Plasma enhanced photoelectric detector based on GaN / TiO2 nano array and preparation method thereof

Abstract

The invention relates to a plasma enhanced photoelectric detector based on a GaN / TiO2 nano array and a preparation method thereof, and the method comprises the steps: firstly preparing a TiO2 nano column array on an N-type Si substrate, and enabling the TiO2 nano column array to be inversely soaked in metal Ga, so as to enable the TiO2 nano column array to be covered by a Ga2O3 film; and after the quality of the Ga2O3 film is improved through oxygen annealing, the Ga2O3 film is placed in the NH3 atmosphere to be annealed, and the GaN film is obtained. And then adding silver nanoparticles, covering graphene on the particles, and finally preparing a cathode and an anode to prepare the device. According to the structure, high specific surface area and carrier transmission efficiency of the GaN / TiO2 nano array are utilized, and a plasma enhancement effect is combined, so that efficient detection of ultraviolet light and visible light is realized. The graphene covering layer enhances the plasma effect of the silver nanoparticles and provides good conductivity, and the electrodes ensure effective electron injection and hole collection to form current. The photoelectric detector has the advantages of high sensitivity, low dark current, high response speed and the like, and is suitable for ultraviolet and visible light detection application.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology, specifically relating to a plasmonic enhanced photodetector based on GaN / TiO2 nanoarrays and its fabrication method. Background Technology

[0002] With the widespread application of ultraviolet (UV) detection technology in aerospace, environmental monitoring, and other fields, wide-bandgap semiconductor materials, represented by GaN, have become crucial for constructing high-performance UV detectors. GaN-based detectors possess direct bandgap characteristics, high quantum efficiency, and solar-blindness, making them suitable for detection in high-temperature and high-radiation environments. Furthermore, their high thermal conductivity and strong chemical stability ensure long-term stable operation under harsh conditions. Some structures can even be self-driven, offering advantages such as low power consumption and miniaturization, and demonstrating great potential for integrated applications.

[0003] In terms of improving detector performance, introducing the plasmon resonance effect is an important direction. The collective oscillation of free electrons in metallic nanostructures can enhance the local electromagnetic field, and when combined with low-dimensional nanomaterials, it significantly improves sensitivity and response speed. Heterojunction structures, due to their built-in electric field, can efficiently separate photogenerated carriers and are also widely used, allowing for the control of the detection wavelength range, suppression of dark current, and improvement of signal-to-noise ratio.

[0004] However, existing technologies face numerous challenges. GaN materials suffer from high dislocation density, high cost, and integration difficulties, while their bandgap limitation hinders their performance in visible and infrared detection. Controlling interface defects in heterojunction structures remains a bottleneck for performance improvement. Plasma enhancement mechanisms are not yet mature for application in the ultraviolet band, and metal nanostructures face challenges in high loss and morphology control. TiO2 exhibits low photogenerated carrier separation efficiency in photodetectors, lacks integration strategies, and thus limits its applications. Therefore, overcoming these bottlenecks to construct a next-generation ultraviolet photodetector with high sensitivity, broad spectral response, and low power consumption is a crucial research direction. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing GaN-based photodetectors, such as the contradiction between self-driving capability and carrier transport efficiency, limited spectral response range, material defects and high cost, and low photogenerated carrier separation efficiency of TiO2 detectors. This invention provides a plasmonic-enhanced photodetector based on a GaN / TiO2 nanoarray and its fabrication method. By constructing a GaN / TiO2 heterojunction nanoarray structure and synergizing the plasmonic enhancement effect of silver nanoparticles with a graphene conductive layer, the absorption efficiency of ultraviolet-visible dual-band light, carrier separation and transport efficiency, and interface stability can be significantly enhanced, thereby achieving an integrated effect of high sensitivity, low dark current, fast response, and self-driving dual-band detection.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for fabricating a plasmonic enhanced photodetector based on a GaN / TiO2 nanoarray includes the following steps:

[0008] S1. TiO2 nanopillar arrays were prepared on an N-type Si substrate by electrochemical anodic oxidation;

[0009] S2. The TiO2 nanopillar array is inverted and immersed in liquid gallium metal to form a Ga2O3 coating layer on the surface of the TiO2 nanopillar array. Excess Ga is removed by spin coating to obtain a Ga2O3 / TiO2 nanopillar array.

