ZnO ultraviolet photodetector and preparation method

Abstract

The application belongs to the technical field of ultraviolet detector, and particularly relates to a ZnO ultraviolet photodetector and a preparation method thereof. The application comprises, from bottom to top, an ITO glass substrate, an n-type low-dimensional ZnO nanowire structure layer, a Mg or Cd doped ZnO thin film layer, a p-type low-dimensional ZnO nanowire structure layer and an upper electrode layer. The Mg or Cd doped ZnO thin film layer added between the p layer and the n layer can effectively widen the p-n junction depletion region, and the Mg doped ZnO not only has similar conductivity with pure ZnO but also has a continuous adjustable band gap, thereby forming a self-driven ultraviolet photodetector structure, which can effectively solve the problem of the narrow p-n junction depletion region of the existing p-n homojunction ZnO ultraviolet photodetector. Meanwhile, Ag nanoparticles are deposited on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer, so as to improve the generation of photo-generated current and the transportation of photo-generated carriers, and finally a high light responsivity ultraviolet photodetector is prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ultraviolet detector, and particularly relates to a ZnO ultraviolet photodetector and a preparation method thereof. BACKGROUND

[0002] Compared with infrared detectors, ultraviolet detectors have shorter wave bands, low false alarm rates and high detection accuracy, and thus have very important application requirements in the fields of military affairs, aviation, fire warning and environmental pollution monitoring. As a third-generation wide-bandgap semiconductor material, ZnO has a band gap of 3.37 eV. The ZnO ultraviolet photodetector is naturally filtered from the influence of visible light and infrared light, can be used without energy supply according to the photovoltaic effect, and is gradually attracting widespread attention of researchers because the preparation material is non-toxic and the raw material is abundant.

[0003] At present, the research on the ZnO ultraviolet photodetector mainly focuses on three structures of Schottky junction type, p-n heterojunction type and p-n homojunction type. The p-n homojunction ZnO ultraviolet photodetector has the characteristics of high response speed and small lattice mismatch of the interface compared with the other two types, and the p-n junction ultraviolet photodetector can form a self-driven ultraviolet photodetector device by using the photovoltaic effect, which can directly detect ultraviolet light without an external electric field and can be used without energy supply. However, because the narrow depletion region between the p-n layers greatly reduces the quantum efficiency and responsivity of the ultraviolet photodetector, the narrow depletion region of the p-n junction has always restricted the application development of the p-n homojunction ZnO ultraviolet photodetector. SUMMARY

[0004] The purpose of the application is to overcome the defect of the narrow p-n junction depletion region of the p-n homojunction ZnO ultraviolet photodetector in the prior art, and provide a ZnO ultraviolet photodetector capable of widening the depletion region and a preparation method thereof.

[0005] The technical scheme adopted by the application to solve the technical problem is: a ZnO ultraviolet photodetector, comprising, from bottom to top, an ITO glass substrate, an n-type low-dimensional ZnO nanowire structure layer, a Mg or Cd doped ZnO thin film layer, a p-type low-dimensional ZnO nanowire structure layer and an upper electrode layer.

[0006] The ITO glass substrate is further provided with a lower electrode layer; and the upper electrode layer is electrically connected with the lower electrode layer.

[0007] Further, the unit cell of the Mg or Cd doped ZnO thin film layer is Mg x Zn 16-x O 16 or Cd x Zn 16-x O16 wherein x is 0, 1, 2, 3, 4.

[0008] Further, Ag nanoparticles are deposited on the sidewall of the p-type low-dimensional ZnO nanowire structure layer.

[0009] Further, the upper electrode layer and the lower electrode layer both adopt Cr / Ni metal electrodes.

[0010] A preparation method of a ZnO ultraviolet photodetector, comprising the following steps:

[0011] S1, cleaning an ITO glass substrate; the ITO glass substrate is cleaned by ultrasonic oscillation using acetone, anhydrous ethanol and deionized water in sequence, the cleaned ITO glass substrate is blown dry by nitrogen, and the ITO glass substrate is placed on a dust-free paper;

[0012] S2, preparing a low-dimensional n-type ZnO nanowire structure layer; the n-type ZnO nanowire structure layer is prepared by a hydrothermal method;

[0013] S3, transferring the n-type ZnO nanowire structure layer obtained in step S2 to the ITO glass substrate;

[0014] S4, preparing a Mg or Cd doped ZnO thin film layer; the ITO glass substrate with the n-type ZnO nanowire structure layer is placed into a magnetron sputtering vacuum cavity, and a Mg or Cd doped ZnO thin film layer is prepared by a direct current-radio frequency co-sputtering magnetron sputtering method;

[0015] S5, the prepared Mg or Cd doped ZnO thin film layer is placed into an annealing furnace for annealing at 400-500 DEG C, the high-temperature zone is set to have a heat preservation time of 1-2 hours, and the annealing process of rapid heating and slow cooling can eliminate defects such as gaps or vacancies in the crystal grains, so that the crystal grains are rearranged to achieve a uniform and dense effect;

