阅读说明：本技术 生长在石墨烯基板上GaN纳米柱阵列的无损伤转移工艺获得柔性紫外探测器及方法 (Flexible ultraviolet detector and method obtained by nondestructive transfer process of GaN nanorod array grown on graphene substrate ) 是由 李国强 郑昱林 王文樑 唐鑫 陈�胜 杨昱辉 于 2019-10-31 设计创作，主要内容包括：本发明公开了生长在石墨烯基板上GaN纳米柱阵列的无损伤转移工艺获得柔性紫外探测器及方法。该方法先在石墨烯衬底上外延生长GaN纳米柱阵列,得到结构A；再在结构A表面旋涂PMMA并加热固化,得到结构B；接着湿法刻蚀去除结构B的衬底层,得到PMMA/GaN纳米柱阵列/石墨烯复合薄膜,并将其转移至镀上电极结构的柔性衬底上,转移后再旋涂PMMA并加热固化,使得第一层PMMA内部的应力得到释放,实现GaN纳米柱阵列/石墨烯与柔性衬底的完美贴合,防止裂纹和皱褶的出现,最后去除PMMA,得到柔性紫外探测器。本发明实现了紫外探测器的透明化、柔性化,可用于智能穿戴、弯曲显示、柔性传感成像等领域,经济效益可观。(The invention discloses a flexible ultraviolet detector obtained by a nondestructive transfer process of a GaN nanorod array grown on a graphene substrate and a method. According to the method, a GaN nanorod array is epitaxially grown on a graphene substrate to obtain a structure A; spin-coating PMMA on the surface of the structure A and heating and curing to obtain a structure B; and then, removing the substrate layer of the structure B by wet etching to obtain a PMMA/GaN nanorod array/graphene composite film, transferring the PMMA/GaN nanorod array/graphene composite film onto a flexible substrate plated with an electrode structure, spin-coating PMMA and heating for curing after transferring to release the stress in the first layer of PMMA, perfectly attaching the GaN nanorod array/graphene and the flexible substrate, preventing cracks and wrinkles from occurring, and finally removing PMMA to obtain the flexible ultraviolet detector. The invention realizes the transparence and flexibility of the ultraviolet detector, can be used in the fields of intelligent wearing, bending display, flexible sensing imaging and the like, and has considerable economic benefit.)

1. The flexible ultraviolet detector of the GaN nanorod array growing on the graphene substrate is characterized by sequentially comprising a flexible substrate (6), a pair of interdigital electrodes (5) on the flexible substrate, a graphene layer (2) above the interdigital electrodes and the GaN nanorod array (3) growing on the graphene layer (2) from bottom to top.

2. The flexible UV detector of claim 1, wherein the GaN nanorod array is 300 ~ 380 nm in length and 60 ~ 80nm in diameter, and the density of the GaN nanorod array is 5.0 x 10⁹~ 9.0×10⁹/cm²。

3. The method for preparing the flexible ultraviolet detector of the GaN nanorod array grown on the graphene substrate according to any one of claims 1-2, is characterized by comprising the following steps:

(1) placing the graphene substrate in radio frequency assisted molecular beam epitaxy equipment, and growing a GaN nanorod array on the surface of graphene to form a GaN nanorod array/graphene/substrate structure;

(2) spin-coating a layer of polymethyl methacrylate on the surface of the GaN nanorod array obtained in the step (1), and heating and curing to form a PMMA/GaN nanorod array/graphene/substrate structure;

(3) removing the substrate layer with the structure obtained in the step (2) by utilizing a wet etching process to obtain a PMMA/GaN nano-pillar array/graphene composite film, and transferring the PMMA/GaN nano-pillar array/graphene composite film onto a flexible substrate plated with an interdigital electrode structure;

(4) and (4) spin-coating a layer of polymethyl methacrylate on the surface of the PMMA/GaN nanorod array/graphene/electrode flexible substrate transferred in the step (3), heating and curing, washing with deionized water, drying, removing the PMMA on the surface, and drying to obtain the flexible ultraviolet detector of the GaN nanorod array growing on the graphene substrate.