[0010] S3. The Ga2O3 / TiO2 nanopillar array is subjected to oxygen annealing and ammonia annealing in sequence to transform the Ga2O3 capping layer into a GaN thin film, thereby obtaining a GaN / TiO2 nanopillar array.

[0011] S4. Spin-coat a silver nanoparticle solution onto the surface of the GaN / TiO2 nanopillar array, and heat-treat to fix the silver nanoparticles to obtain a silver nanoparticle-modified nanopillar array.

[0012] S5. A graphene layer is coated on the surface of the silver nanoparticle-modified nanopillar array.

[0013] S6. A magnetron sputtered aluminum layer is deposited on the graphene layer as the anode, and a Ti / Au layer is evaporated on the back of the N-type Si substrate as the cathode.

[0014] Furthermore, at high temperature, a graphene film is grown on a copper foil substrate by chemical vapor deposition, and the graphene film is then covered on the surface of the silver nanoparticle-modified nanopillar array to form a graphene layer.

[0015] Further, the electrochemical anodizing in step S1 specifically includes:

[0016] A titanium layer is magnetron sputtered onto the surface of the N-type Si substrate as a source for anodic titanium oxide.

[0017] Using the titanium layer as the anode and a large-area platinum sheet as the cathode, anodic oxidation is performed in a fluorine-containing electrolyte using a stepped voltage control.

[0018] Furthermore, the area of ​​the platinum sheet is ≥ twice that of the anode.

[0019] Furthermore, the conditions for the magnetron sputtered titanium layer are: vacuum degree ≤ 3~4×10 -4 Pa, sputtering power 100-200W, argon flow rate 10-30sccm, deposition thickness 400-600nm.

[0020] Furthermore, the conditions for the magnetron sputtered titanium layer are: vacuum degree ≤ 5 × 10⁻⁶. -4 Pa, sputtering power 150W, argon flow rate 20sccm, deposition thickness 500nm.

[0021] Furthermore, the fluorinated electrolyte is a mixture of glycerol and water in a volume ratio of 3:1, 0.4-0.6 wt% NH4F, and 0.01-0.2 M (NH4)2TiF6; the stepped voltage control is to first apply a voltage of 5-20V for 30s, then increase it to 30-40V and maintain it for 1-2h, and control the temperature at 25±2℃.

[0022] Furthermore, the fluorinated electrolyte is a mixture of glycerol and water in a volume ratio of 3:1, 0.5 wt% NH4F, and 0.1 M (NH4)2TiF6; the stepped voltage control involves first applying a 10V voltage for 30 seconds, then increasing it to 30-40V and maintaining it for 1-2 hours, with the temperature controlled at 25±2℃; and the voltage is monitored and adjusted in real time using a scanning electron microscope.

[0023] Furthermore, the aspect ratio of the TiO2 nanopillar array in step S1 is ≥10:1.

[0024] Furthermore, the oxygen annealing conditions in step S3 are: heating to 800°C at 50°C / min and holding at that temperature for 2 hours in an oxygen atmosphere; the ammonia annealing conditions are: heating to 1000°C at 20°C / min and holding at that temperature for 1 hour in an ammonia atmosphere.

[0025] Further, the silver nanoparticle solution in step S4 is composed of 0.01–2 mM AgNO3, ascorbic acid, and 0.01–1% PVP; the spin-coating conditions are spin-coating at 2000–4000 rpm for 30 s; and the heat treatment conditions are heating at 100–200 °C for 10 min.

