Visible blind infrared detector and preparation method thereof

Abstract

The invention belongs to the technical field of photoelectric detectors, and particularly relates to a visible blind infrared detector and a preparation method thereof. The invention provides a visible blind infrared detector. The visible blind infrared detector comprises a substrate; the buffer layer is arranged on the upper surface of the substrate; the vertical nanowire array is arranged on the upper surface of the buffer layer; the filling layer is arranged in a gap of the vertical nanowire array, and the thickness of the filling layer is the same as the height of the vertical nanowire array; and the transparent electrode is arranged on the upper surfaces of the vertical nanowire array and the filling layer. According to the invention, an additional optical filter is not needed, the collection efficiency of photo-generated non-equilibrium carriers in a vertical nanowire channel is regulated and controlled by utilizing a nanowire array resonance absorption effect, and the light response in a near-infrared band range is enhanced by introducing a nanowire-substrate interface trap state and utilizing a photo-induced grid-control effect, so that efficient visible blind infrared detection is realized; and the preparation method has the advantages of high stability and simple preparation process.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectric detectors, and in particular relates to a visible blind infrared detector and a preparation method thereof. Background Art

[0002] Photodetectors convert optical signals into electrical signals and are widely used in various fields such as environmental monitoring, information communication, autonomous driving and medical diagnosis. Photodetectors can be divided into broadband and narrowband (or spectrally selective) categories according to their spectral response characteristics. In applications involving monochromatic light detection and imaging systems, such as facial recognition, iris recognition, biosensing and all-weather robots, narrowband photodetectors are generally superior to broadband photodetectors. This is mainly because broadband photodetectors can generate photoelectric signals under light excitation across the entire response spectrum (covering wavelengths from ultraviolet to infrared), so they are extremely susceptible to ambient light or background light in monochromatic light detection applications, resulting in signal distortion. Among narrowband photodetectors, the most representative type is the visible-blind infrared photodetector, which can only respond to incident light of a specific wavelength in the infrared band, and almost shows no light response to incident light in the visible light band.

[0003] Currently, commercial visible-blind infrared photodetectors are usually realized by coupling broadband photodetectors with filters. However, this approach not only increases the structural complexity but also increases the preparation cost. In addition, the use of filtering optical systems introduces additional optical interfaces, which inevitably reduce image clarity and cause signal crosstalk, making it challenging to achieve higher pixel density in imaging systems.

[0004] To address this problem, methods for preparing visible blind infrared detectors that do not require additional filters have emerged in recent years, including: 1) using photosensitive materials with narrow spectral absorption for narrow-band detection; 2) introducing charge collection narrowing methods to regulate the carrier collection efficiency of different incident light excitations; 3) designing exciton dissociation narrowing schemes to regulate the exciton dissociation efficiency, etc. However, the visible blind detectors prepared by these methods are usually based on organic semiconductors or organic-inorganic hybrid semiconductor materials. Although these materials have the characteristics of low cost and flexibility, they are poor in stability. Summary of the invention

[0005] The objective of the present invention is to provide a visible blind infrared detector and a preparation method thereof. The visible blind infrared detector provided by the present invention can realize spectrally selective infrared detection without the need for an additional filtering system and has the advantages of high stability and low process complexity.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a visible blind infrared detector, comprising a substrate; a buffer layer arranged on the upper surface of the substrate; a vertical nanowire array arranged on the upper surface of the buffer layer; a filling layer arranged in the gaps of the vertical nanowire array, the thickness of the filling layer being the same as the height of the vertical nanowire array; and a transparent electrode arranged on the upper surfaces of the vertical nanowire array and the filling layer.

[0007] Preferably, the material of the vertical nanowire array includes one or more of GaAs, InP and InGaAs.

[0008] Preferably, the height of the vertical nanowire array is 3-4 μm.

[0009] Preferably, the material of the filling layer is a thermosetting polymer, and the thermosetting polymer includes photoresist and / or benzocyclobutene.

[0010] Preferably, the material of the substrate is GaAs.

[0011] Preferably, the material of the buffer layer is heavily doped GaAs; and the thickness of the buffer layer is 5-10 nm.

[0012] Preferably, the transparent electrode is an indium tin oxide transparent electrode or a gallium-doped zinc oxide transparent electrode; the thickness of the transparent electrode is 100-200 nm.