4. The method according to claim 3, wherein in the step (1), the graphene is grown on the copper foil substrate by a general chemical vapor deposition process or is grown on the SiO by a plasma enhanced chemical vapor deposition process₂And/or on a Si substrate.

5. The method according to claim 3, wherein in the step (1), the process conditions for growing the GaN nanorod array on the graphene surface are as follows: firstly, using a mechanical pump and a molecular pump to pump vacuum to the growth cavity, and maintaining the pressure at 2 × 10^-9~4×10^-9Torr, the substrate temperature is raised to 960 ~ 980 ℃, the Ga beam current is accurately measured by the equivalent pressure of the ion beam, and then growth is started, wherein the growth is divided into two steps, firstly, H is firstly introduced₂/N₂Carrying out hydrogenation and nitridation treatment on graphene by using plasma for 3 ~ 4min, wherein H is₂/N₂Setting the flow rate to be (1.0 ~ 1.5.5)/(2.5 ~ 3.0.0) sccm and the power of the RF plasma to be 390 ~ 400W, and stopping the introduction of H₂，N₂The flow rate was set to 2.0 ~ 2.2.2 sccm, the RF plasma power was set to 360 ~ 380W, and then the Ga source beam was turned on, the Ga-BEP was set to 6.5X 10^-8~7.5×10^-8Torr, and the total growth time is 4.0 ~ 4.5.5 h.

6. The method as claimed in claim 3, wherein in the step (2), the PMMA spin coating process comprises the steps of placing the GaN nanorod array/graphene/substrate structure obtained in the step (1) on a turntable of a spin coater, coating the surface of the GaN nanorod array/graphene/substrate structure with 1.6 ~ 1.8.8 wt% PMMA solution, and setting two rotation speeds of 400 rpm and 500rpm at a low speed, 5 ~ 6 s, and 3500 ~ 4000 rpm and 28 ~ 30 s at a high speed, wherein the heating and curing process comprises the steps of heating the GaN nanorod array/graphene/substrate structure at a temperature of 140 ~ 150 ℃ and heating the GaN nanorod array/graphene/substrate structure at a high speed for 2 ~ 3 min.

7. The method according to claim 3, wherein in the step (3), the process for removing the substrate layer of the structure obtained in the step (2) by using a wet etching process is as follows: if grapheneIs prepared by growing on copper foil substrate by common chemical vapor deposition process, etching copper foil with 0.05 ~ 0.06.06 g/ml ferric nitrate solution for 10 ~ 12 h, and performing plasma enhanced chemical vapor deposition process on graphene on SiO₂And etching silicon dioxide on the Si substrate by using B.O.E buffer etching solution for 30 ~ 45 min.

8. The method according to claim 3, wherein in step (3), the interdigital electrode is a layer of Au metal, the thickness of the interdigital electrode is 100 ~ 120 nm, the length of the interdigital electrode is 280 ~ 300 μm, the width of the interdigital electrode is 5 ~ 15 μm, the electrode spacing is 5 ~ 20 μm, and the logarithm is 20 ~ 24 pairs.

9. The method as claimed in claim 3, wherein in the step (4), the PMMA spin coating process is that the PMMA/GaN nanorod array/graphene/electrode flexible substrate transferred in the step (3) is placed on a turntable of a spin coater, the surface of the PMMA/GaN nanorod array/graphene/electrode flexible substrate is coated with 1.6 ~ 1.8wt% PMMA solution, and two steps of rotation speed are set, namely, low speed 400 and 500rpm and 5 ~ 6 s and high speed 3500 ~ 4000 and 4000 rpm and 28 ~ 30 s, and the heating and curing process is that the heating temperature is 95 ~ 100 ℃ and the heating time is 120 ~ 180 min.