[0026] Furthermore, the silver nanoparticle solution in step S4 consists of 1 mM AgNO3, ascorbic acid, and 0.5% PVP, with AgNO3 serving as the silver source, ascorbic acid as the reducing agent, and PVP as the stabilizer to prevent the aggregation of silver nanoparticles; the spin-coating conditions are spin-coating at 3000 rpm for 30 seconds; and the heat treatment conditions are heating at 150°C for 10 minutes to remove the solvent and fix the silver nanoparticles.

[0027] Furthermore, before magnetron sputtering the aluminum layer in step S6, the graphene is first subjected to oxygen plasma treatment at a power of 40-60W for 30s.

[0028] Furthermore, before magnetron sputtering the aluminum layer in step S6, the graphene is first subjected to oxygen plasma treatment at a power of 50W for 30s to remove contaminants from the graphene surface and introduce oxygen-containing functional groups to enhance metal adhesion.

[0029] Furthermore, the conditions for the magnetron sputtering of the aluminum layer in step S6 are: vacuum degree <10 -4 Pa, power 100-200W, argon flow rate 40-60sccm, substrate temperature 100-300℃, aluminum layer thickness 100-200nm; the conditions for the vapor-deposited Ti / Au layer are: vapor deposition thickness 10nm / 100nm, vapor deposition vacuum degree <10 -4 Pa.

[0030] Furthermore, the conditions for the magnetron sputtering of the aluminum layer in step S6 are: vacuum degree <10 -4 Pa, power 150W, argon flow rate 50sccm, substrate temperature 200℃, aluminum layer thickness 100~200nm; the conditions for the vapor-deposited Ti / Au layer are: vapor deposition thickness 10nm / 100nm, vapor deposition vacuum degree <10 -4 Pa.

[0031] A plasmonic-enhanced photodetector based on a GaN / TiO2 nanoarray includes:

[0032] N-type Si substrate;

[0033] TiO2 nanopillar array is located on the surface of the N-type Si substrate;

[0034] GaN thin film, covering the TiO2 nanopillar array;

[0035] Silver nanoparticles are distributed on the surface of the GaN thin film;

[0036] A graphene layer covers the silver nanoparticles;

[0037] An aluminum anode is located on the graphene layer;

[0038] The Ti / Au cathode is located on the back side of the N-type Si substrate.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] In this invention, GaN, as a key material in the photodetector, provides excellent ultraviolet light detection performance. The combination of TiO2 nanoarrays and GaN enhances the light absorption and carrier transport performance of the photodetector. This invention utilizes the semiconductor properties of GaN and TiO2, as well as the plasmonic effect of metal nanoparticles, to achieve efficient photogenerated carrier generation and transport, improving the sensitivity and response speed of the photodetector. By constructing a GaN-TiO2 heterojunction, a built-in electric field is formed, promoting the separation and transport of photogenerated carriers and reducing electron-hole recombination, thereby improving the performance of the photodetector. The introduction of metal nanoparticles enhances the optical signal and improves the detector performance. Due to the plasmonic enhancement effect, this invention also possesses a certain visible light detection capability, enabling the detection of optical signals over a wider spectral range and expanding the application scope of the photodetector. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the preparation of TiO2 nanopillar arrays in this invention;

[0042] Figure 2 This is a schematic diagram of the preparation of Ga2O3 thin films in this invention;

[0043] Figure 3 This is a schematic diagram of the structure of the photodetector of the present invention;

[0044] Figure 4 This is a graph showing the performance of ultraviolet light detection.

[0045] Figure 5 This is a test chart of visible light detection performance;

[0046] Figure 6 The graph shows the test results for photocurrent and photocurrent-to-dark-current ratio. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from publicly available commercial sources. Unless otherwise specified, all percentages mentioned in the present invention refer to mass percentage content.

[0048] This specification uses spatially relative terms such as “below,” “under,” “down,” “above,” “above,” and “upper” to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device, except for those different from those shown in the figures.

[0049] Furthermore, the use of terms such as "first" and "second" to describe various elements, layers, regions, and sections is not intended to be restrictive. The use of terms such as "having," "containing," "including," and "comprises" are open-ended terms, indicating the presence of the stated elements or features, but not excluding additional elements or features, unless the context explicitly states otherwise.