[0013] The present invention provides a method for preparing the visible blind infrared detector described in the above technical solution, comprising the following steps: Preparing a buffer layer on the upper surface of the substrate; preparing a vertical nanowire array on the upper surface of the buffer layer; preparing a filling layer in the gaps of the vertical nanowire array; Transparent electrodes are prepared on the upper surfaces of the vertical nanowire array and the filling layer.

[0014] Preferably, the vertical nanowire array is prepared by a molecular beam epitaxy method based on a metal autocatalytic growth method; The preparation conditions of the vertical nanowire array include: V / III ratio of 15-20:1, substrate temperature of 450-480°C, and growth time of 1.5-2.5 hours.

[0015] Preferably, the method for preparing the filling layer comprises the following steps: Filling the gaps of the vertical nanowire array with a thermosetting polymer, and then performing thermal curing to obtain the filling layer; the filling method of the thermosetting polymer is spin coating, the spin coating speed is 1500-2000 r / s, and the time is 40-50s; the thermal curing temperature is 65-70°C, and the time is ≥12h; The preparation method of the transparent electrode is a dual ion beam sputtering method combined with a hard mask method; the preparation conditions of the transparent electrode include: a deposition rate of 5-8 nm / min.

[0016] The present invention provides a visible blind infrared detector, comprising a substrate; a buffer layer arranged on the upper surface of the substrate; a vertical nanowire array arranged on the upper surface of the buffer layer; a filling layer arranged in the gap of the vertical nanowire array, the thickness of the filling layer being the same as the height of the vertical nanowire array; and a transparent electrode arranged on the upper surface of the vertical nanowire array and the filling layer. In the present invention, the vertical nanowire array arranged on the upper surface of the buffer layer is a quasi-one-dimensional nanowire vertical array, which has an inherent chromatic aberration effect, that is, the spatial positions of light absorption of incident light of different wavelength bands are naturally separated. Specifically, as the incident light band moves toward a long wavelength, the depth of downward propagation of electromagnetic wave energy distributed in the vertical channel of a single nanowire can extend to the order of several microns, far exceeding the carrier diffusion length. This feature provides design freedom for adjusting the collection of photogenerated non-equilibrium carriers excited by incident light of different energies. In addition, the natural quasi-one-dimensional structure of the nanowire provides a high-speed transport channel for carriers and has a large surface area to volume ratio, thereby providing the possibility of achieving high photoelectric gain, the so-called light-induced gating effect. Therefore, the present invention does not require additional filters, and uses the resonant absorption effect of the nanowire array to regulate the collection efficiency of photogenerated non-equilibrium carriers in the vertical nanowire channel. By introducing nanowire-substrate interface trap states, the light-induced gating effect is used to enhance the light response in the near-infrared band, thereby achieving efficient visible blind infrared detection, and has the advantages of high stability and simple preparation process.

[0017] The present invention provides a method for preparing a visible blind infrared detector as described in the above technical solution, comprising the following steps: preparing a buffer layer on the upper surface of the substrate; preparing a vertical nanowire array on the upper surface of the buffer layer; preparing a filling layer in the gaps of the vertical nanowire array; and preparing a transparent electrode on the upper surface of the vertical nanowire array and the filling layer. The present invention does not require an additional filter, the preparation method is simple, and is suitable for industrial production applications.

[0018] Further, in the present invention, the preparation conditions of the vertical nanowire array include: the substrate temperature is 450-480°C. The temperature of the epitaxial growth of the vertical nanowire array in the present invention is 450-480°C, which is conducive to the formation of one-dimensional nanowires, but at the same time is not conducive to the growth of two-dimensional thin film materials. Therefore, lattice defects (i.e., nanowire-substrate interface trap states) are introduced at the interface between the nanowire and the buffer layer. The present invention introduces nanowire-substrate interface trap states and utilizes the light-induced gating effect to enhance the light response in the near-infrared band, thereby achieving efficient visible blind infrared detection, and has the advantages of high stability and simple preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic cross-sectional view of a visible blind infrared photodetector based on a vertical nanowire array provided by the present invention; Figure 2 A SEM cross-sectional view of a vertical nanowire array of a visible blind infrared photodetector provided by the present invention; Figure 3 The volt-ampere characteristic curves of the visible blind infrared photoelectric detector provided by the present invention in dark state and under illumination; Figure 4 The photoluminescence spectrum of the heavily doped GaAs buffer layer of the visible blind infrared photodetector provided by the present invention; Figure 5 The light field intensity distribution from the tip of a single nanowire to the substrate in the visible blind infrared photodetector provided by the present invention; Figure 6 A spectral response diagram of the visible blind infrared photoelectric detector provided by the present invention; Figure 7 A physical image of the visible blind infrared detector provided by the present invention; In the figure: 1 is a substrate, 2 is a buffer layer, 3 is a filling layer, 4 is a vertical nanowire array, and 5 is a transparent electrode. DETAILED DESCRIPTION