10. The method of claim 3, wherein the PMMA is removed in step (4) by soaking and washing in acetone for 5 ~ 6 times for 40 ~ 60 s.

Technical Field

The invention belongs to the field of ultraviolet detectors, and particularly relates to a flexible ultraviolet detector and a method obtained by a nondestructive transfer process of a GaN nanorod array grown on a graphene substrate.

Background

The flexible, bendable and convenient semiconductor optoelectronic device brings revolutionary development to future intelligent wearing, bending display, implantable instruments and the like due to the characteristics of light weight, flexibility, intelligence, high efficiency and the like. Among many optoelectronic devices, as an indispensable component of photoelectric sensing, a UV optical switch or a photodetector has a great application potential in various fields such as visible light communication, industrial automatic control, ultraviolet infrared imaging and the like, and has received special attention from many researchers all over the world over the past decades.

Currently, there is a strong research interest in using low dimensional wide band gap semiconductor nanomaterials, such as GaN, ZnO and other metal oxide nanostructures, to develop flexible UV optical switches or photodetectors with highly enhanced responsivity and photoconductive gain. Among them, GaN one-dimensional nano-array materials have become a hot spot of research in recent years due to their unique nanostructure-induced quantum confinement effects, such as enhanced carrier mobility, excellent light absorption/emission, and almost no dislocation density. On one hand, the huge surface volume ratio of the one-dimensional nano-column obviously increases the light absorption and improves the density of photon-generated carriers. On the other hand, the low dimensional nanostructures limit the active region of charge carriers, shortening the carrier transport time.

Although GaN one-dimensional nanoarrays have great potential, high performance GaN one-dimensional nanoarray-based devices tend to be on rigid, inflexible substrates (e.g., sapphire, silicon, LiAlO)₂MgO, etc.) because of the very high growth temperatures and lattice matched single crystal substrates required for epitaxial growth of such GaN one-dimensional nanoarray-based devices, while the inability to directly epitaxially grow such GaN one-dimensional nanoarrays on flexible substrates (e.g., PET, ITO) severely hampers the rapidly growing requirements of related flexible or wearable applications [ Kuykendall, t., Pauzauskie, p. j., Zhang, y., Goldberger, j., sirbouly, d., Denlinger, j. and Yang, p. crystallographica of high-density gallium nitride nanowire array Nature, 3 (2004) 524-528. doi:10.1038/nmat 7.]。

Disclosure of Invention

In order to overcome the defects and shortcomings of the prior art, the invention aims to provide a flexible ultraviolet detector obtained by a nondestructive transfer process of a GaN nanorod array grown on a graphene substrate and a method. The preparation method has the advantages of simple process, low energy consumption, time saving and high efficiency.

The purpose of the invention is realized by the following technical scheme.

The flexible ultraviolet detector of the GaN nanorod array growing on the graphene substrate sequentially comprises a flexible substrate, a pair of interdigital electrodes on the flexible substrate, a graphene layer above the interdigital electrodes and the GaN nanorod array growing on the graphene layer from bottom to top.

Further, the flexible substrate is a PET, PDMS, or ITO material.

Furthermore, the interdigital electrode is a layer of Au metal, the thickness of the interdigital electrode is 100 ~ 120 nm, the length of the interdigital electrode is 280 ~ 300 mu m, the width of the interdigital electrode is 5 ~ 15 mu m, the electrode spacing is 5 ~ 20 mu m, and the logarithm is 20 ~ 24 pairs.

