs is between 2 and 5, wherein 0.1≤x1≤0.4, 0.25<x0≤1, 0≤y0<x0; wherein the graphene layer (2) increases the In component in the epitaxial nitrogen-polar InGaN quantum well, thereby obtaining a highly efficient nitrogen-polar high-In component InGaN long-wavelength LED chip.

2. The nitrogen-polar GaN-based long-wavelength LED chip on graphene as claimed in claim 1, characterized in that: The substrate (1) is a carbon-surface silicon carbide substrate, a nitrogen-surface GaN substrate, or a sapphire substrate treated with ammonia at high temperature.

3. The nitrogen-polar GaN-based long-wavelength LED chip on graphene as claimed in claim 1, characterized in that: The thickness of the nitrogen-polar GaN template layer (3) is 500 nm to 5 μm, the thickness of the nitrogen-polar n-GaN electron supply layer (4) is 500 nm to 3 μm; each well layer InGaN-based multi-quantum well active region (5) has a thickness of 100 nm to 300 μm. x0 Ga 1-x0 The thickness of N is 2~4 nm, 0<x0≤1; each barrier layer In y0 Ga 1-y0 The thickness of N is 10~15 nm, 0≤y0<x0; nitrogen polar p-Al x1 Ga 1-x1 The thickness of the N electron blocking layer (6) is 10-40 nm, the thickness of the nitrogen polar p-GaN hole injection layer (7) is 100-200 nm, the thickness of the p-type electrode layer (8) is 5-100 nm, and the thickness of the n-type electrode layer (9) is 5-100 nm.

4. The nitrogen-polar GaN-based long-wavelength LED chip on graphene as claimed in claim 1, characterized in that: The p-type electrode layer (8) is a single alloy layer, a binary alloy composite layer or a ternary alloy composite layer of Au, Pt, Ni-Au, Ni-P, Ti-Pt-Au or Ni-Pt-Au, and the n-type electrode is a binary alloy composite layer, a ternary alloy composite layer or a quaternary alloy composite layer of Ti-Al, Ti-Al-Au or Ti-Al-Ni-Au.

5. A method for preparing a nitrogen-polar GaN-based long-wavelength LED chip on graphene according to any one of claims 1 to 4, wherein the steps are as follows: (1) directly preparing a graphene layer (2) on a substrate (1) or transferring the graphene layer (2) onto a substrate (1); (2) on the graphene layer (2), a nitrogen-polar GaN template layer (3), a nitrogen-polar n-GaN electron supply layer (4), a nitrogen-polar InGaN-based multi-quantum well active region (5), a nitrogen-polar p-Al x1 Ga 1-x1 N electron blocking layer (6), nitrogen polar p-GaN hole injection layer (7), thereby preparing a nitrogen polar GaN-based long wavelength LED structure on graphene; the growth source is trimethylaluminum, trimethylindium, triethylgallium, trimethylgallium and high-purity ammonia, the growth temperature is 500~1100°C, the growth pressure is 100~400 mbar, and silane and dicyclopentadienyl magnesium are used for n-type and p-type doping respectively, and the doping concentration is 10 17 ~10 20 / cm 3 ; (3) The area on one side of the upper surface of the nitrogen-polarity p-GaN hole injection layer (7) is etched by an ICP method until the nitrogen-polarity n-GaN electron supply layer (4) is exposed, thereby obtaining a nitrogen-polarity n-GaN table; a p-type electrode layer (8) is prepared on the unetched nitrogen-polarity p-GaN hole injection layer (7), and an n-type electrode layer (9) is prepared on the exposed nitrogen-polarity n-GaN table, thereby obtaining the nitrogen-polarity GaN-based long-wavelength LED chip on graphene.

6. The method for preparing a nitrogen-polar GaN-based long-wavelength LED chip on graphene as claimed in claim 5, characterized in that: The graphene layer (2) is directly prepared on the substrate (1) by annealing the substrate (1) at 800-1000°C for 1-2 hours in an argon atmosphere, with an annealing pressure of 200-400 mbar; and then continuing to heat to 1500-1700°C in an argon atmosphere at 600-800 mbar for 2-4 hours, thereby achieving the growth of the graphene layer (2) on the surface of the substrate (1).

7. The method for preparing a nitrogen-polar GaN-based long-wavelength LED chip on graphene as claimed in claim 5, characterized in that: The graphene layer (2) is transferred to the substrate (1) by depositing graphene on a copper sheet by chemical vapor deposition, then spin-coating a photoresist on the surface of the copper sheet, and then dissolving the copper sheet in a solution, thereby combining the photoresist and the graphene together; then the photoresist and the graphene are transferred to an aqueous solution, the substrate is placed at the bottom of the aqueous solution and directly scooped up, and finally the photoresist is removed with an organic solvent, thereby achieving the transfer of the graphene layer (2).

8. The method for preparing a nitrogen-polar GaN-based long-wavelength LED chip on graphene as claimed in claim 5, characterized in that: The method for preparing the electrode is thermal evaporation, electron beam evaporation or magnetron sputtering.

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