[0020] The present invention provides a visible blind infrared detector, comprising a substrate; a buffer layer arranged on the upper surface of the substrate; a vertical nanowire array arranged on the upper surface of the buffer layer, and a filling layer arranged in the gaps of the vertical nanowire array; the thickness of the filling layer is the same as the height of the vertical nanowire array; and a transparent electrode arranged on the upper surfaces of the vertical nanowire array and the filling layer.

[0021] The visible blind infrared detector based on the vertical nanowire array provided by the present invention specifically refers to a visible blind infrared detector based on the vertical nanowire array, which utilizes the inherent resonant absorption effect and light-induced gating effect of the quasi-one-dimensional nanowire array to adjust the collection efficiency of photogenerated non-equilibrium carriers of different energies in the vertical nanowire channel, thereby realizing a visible blind infrared detector that does not require additional filters, has high stability and a simple preparation process, and expands its application space in monochromatic light detection and imaging systems.

[0022] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0023] The cross-sectional structure diagram of the visible blind infrared detector provided by the present invention is as follows Figure 1 As shown below, combined Figure 1 The structure of the visible blind infrared detector provided by the present invention is described in detail.

[0024] The visible blind infrared detector provided by the present invention comprises a substrate 1. In the present invention, the material of the substrate 1 is preferably gallium arsenide (GaAs).

[0025] The visible blind infrared detector provided by the present invention comprises a buffer layer 2 arranged on the upper surface of the substrate 1. In the present invention, the material of the buffer layer 2 is preferably heavily doped GaAs. The doping element of the heavily doped GaAs is Si, and the doping concentration is 10 18 cm -3 The thickness of the buffer layer 2 is preferably 5-10 nm. In the present invention, the buffer layer 2 serves as a bottom common electrode of each vertical nanowire in the vertical nanowire array 4, and is used for bottom common contact of each vertical nanowire.

[0026] The visible blind infrared detector provided by the present invention comprises a vertical nanowire array 4 arranged on the upper surface of the buffer layer 2. In the present invention, the material of the vertical nanowire array 4 preferably comprises one or more of GaAs, InP and InGaAs, and specifically GaAs in the embodiment. The height of the vertical nanowire array 4 is preferably 3-4 μm.

[0027] The visible blind infrared detector provided by the present invention includes a filling layer 3 arranged in the gap of the vertical nanowire array 4; the thickness of the filling layer 3 is the same as the height of the vertical nanowire array 4. In the present invention, the material of the filling layer 3 is preferably a thermosetting polymer, and the thermosetting polymer preferably includes photoresist and / or benzocyclobutene (BCB), specifically photoresist in the embodiment. The photoresist preferably includes AZ4620 photoresist and / or SU8 photoresist. In the present invention, the filling layer 3 is arranged in the gap with the vertical nanowire array 4, and plays a supporting role for each nanowire in the vertical nanowire array, preventing the nanowires in the vertical nanowire array 4 from falling over.

[0028] The visible blind infrared detector provided by the present invention comprises a transparent electrode 5 arranged on the upper surface of the vertical nanowire array 4 and the filling layer 3. In the present invention, the transparent electrode 5 is preferably an indium tin oxide (ITO) transparent electrode or a gallium-doped zinc oxide (GZO) transparent electrode; the thickness of the transparent electrode is 100-200 nm.

[0029] The incident light of the visible blind infrared detector provided by the present invention enters from the transparent electrode 5 of the visible blind infrared detector, and each nanowire in the vertical nanowire array 4 is preferably parallel to the incident light.

[0030] The visible blind infrared detector provided by the present invention utilizes the resonant absorption effect of the vertical nanowire array to adjust the collection efficiency of photogenerated carriers in the vertical channel of the nanowire, and by introducing nanowire-substrate interface trap states, utilizes the light-induced gating effect to enhance the light response in the near-infrared band, thereby realizing a visible blind infrared photoelectric detector with high stability and low process complexity.