[0050] Example 1: Preparation of Nanoarrays

[0051] A schematic diagram of the fabrication of TiO2 nanopillar arrays is shown below. Figure 1 As shown.

[0052] (1) Pretreatment of N-type Si substrate

[0053] High-purity, low-defect N-type Si was selected as the substrate, which has good electrical conductivity and photoelectric properties.

[0054] The N-type Si substrate was placed in acetone, ethanol, and deionized water and ultrasonically cleaned for 15 minutes in sequence to remove organic matter and particulate contaminants attached to the surface. Then, the N-type Si substrate was immersed in a 5% hydrofluoric acid (HF) solution for 30 seconds to remove the native oxide layer on the surface. After removal, it was dried with nitrogen gas and set aside for later use.

[0055] A titanium thin film was deposited on the pretreated N-type Si substrate using magnetron sputtering, which served as the titanium source for subsequent anodizing. The sputtering parameters were set as follows: vacuum degree ≤ 5 × 10⁻⁶. -4 Pa, sputtering power 150W, argon flow rate 20sccm, deposition rate controlled at around 10nm / min, finally forming a titanium thin film with a thickness of about 500nm.

[0056] (2) Construction of an electrochemical anodic oxidation device

[0057] A glycerol:water mixture with a volume ratio of 3:1 was used as the electrolyte. 0.5 wt% ammonium fluoride (NH4F) was added as a fluorine source, and 0.1 M ammonium hexafluorotitanate [(NH4)2TiF6] was added to promote the growth of nanopillars. The pH of the electrolyte was adjusted to 4.0-5.0 using nitric acid (HNO3) or ammonia (NH3·H2O) to enhance the uniformity of charge distribution within the system.

[0058] Using the N-type Si substrate with titanium thin film deposited in step (1) as the anode and a large-area platinum sheet (platinum sheet area ≥ 2 times the anode area) as the cathode, the two electrodes are immersed in the electrolyte in parallel.

[0059] (3) Anodizing process

[0060] Anodizing is performed using a stepped voltage control mode.

[0061] In the initial stage, a low voltage of 10V is applied and maintained for 30 seconds. Then, in the main oxidation stage, the voltage is increased to 30-40V and oxidation is continued for 1-2 hours to avoid nanotube splitting or agglomeration due to high voltage.

[0062] Throughout the oxidation process, the electrolyte temperature was maintained at 25±2℃ to avoid excessively large pore sizes or structural collapse of the nanopillars due to excessive temperature. During the oxidation process, the growth status of the nanostructure was monitored in real time using a scanning electron microscope (SEM) to ensure that the aspect ratio of the nanopillars reached more than 10:1, ultimately forming a TiO2 nanopillar array.

[0063] (4) Post-processing

[0064] The anodized sample was placed in a tube furnace and heated to 450°C at a rate of 5°C / min under nitrogen protection, and held for 2 hours to convert amorphous TiO2 into anatase phase in order to enhance its photocatalytic activity.

[0065] The annealed sample was rinsed with deionized water to remove residual electrolyte and impurities from the surface, resulting in a purified TiO2 nanopillar array.

[0066] Example 2: Preparation of Ga2O3 thin films

[0067] A schematic diagram of the preparation of Ga2O3 thin films is shown below. Figure 2 As shown.

[0068] The above-mentioned N-type Si substrate with TiO2 nanopillar array was inverted and immersed in liquid gallium metal to allow the TiO2 nanopillar array to react with the liquid gallium metal, thereby generating a Ga2O3 thin film on the surface of the TiO2 nanopillar array.

[0069] After soaking, the N-type Si substrate is removed from the liquid gallium metal. At this time, the surface of the TiO2 nanopillar array is covered with a Ga2O3 film, and some unreacted liquid gallium metal remains. An appropriate amount of organic solvent acetone is added to the surface of the TiO2 nanopillar array, and the excess Ga is removed by spin coating. Finally, a TiO2 nanopillar array with a uniform Ga2O3 film on the surface is obtained.