Further, the GaN nanorod array has a length of 300 ~ 380 nm and a diameter of 60 ~ 80nm, and has a density of 5.0 × 10⁹~ 9.0×10⁹/cm²。

The preparation method of the flexible ultraviolet detector of the GaN nanorod array growing on the graphene substrate comprises the following steps:

(1) placing a graphene substrate in radio frequency assisted molecular beam epitaxy (PA-MBE) equipment, and growing a GaN nanorod array on the surface of graphene to form a GaN nanorod array/graphene/substrate structure;

(2) spin-coating a layer of polymethyl methacrylate (PMMA) on the surface of the GaN nanorod array obtained in the step (1), and heating and curing to form a PMMA/GaN nanorod array/graphene/substrate structure;

(3) removing the substrate layer with the structure obtained in the step (2) by utilizing a wet etching process to obtain a PMMA/GaN nano-pillar array/graphene composite film, and transferring the PMMA/GaN nano-pillar array/graphene composite film onto a flexible substrate plated with an interdigital electrode structure;

(4) and (4) spin-coating a layer of polymethyl methacrylate on the surface of the PMMA/GaN nanorod array/graphene/electrode flexible substrate transferred in the step (3), heating and curing, washing with deionized water, drying, removing the PMMA on the surface, and drying to obtain the flexible ultraviolet detector of the GaN nanorod array growing on the graphene substrate.

Further, in the step (1), the graphene is grown on the copper foil substrate by a general Chemical Vapor Deposition (CVD) process or is grown on the SiO by a Plasma Enhanced Chemical Vapor Deposition (PECVD) process₂And/or on a Si substrate.

Further, in the step (1), the process conditions for growing the GaN nanorod array on the graphene surface are as follows: firstly, using a mechanical pump and a molecular pump to pump vacuum to the growth cavity, and maintaining the pressure at 2 × 10^-9~4×10^-9Torr, the substrate temperature is raised to 960 ~ 980 deg.C, the Ga beam current is accurately measured with the equivalent ion beam pressure (BEP), and then growth is started, the growth is divided into two steps, the first step is firstly introduced with H₂/N₂The plasma carries out hydrogenation and nitridation treatment on the graphene, and the purpose is to open C-C sp of the graphene²Bond, providing more nucleation sites, at a time of 3 ~ 4min, H₂/N₂Setting the flow rate to be (1.0 ~ 1.5.5)/(2.5 ~ 3.0.0) sccm and the power of the RF plasma to be 390 ~ 400W, and stopping the introduction of H₂，N₂The flow rate was set to 2.0 ~ 2.2.2 sccm, the RF plasma power was set to 360 ~ 380W, and then the Ga source beam was turned on, the Ga-BEP was set to 6.5X 10^-8~7.5×10^-8Torr, and the total growth time is 4.0 ~ 4.5.5 h.

Further, in the step (2), the PMMA spin coating process is that the GaN nanorod array/graphene/substrate structure obtained in the step (1) is placed on a rotating disc of a spin coater, 1.6 ~ 1.8wt% of PMMA solution is coated on the surface, and two rotating speeds are set, namely, the low speed is 400-500 rpm, 5 ~ 6 s, and the high speed is 3500 ~ 4000 rpm, 28 ~ 30 s, and the heating and curing process is that the heating temperature is 140 ~ 150 ℃ and the heating time is 2 ~ 3min, so that the GaN nanorod array/graphene/substrate structure is rapidly cured.

Further, in the step (3), the process for removing the substrate layer with the structure obtained in the step (2) by using a wet etching process is that if the graphene is obtained by growing on the copper foil substrate by using a general chemical vapor deposition process, the copper foil is etched by using 0.05 ~ 0.06.06 g/ml ferric nitrate solution for 10 ~ 12 hours, and if the graphene is obtained by using a plasma enhanced chemical vapor deposition process on SiO₂The growth on the Si substrate is carried out by using B.O.E buffered etching solution (49% HF aqueous solution: 40% NH)₄Aqueous F = 1: 6 ~ 7 (volume ratio)) etch silicon dioxide for 30 ~ 45 min.