[0031] The present invention provides a method for preparing the visible blind infrared detector described in the above technical solution, comprising the following steps: Preparing a buffer layer on the upper surface of the substrate; preparing a vertical nanowire array on the upper surface of the buffer layer; preparing a filling layer in the gaps of the vertical nanowire array; Transparent electrodes are prepared on the upper surfaces of the vertical nanowire array and the filling layer.

[0032] The present invention prepares a buffer layer on the upper surface of the substrate. In the present invention, the preparation method of the buffer layer is preferably a molecular beam epitaxy method. The present invention has no special requirements on the specific preparation method of the buffer layer.

[0033] After obtaining the buffer layer, the present invention prepares a vertical nanowire array on the upper surface of the buffer layer. In the present invention, the method for preparing the vertical nanowire array is preferably prepared by a molecular beam epitaxy method based on a metal autocatalytic growth method. The preparation conditions of the vertical nanowire array preferably include: the V / III ratio is preferably 15~20:1, and specifically 20:1 in the embodiment; the substrate temperature is preferably 450~480°C, and specifically 480°C in the embodiment; the growth time is preferably 1.5~2.5 hours, and specifically 2 hours in the embodiment. In a specific embodiment of the present invention, the material of the vertical nanowire array is specifically GaAs, and the V / III ratio is specifically the beam ratio of the As element in the As source and the Ga element in the Ga source used when preparing the vertical nanowire array whose material is GaAs. The substrate temperature is a substrate with a buffer layer.

[0034] After obtaining the vertical nanowire array, the present invention prepares a filling layer in the gaps of the vertical nanowire array. In the present invention, the method for preparing the filling layer preferably includes the following steps: filling the gaps of the vertical nanowire array with a thermosetting polymer, and then performing thermal curing to obtain the filling layer. The filling method of the thermosetting polymer is preferably spin coating, the rotation speed of the spin coating is preferably 1500~2000r / s, and the time is preferably 40~50s. The thermal curing is preferably carried out on a hot plate in an oven, the temperature of the thermal curing is preferably 65~70°C, and the time is preferably ≥12h; In the present invention, after the filling layer is prepared, the present invention preferably also includes: polishing the vertical nanowire array by etching or polishing to remove excess thermosetting polymer on the surface of the vertical nanowire array and expose the top of each nanowire in the vertical nanowire array.

[0035] After obtaining the vertical nanowire array and the filling layer, the present invention prepares a transparent electrode on the upper surface of the vertical nanowire array and the filling layer. In the present invention, the preparation method of the transparent electrode is preferably a dual ion beam sputtering method combined with a hard mask method. The preparation conditions of the transparent electrode preferably include: the deposition rate is preferably 5-8nm / min, specifically 8nm / min in the embodiment.

[0036] Compared with the prior art, the technical effect of the present invention is that the present invention designs a visible blind infrared photodetector based on a vertical nanowire array, effectively avoiding the high structural complexity, signal crosstalk, and other technical problems of low stability of visible blind infrared detectors based on organic semiconductor materials and the like existing in traditional coupled filter plates, and the preparation process is simple. The present invention utilizes the inherent resonant absorption effect and light-induced gating effect of a one-dimensional nanowire array to achieve spectrally selective infrared detection with high stability and low process complexity.

[0037] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0038] Example 1 This embodiment provides a visible blind infrared detector, and the cross-sectional structure diagram of the visible blind infrared detector is as follows: Figure 1 The visible blind infrared detector provided by the present invention comprises a substrate; a buffer layer arranged on the upper surface of the substrate; a vertical nanowire array arranged on the upper surface of the buffer layer, and a filling layer arranged in the gaps of the vertical nanowire array; the thickness of the filling layer is the same as the height of the vertical nanowire array; and a transparent electrode arranged on the upper surfaces of the vertical nanowire array and the filling layer.

[0039] In the visible blind infrared detector provided in this embodiment: the material of the substrate 1 is GaAs. The material of the buffer layer 2 is heavily doped GaAs (the doping element of the heavily doped GaAs is Si, and the doping concentration is 10 18 cm -3 ), the thickness of the buffer layer is 5-10 nm. The material of the vertical nanowire array 4 is GaAs. The height of the vertical nanowire array is 3-4 μm. The material of the filling layer 3 is AZ4620 photoresist, SU8 photoresist or benzocyclobutene (BCB). The transparent electrode 5 is an indium tin oxide (ITO) transparent electrode, and the thickness of the transparent electrode is 100-200 nm.