[0070] Example 3: Preparation of GaN Thin Films

[0071] (1) Improving the quality of Ga2O3 thin films by using oxygen annealing process

[0072] The TiO2 nanopillar array covered with Ga2O3 film prepared in Example 2 was placed in a tube furnace and heated to the target temperature of 800°C at a heating rate of 50°C / min. After reaching the target temperature, it was held at this temperature for 2 hours. After annealing, the heater was turned off and the sample was allowed to cool naturally to room temperature in the tube furnace before being taken out. Throughout the process, high-purity oxygen was maintained to reduce thermal stress and preserve the crystal structure and surface morphology of the film.

[0073] (2) Preparation of GaN thin films by ammonia annealing process

[0074] The material after oxygen annealing was placed back into a tube furnace, and the furnace temperature was raised to the target temperature of 1000°C at a heating rate of 20°C / min. Ammonia (NH3) was introduced and the furnace was kept at this temperature for 1 hour. After the holding period, the heater was turned off, and the ammonia was kept in the gas supply. The sample was allowed to cool to room temperature with the furnace and then removed, thus obtaining the GaN film covering the surface of the TiO2 nanopillar array.

[0075] Example 4: Deposition of silver nanoparticles (Ag NPs)

[0076] (1) Preparation of Ag NPs solution

[0077] Silver salt solution: Prepare a 1 mM AgNO3 solution using silver nitrate (AgNO3) as the silver source;

[0078] Reducing agent: Prepare a 0.1M ascorbic acid solution using ascorbic acid (vitamin C) as the reducing agent;

[0079] Stabilizer: 0.5% polyvinylpyrrolidone (PVP) to prevent Ag NPs from agglomerating;

[0080] Ag NPs solution: Mix 1 mM AgNO3 solution, 0.1 M ascorbic acid reducing agent and 0.5% PVP stabilizer in the specified proportions.

[0081] (2) Spin coating

[0082] The GaN / TiO2 nanopillar array sample prepared in Example 3 was placed on the spin coater stage. The Ag NPs solution was slowly added dropwise to the sample surface. The spin coater was started and the sample was spin-coated at 3000 rpm for 30 seconds to allow the solution to be evenly distributed on the entire sample surface under centrifugal force.

[0083] (3) Heat treatment

[0084] The spin-coated sample was transferred to a hot plate, and the hot plate temperature was set to 150°C. After the temperature stabilized, the sample was placed flat in the center of the hot plate and heated for 10 minutes to remove the solvent in the solution and allow Ag NPs to adhere firmly to the surface of the GaN / TiO2 nanopillar array.

[0085] (4) Post-processing

[0086] After heat treatment, the sample was removed from the hot plate and allowed to cool naturally to room temperature. The sample surface was gently rinsed with deionized water to remove unfixed Ag NPs and residues; then, a nitrogen gun was used on the sample surface to obtain a GaN / TiO2 nanopillar array with Ag NPs deposited on it.

[0087] Example 5: Graphene Cover

[0088] Graphene films were grown on copper foil substrates at high temperatures using chemical vapor deposition.

[0089] The grown graphene film was transferred onto a GaN / TiO2 nanopillar array with Ag NPs deposited on it, thus covering the surface of the Ag NPs.

[0090] Example 6: Electrode Preparation

[0091] An upper electrode is deposited on graphene, and a lower electrode is deposited on an N-type Si substrate.

[0092] (1) Preparation of the anode

[0093] The graphene-coated sample prepared in Example 5 was treated with oxygen plasma at a power of 50W for 30 seconds to remove contaminants from the graphene surface and introduce oxygen-containing functional groups into the graphene surface to enhance metal adhesion.

[0094] Transfer the cleaned sample to the substrate tray of the coating equipment, start the vacuum pump, and evacuate the chamber to a vacuum level of 10. -4 Below Pa; set sputtering parameters: power 150W, argon flow rate 50sccm, substrate temperature 200℃; uniformly deposit metallic aluminum (Al) on the graphene surface to form a metal anode with a thickness of 100-200nm.