[0016] S6, preparing a p-type low-dimensional ZnO nanowire structure layer; the p-type low-dimensional ZnO nanowire structure layer is prepared by a hydrothermal method, and the p-type low-dimensional ZnO nanowire structure layer is arranged above the Mg or Cd doped ZnO thin film layer prepared in step S5;

[0017] S7, the product with the p-type low-dimensional ZnO nanowire structure layer prepared in step S7 is placed in a magnetron sputtering vacuum cavity, and Ag nanoparticles are deposited on the sidewall of the p-type low-dimensional ZnO nanowire structure layer by a direct current magnetron sputtering method;

[0018] S8, the upper electrode layer and the lower electrode layer are prepared on the product with the Ag nanoparticles without opening the vacuum cavity, and the preparation of the ZnO ultraviolet photodetector is completed.

[0019] Further, the process of preparing the low-dimensional n-type low-dimensional ZnO nanowire structure layer in step S2 comprises the following steps:

[0020] S21, zinc nitrate hexahydrate Zn(NO3)2·6H2O and aluminum nitrate nonahydrate Al2(NO3)3·9H2O are added to sodium hydroxide NaOH in a measuring cylinder and stirred to dissolve to obtain solution A;

[0021] S22, trisodium citrate C6H5O7Na3·2H2O is added to solution A, and after sufficient stirring, solution B is obtained;

[0022] S23, solution B is transferred to a reaction kettle, sealed, and then placed in an electric heating constant temperature drying box for hydrothermal reaction to obtain solution C;

[0023] S24, transfer to a culture dish for drying treatment to obtain an n-type low-dimensional ZnO nanowire structure layer of Al-doped ZnO.

[0024] Further, in step S4, the target material used in the direct current and radio frequency co-sputtering magnetron sputtering method is a Mg metal target and a ZnO ceramic target, and a copper metal back target is fixedly installed on the ZnO ceramic target;

[0025] The vacuum degree of the sputtering reaction cavity is 2×10 -6 -5×10 -6 Torr, the substrate temperature is 100-180℃, the working pressure is 1-2Pa, the sputtering time is 100-150 minutes, the direct current sputtering power is 70-90W, and the radio frequency sputtering power is 100-150W.

[0026] Further, in step S8, the deposition time for preparing the upper electrode layer and the lower electrode layer is 10-30 minutes, and the electrode thickness is 80-120nm.

[0027] Further, the process of preparing the low-dimensional p-type low-dimensional ZnO nanowire structure layer in step S6 comprises the following steps:

[0028] S61, zinc nitrate hexahydrate Zn(NO3)2·6H2O and aluminum nitrate nonahydrate Al2(NO3)3·9H2O are mixed and then ammonium nitrate NH4NO3 is added to obtain solution D;

[0029] S62, sodium hydroxide NaOH is added to solution D and stirred to dissolve in a measuring cylinder to obtain solution E;

[0030] S63, trisodium citrate C6H5O7Na3·2H2O is added to the above-mentioned solution E and fully dissolved to obtain solution F;

[0031] S64, after moving solution F to the reaction kettle and sealing, the hydrothermal reaction is carried out in an electric heating constant temperature drying box to obtain solution G after reaction;

[0032] S65, solution G obtained in step S64 is transferred to a culture dish for drying treatment to obtain the p-type low-dimensional ZnO nanowire structure layer of Al-N co-doped ZnO.

[0033] Further, in step S7, the Ag nanoparticles are prepared by direct current magnetron sputtering, a 99.99% pure Ag metal target is used, the vacuum degree of the reaction cavity is set to 2*10 -6 - 5*10 -6 Torr, the substrate temperature is 100-180 DEG C, the working pressure is 1-2 Pa, the sputtering time is 2-5 minutes, and the power of the direct current sputtering is 70-90 W.

[0034] The p-type low-dimensional ZnO nanowire structure layer / Mg or Cd doped ZnO thin film layer / n-type low-dimensional ZnO nanowire structure layer ultraviolet photodetector structure of the application has the advantages that:

[0035] 1. The Mg or Cd doped ZnO thin film layer between the p layer and the n layer can effectively widen the p-n junction depletion region, the Mg doped ZnO has similar conductivity with pure ZnO and a continuous adjustable band gap, and the self-driven p-type low-dimensional ZnO nanowire structure layer / Mg or Cd doped ZnO thin film layer / n-type low-dimensional ZnO nanowire structure layer ultraviolet photodetector structure can effectively solve the problem of narrow p-n junction depletion region of the existing p-n homojunction ZnO ultraviolet photodetector, the Ag nanoparticles on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer can further improve light absorption by using surface plasmon enhancement, thereby improving the generation of photo-generated current and the transport of photo-generated carriers, and finally preparing the ultraviolet photodetector with high light responsivity.

[0036] 2. The Mg or Cd doping does not change the conduction form of the ZnO layer, only changes the band gap, and the n-type low-dimensional ZnO nanowire structure layer / Mg or Cd doped ZnO thin film layer / p-type low-dimensional ZnO nanowire structure layer structure not only makes the optical response further deviate to the ultraviolet light, but also controls the optical response peak by controlling the Mg doping amount, and the widening of the depletion region reduces the junction capacitance, so that the quantum efficiency and responsivity of the ultraviolet photodetector are greatly improved.