[0040] The method for preparing the visible blind infrared detector provided in this embodiment comprises the following steps: (1) Using molecular beam epitaxy technology, a heavily doped GaAs buffer layer is grown on the surface of the GaAs substrate to serve as the common contact at the bottom of the nanowire.

[0041] (2) A nanowire array was grown on the surface of the buffer layer by molecular beam epitaxy technology based on a metal autocatalytic method, with a V / III ratio of 20:1, a substrate temperature of 480°C, and a growth time of 2 hours.

[0042] (3) Spin coating the surface of the nanowire array with a thermosetting polymer AZ4260 photoresist to fill the gaps between the nanowires at a spin coating speed of 1500 rpm for 40 seconds, followed by baking in an oven for more than 12 hours at a baking temperature of 65°C to solidify the photoresist, thereby solidifying and supporting the nanowire array to prevent the nanowires from falling over.

[0043] (4) Polishing the nanowire array by etching or polishing process to remove excess thermosetting polymer on the surface and expose the top of the nanowire.

[0044] (5) A transparent indium tin oxide electrode was prepared on the surface of the nanowire array by dual ion beam sputtering technology combined with a hard mask process, with a deposition rate of 8 nm per minute.

[0045] Figure 2 The SEM cross-sectional view of the vertical nanowire array of the visible blind infrared photodetector provided in this embodiment. It can be observed that the nanowires maintain their original vertical arrangement structure, without obvious tilting or breaking within the visible range, and the height of the nanowire array is about 3-4 microns.

[0046] Figure 3The volt-ampere characteristic curves of the visible blind infrared photodetector in the dark state and under illumination provided for this embodiment. The external bias is applied to the transparent top electrode of indium tin oxide, and the GaAs substrate is kept grounded. The device has almost no obvious photocurrent response under 450 nm laser irradiation. In contrast, under 1550 nm laser irradiation, when the external bias is 5 V, the photocurrent can surge to more than 2 μA, and the device shows obvious visible blind infrared light response characteristics.

[0047] Figure 4 The photoluminescence spectrum of the heavily doped GaAs buffer layer in the visible blind infrared photodetector provided in this embodiment. The cutoff band of general gallium arsenide materials is about 870 nanometers. In contrast, the visible blind infrared photodetector prepared in the embodiment of the present invention shows high fluorescence efficiency in the infrared band at room temperature with a heavily doped GaAs buffer layer, and its fluorescence peak is significantly red-shifted compared to general gallium arsenide materials (the peak is at 1226nm). This shows that there are a large number of energy levels in the band gap of the gallium arsenide buffer layer material, and the transitions between them dominate the radiative recombination process. This phenomenon comes from the fact that a large number of crystal defects are introduced into the heavily doped GaAs buffer layer in the process of growing a vertical nanowire array on the upper surface of the buffer layer of the visible blind infrared photodetector provided by the present invention through a molecular beam epitaxy method based on a metal autocatalytic growth method.

[0048] Figure 5 The light field intensity distribution from the tip of a single nanowire to the substrate in the visible blind infrared photodetector provided in this embodiment. Among them, for visible light (such as 450 nm), light absorption and the generation of electron-hole pairs are mainly concentrated at the tip of the nanowire and do not reach the GaAs substrate. Therefore, most of the photogenerated non-equilibrium carriers undergo a long transport process (>3 μm) when transported to the bottom contact, and are easily annihilated through non-radiative recombination processes and cannot contribute to the photocurrent. In the near-infrared band (such as 1550 nm), the incident light has a longer transmission depth and can reach the gallium arsenide substrate area, and its light field mode is distributed throughout the nanowire channel. In addition, when the incident light propagates to the interface between the nanowire and the substrate, due to the sudden increase in the lateral size, the gallium arsenide substrate is distributed with dense optical modes. Therefore, compared with visible light, the generation and collection efficiency of carriers in the near-infrared region of the visible blind infrared photodetector provided in this embodiment is significantly improved.