[0095] (2) Preparation of cathode

[0096] Take the sample prepared above and ultrasonically clean the back side of the N-type Si substrate with acetone and ethanol in sequence for 15 minutes; after cleaning, use a nitrogen gun to dry the surface.

[0097] Place the cleaned sample into the vapor deposition chamber, start the vacuum pump, and evacuate the chamber to a vacuum level of 10. -4Below Pa, titanium / gold (Ti / Au) is used as the vapor deposition material, and the vapor deposition is carried out by resistance heating to form a Ti / Au (10 / 100nm) ohmic contact electrode, i.e., the cathode.

[0098] Example 7: Plasma-enhanced photodetector based on GaN / TiO2 nanoarray

[0099] The plasmonic-enhanced photodetector based on GaN / TiO2 nanoarrays in this embodiment is prepared by the methods described in Examples 1-6, such as... Figure 3 As shown, it includes: an N-type Si substrate 2; a TiO2 nanopillar array 3 located on the surface of the N-type Si substrate 2; a GaN thin film 4 covering the TiO2 nanopillar array 3; silver nanoparticles 5 distributed on the surface of the GaN thin film 4; a graphene layer 6 covering the silver nanoparticles 5; an aluminum anode 7 located on the graphene layer 6; and a Ti / Au cathode 1 located on the back side of the N-type Si substrate 2.

[0100] Experimental Example 1: Ultraviolet Light Detection Performance Test

[0101] The plasmonic enhanced photodetector based on GaN / TiO2 nanoarray from Example 7 above was used to test the detection performance of 254nm ultraviolet light in self-driven mode.

[0102] Test results are as follows Figure 4 As shown, the detector's response time to 254nm ultraviolet light is 114ms, and its responsivity R is 3.74A / W. The test results demonstrate that the photodetector of this invention possesses fast response speed and high sensitivity in the ultraviolet band, meeting the core performance requirements of high-reliability ultraviolet detection scenarios such as ultraviolet early warning and ultraviolet biosensing.

[0103] Test Example 2: Visible Light Detection Performance Test

[0104] The plasmonic enhanced photodetector based on GaN / TiO2 nanoarray from Example 7 above was used to test the detection performance of 410nm visible light in self-driven mode.

[0105] Test results are as follows Figure 5 As shown, the detector's response time to 410nm visible light is 22ms, and its responsivity R is 16.04A / W. The test results demonstrate that the photodetector of this invention exhibits ultra-high-speed dynamic response characteristics and excellent photocurrent conversion efficiency in the visible light band.

[0106] Experimental Example 3: Measurement of Dark Current and Dark Current Ratio

[0107] The plasmonic-enhanced photodetector based on GaN / TiO2 nanoarray from Example 7 was used to test its electrical response performance under different illumination conditions. The current-voltage (IV) characteristic curves of the device were measured under dark conditions, 410nm visible light illumination, and 254nm ultraviolet light illumination.

[0108] Test results are as follows Figure 6 As shown, the dark current of the detector under dark conditions is about 10 pA, indicating that the device has extremely low dark-state conductivity, which effectively reduces intrinsic noise and is beneficial to improving the signal-to-noise ratio and sensitivity in weak light detection.

[0109] Regarding illumination response, when the device is illuminated by 410nm visible light, its photoluminescence-dark-current ratio (PDCR) is 3722; while under 254nm ultraviolet light illumination, its PDCR value increases to 5363. These results demonstrate that the detector of this invention exhibits significant photoelectric response under different wavelengths of illumination, especially showing higher response capability to short-wavelength ultraviolet light. This reflects its more significant signal discrimination for ultraviolet light and its superior noise resistance, further validating its application advantages in multi-band optical detection.