Further, in the step (4), the PMMA spin coating process is that the PMMA/GaN nanorod array/graphene/electrode flexible substrate transferred in the step (3) is placed on a turntable of a spin coater, 1.6 ~ 1.8.8 wt% of PMMA solution is coated on the surface of the PMMA substrate, two steps of rotating speeds are set, namely, the low speed is 400-500 rpm, the 5 ~ 6 s, and the high speed is 3500 ~ 4000-4000 rpm, and 28 ~ 30 s, the heating and curing process is that the heating temperature is 95 ~ 100 ℃, the heating time is 120 ~ 180 min, and the PMMA substrate is slowly cured, so that the internal stress of the first layer of PMMA is released, the GaN nanorod array/graphene and electrode flexible substrate are perfectly attached, and cracks and wrinkles are prevented.

Further, in the step (4), the PMMA is removed by soaking and cleaning in acetone for 5 ~ 6 times for 40 ~ 60s each time to remove any residual PMMA.

Compared with the prior art, the method has the following advantages and beneficial effects:

(1) the invention discloses a method for obtaining a flexible ultraviolet detector by a nondestructive transfer process of a GaN nanorod array grown on a graphene substrate.

(2) The transfer process provided by the invention uses a two-step PMMA spin coating process, so that the internal stress of PMMA is released, the GaN nanorod array/graphene is perfectly attached to the electrode flexible substrate, cracks and wrinkles are prevented, the appearance of the transferred GaN nanorod array is hardly changed greatly compared with that before the transfer, the transferred GaN nanorod array can be flexibly bent, and the transfer process is completely free of damage.

(3) According to the flexible ultraviolet detector obtained by the nondestructive transfer process of the GaN nanorod array grown on the graphene substrate, on one hand, the characteristics of transparency, conductivity and flexibility of a graphene/GaN nanorod array material are utilized, and the collection and photoelectric response sensitivity of the detector to light is improved; on the other hand, the huge specific surface area and quantum confinement of the one-dimensional nano-column material are utilized, and the density and the transmission time of photon-generated carriers are improved.

(4) The invention realizes the transparence and flexibility of the ultraviolet detector, can be used in the fields of intelligent wearing, bending display, flexible sensing imaging and the like, and has considerable economic benefit.

Drawings

Fig. 1 is a route diagram of a method for obtaining a flexible ultraviolet detector by the nondestructive transfer process of a GaN nanorod array grown on a graphene substrate.

FIG. 2 is a schematic structural diagram of each step of obtaining a flexible ultraviolet detector by the method of the present invention; reference numbers in the figures: 1-copper foil substrate or SiO₂a/Si substrate; 2-graphene; 3-GaN nanorod arrays; 4-PMMA; 5-a metallic Au electrode; 6-flexible substrate.

FIGS. 3a and 3b are SEM micrographs of the GaN nanopillar array surface before and after transfer in example 1.

FIG. 4 is a graph of current I as a function of applied bias voltage V for the flexible UV detector of example 1.

Fig. 5 is a schematic structural diagram of a flexible ultraviolet detector of a GaN nanorod array grown on a graphene substrate according to the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples and drawings, but the present invention is not limited thereto.

In the following specific embodiment, a route diagram of a method for obtaining a flexible ultraviolet detector by a nondestructive transfer process of a GaN nanorod array grown on a graphene substrate is shown in fig. 1. The schematic structural diagram of each step of obtaining the flexible ultraviolet detector by the method of the invention is shown in fig. 2, wherein the structure a is a GaN nano-pillar array/graphene/substrate structure, the structure B is a PMMA/GaN nano-pillar array/graphene/substrate structure, the structure C is a PMMA/GaN nano-pillar array/graphene composite film, and the structure D is a GaN nano-pillar array/graphene flexible ultraviolet detector. The structural schematic diagram of the flexible ultraviolet detector of the GaN nanorod array grown on the graphene substrate is shown in fig. 5, and the flexible ultraviolet detector sequentially comprises a flexible substrate 6, a pair of interdigital electrodes 5 on the flexible substrate, a graphene layer 2 above the interdigital electrodes, and a GaN nanorod array 3 grown on the graphene layer 2 from bottom to top.