[0049] Figure 6 Spectral response diagram of the visible blind infrared photodetector provided for this embodiment. The laser power is fixed at 700 microwatts and the wavelength range is 450 nm - 2000 nm. Obviously, the device exhibits obvious spectral selectivity, showing obvious light response in the near-infrared band, and almost no light response in the visible light band.

[0050] Figure 7 This is a real-life imaging diagram of the visible blind infrared detector based on the vertical nanowire array provided in this embodiment. Under room temperature conditions, when the external bias voltage is 5V, the device simultaneously images the visible light source (white light LED lamp) and the infrared light source (thermal coil, temperature is 1000K). It can be seen that the visible blind infrared detection device based on the vertical nanowire array provided in this embodiment only completes imaging of the infrared light source.

[0051] From the above embodiments, it can be seen that the visible blind infrared photodetector based on the vertical nanowire array provided by the present invention has a device structure from bottom to top of a substrate, a buffer layer, a filling layer, a nanowire array and a transparent electrode. The preparation steps are to first prepare a heavily doped buffer layer on the substrate as a bottom common contact by molecular beam epitaxy technology, and then further grow a vertical nanowire array and prepare a filling layer, and then use ion beam sputtering technology to prepare a transparent top electrode on the surface to form a visible blind infrared photodetector. Among them, the gaps between the nanowires are filled by spin coating a thermosetting polymer to support and fix the nanowires. The present invention utilizes the inherent resonant absorption effect and light-induced gating effect of the quasi-one-dimensional nanowire array to adjust the collection efficiency of photogenerated non-equilibrium carriers of different energies in the vertical nanowire channel, thereby realizing spectrally selective detection. The visible blind infrared photodetector has the advantages of no need for additional filters, high stability and simple preparation process.

[0052] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A visible blind infrared detector, characterized in that: It includes a substrate; a buffer layer arranged on the upper surface of the substrate; a vertical nanowire array arranged on the upper surface of the buffer layer; a filling layer arranged in the gaps of the vertical nanowire array, the thickness of the filling layer is the same as the height of the vertical nanowire array; and a transparent electrode arranged on the upper surfaces of the vertical nanowire array and the filling layer.

2. The visible blind infrared detector according to claim 1, characterized in that: The material of the vertical nanowire array includes one or more of GaAs, InP and InGaAs.

3. The visible blind infrared detector according to claim 1 or 2, characterized in that: The height of the vertical nanowire array is 3-4 μm.

4. The visible blind infrared detector according to claim 1, characterized in that: The material of the filling layer is a thermosetting polymer, and the thermosetting polymer includes photoresist and / or benzocyclobutene.

5. The visible blind infrared detector according to claim 1, characterized in that: The material of the substrate is GaAs.

6. The visible blind infrared detector according to claim 1, characterized in that: The material of the buffer layer is heavily doped GaAs; the thickness of the buffer layer is 5-10 nm.

7. The visible blind infrared detector according to claim 1, characterized in that: The transparent electrode is an indium tin oxide transparent electrode or a gallium-doped zinc oxide transparent electrode; the thickness of the transparent electrode is 100-200 nm.

8. The method for preparing a visible blind infrared detector according to any one of claims 1 to 7, characterized in that: The following steps are involved: Preparing a buffer layer on the upper surface of the substrate; preparing a vertical nanowire array on the upper surface of the buffer layer; preparing a filling layer in the gaps of the vertical nanowire array; Transparent electrodes are prepared on the upper surfaces of the vertical nanowire array and the filling layer.

9. The preparation method according to claim 8, characterized in that: The vertical nanowire array is prepared by a molecular beam epitaxy method based on a metal autocatalytic growth method; The preparation conditions of the vertical nanowire array include: V / III ratio of 15-20:1, substrate temperature of 450-480°C, and growth time of 1.5-2.5 hours.

10. The preparation method according to claim 8, characterized in that: The preparation method of the filling layer comprises the following steps: Filling the gaps of the vertical nanowire array with a thermosetting polymer, and then performing thermal curing to obtain the filling layer; the filling method of the thermosetting polymer is spin coating, the spin coating speed is 1500-2000 r / s, and the time is 40-50s; the thermal curing temperature is 65-70°C, and the time is ≥12h; The preparation method of the transparent electrode is a dual ion beam sputtering method combined with a hard mask method; the preparation conditions of the transparent electrode include: a deposition rate of 5-8 nm / min.

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