[0110] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for fabricating a plasmonic-enhanced photodetector based on a GaN / TiO2 nanoarray, characterized in that, Includes the following steps: S1. TiO2 nanopillar arrays were prepared on an N-type Si substrate by electrochemical anodic oxidation; S2. The TiO2 nanopillar array is inverted and immersed in liquid gallium metal to form a Ga2O3 coating layer on the surface of the TiO2 nanopillar array. Excess Ga is removed by spin coating to obtain a Ga2O3 / TiO2 nanopillar array. S3. The Ga2O3 / TiO2 nanopillar array is subjected to oxygen annealing and ammonia annealing in sequence to transform the Ga2O3 capping layer into a GaN thin film, thereby obtaining a GaN / TiO2 nanopillar array. S4. Spin-coat a silver nanoparticle solution onto the surface of the GaN / TiO2 nanopillar array, and heat-treat to fix the silver nanoparticles to obtain a silver nanoparticle-modified nanopillar array. S5. A graphene layer is coated on the surface of the silver nanoparticle-modified nanopillar array. S6. A magnetron sputtered aluminum layer is deposited on the graphene layer as the anode, and a Ti / Au layer is evaporated on the back side of the N-type Si substrate as the cathode.

2. The preparation method according to claim 1, characterized in that, The electrochemical anodizing described in step S1 specifically includes: A titanium layer is magnetron sputtered onto the surface of the N-type Si substrate as a source for anodic titanium oxide. Using the titanium layer as the anode and a large-area platinum sheet as the cathode, anodic oxidation is performed in a fluorine-containing electrolyte using a stepped voltage control.

3. The preparation method according to claim 2, characterized in that, The conditions for the magnetron sputtered titanium layer are: vacuum degree ≤ 3~4×10 -4 Pa, sputtering power 100-200W, argon flow rate 10-30sccm, deposition thickness 400-600nm.

4. The preparation method according to claim 2, characterized in that, The fluorinated electrolyte is a mixture of glycerol and water in a volume ratio of 3:1, 0.4-0.6 wt% NH4F, and 0.01-0.2 M (NH4)2TiF6; the stepped voltage control is to first apply a voltage of 5-20V for 30s, then increase it to 30-40V and maintain it for 1-2h, and control the temperature at 25±2℃.

5. The preparation method according to claim 1, characterized in that, The aspect ratio of the TiO2 nanopillar array in step S1 is ≥10:

1.

6. The preparation method according to claim 1, characterized in that, The conditions for oxygen annealing in step S3 are: heating to 800°C at 50°C / min and holding at that temperature for 2 hours in an oxygen atmosphere; the conditions for ammonia annealing are: heating to 1000°C at 20°C / min and holding at that temperature for 1 hour in an ammonia atmosphere.

7. The preparation method according to claim 1, characterized in that, The silver nanoparticle solution in step S4 consists of 0.01–2 mM AgNO3, ascorbic acid, and 0.01–1% PVP; the spin-coating conditions are spin-coating at 2000–4000 rpm for 30 s; and the heat treatment conditions are heating at 100–200 °C for 10 min.

8. The preparation method according to claim 1, characterized in that, Before magnetron sputtering the aluminum layer as described in step S6, the graphene is first subjected to oxygen plasma treatment at a power of 40-60W for 30s.

9. The preparation method according to claim 1, characterized in that, The conditions for magnetron sputtering the aluminum layer in step S6 are: vacuum degree <10 -4 Pa, power 100-200W, argon flow rate 40-60sccm, substrate temperature 100-300℃, aluminum layer thickness 100-200nm; the conditions for the vapor-deposited Ti / Au layer are: vapor deposition thickness 10nm / 100nm, vapor deposition vacuum degree <10 -4 Pa.

10. A plasmonic-enhanced photodetector based on a GaN / TiO2 nanoarray, prepared by the method of any one of claims 1-9, characterized in that, include: N-type Si substrate (2); TiO2 nanopillar array (3) is located on the surface of the N-type Si substrate (2); GaN thin film (4) covering the TiO2 nanopillar array (3); Silver nanoparticles (5) are distributed on the surface of the GaN thin film (4); A graphene layer (6) covers the silver nanoparticles (5); An aluminum anode (7) is located on the graphene layer (6); The Ti / Au cathode (1) is located on the back side of the N-type Si substrate (2).

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