[0037] 3、The application adopts p-type low-dimensional nano-structure ZnO and n-type low-dimensional nano-structure ZnO, so that the ZnO ultraviolet photodetector has a larger specific surface area, thereby making the ZnO ultraviolet photodetector have better photoconductivity and easily form an efficient low-dimensional conductive channel. Meanwhile, the ZnO ultraviolet photodetector of the application is surface passivated by depositing Ag nanoparticles on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer to reduce surface trapped charges. The Ag nanoparticles are deposited on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer, which on one hand solves the problem of surface trapped charges due to surface passivation, and on the other hand makes the light absorption enhanced and produces localized surface plasmon resonance, so that the surface is modified by depositing metal particles on the surface of the low-dimensional structure, and the ZnO ultraviolet photodetector has significantly increased light absorption, thereby improving the detection performance and efficiency of the ZnO ultraviolet photodetector.

[0038] 4、The ultraviolet detector of the application adopts Cr / Ni metal electrodes, so that the ultraviolet detector has higher ohmic contact and lower resistance value. BRIEF DESCRIPTION OF DRAWINGS

[0039] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0040] Figure 1 Fig. 1 is a structure schematic diagram of the ZnO ultraviolet photodetector of the embodiment of the application;

[0041] Figure 2 Fig. 2 is a pure ZnO energy band structure diagram;

[0042] Figure 3 Fig. 3 is a curve diagram of the change of the band gap value with the Mg doping amount when Mg is doped into ZnO;

[0043] Figure 4 Fig. 4 is a curve diagram of the change of the band gap value with the Mg doping amount when Mg is diffused into the n-type low-dimensional ZnO nanowire structure layer;

[0044] Figure 5 Fig. 5 is an energy band structure diagram of the Mg diffused into the p-type low-dimensional ZnO nanowire structure layer;

[0045] Figure 6 Fig. 6 is a light absorption rate curve diagram of the Mg diffused into the p-type low-dimensional ZnO nanowire structure layer;

[0046] Figure 7 Fig. 7 is a SEM surface morphology diagram of the Mg or Cd doped ZnO thin film layer prepared by the magnetron sputtering method;

[0047] Figure 8 Fig. 8 is an I-V curve of different contact electrodes;

[0048] Figure 9is a preparation method flow chart of the ZnO ultraviolet photodetector.

[0049] In the figure: 1, ITO glass substrate, 2, lower electrode layer, 3, n-type low-dimensional ZnO nanowire structure layer, 4, Mg or Cd doped ZnO thin film layer, 5, p-type low-dimensional ZnO nanowire structure layer, 6, Ag nanoparticles, 7, upper electrode layer. DETAILED DESCRIPTION

[0050] The application will now be described in further detail with reference to the drawings. These drawings are simplified schematic diagrams which only show the basic structure of the application in a schematic manner, and thus only show the components relevant to the application.

[0051] As Figures 1-8 shown in the specific embodiment of the ZnO ultraviolet photodetector with the Mg or Cd doped ZnO thin film layer 4 as the intermediate layer, the ITO glass substrate 1, the n-type low-dimensional ZnO nanowire structure layer 3, the Mg or Cd doped ZnO thin film layer 4, the p-type low-dimensional ZnO nanowire structure layer 5 and the upper electrode layer 7 are sequentially arranged from bottom to top; the lower electrode layer 2 is further arranged on the ITO glass substrate 1; the upper electrode layer 7 is electrically connected with the lower electrode layer 2. It needs to be further explained that the unit cell of the Mg or Cd doped ZnO thin film layer 4 in step S4 is Mg x Zn 16-x O 16 or Cd x Zn 16-x O 16 , wherein x is 0, 1, 2, 3, 4, the number of doped Mg or Cd atoms in the Mg or Cd doped ZnO thin film layer 4 is determined by replacing the Zn site with Mg or Cd in the Zn 16 O 16 atomic unit cell model established in the Material Studio software.

[0052] The calculation method of the doping ratio of Mg in the Mg or Cd doped ZnO thin film layer 4 is as follows: the Zn 16 O 16 atomic unit cell model is established in the Material Studio software, the Zn site is replaced with Mg or Cd, and the number of Mg or Cd atoms is set to x, at this time the unit cell is Mg x Zn 16-x O 16 , the energy band structure of the unit cell when x = 0, 1, 2, 3, 4 is calculated respectively by using the first principle method based on the density functional theory, and the energy band structure diagram is drawn, wherein EF is the Fermi level position, CBM is the conduction band minimum, VBM is the valence band maximum, and the band gap value = CBM-VBM.

[0053] Figure 2For the band structure diagram when x=0, it can be seen that there is a blank area along the ordinate, which is the band gap of the band, the area above the CBM is the conduction band, and the area below the VBM is the valence band; the band gap value of the Mg or Cd doped ZnO thin film layer 4 after Mg or Cd is doped into ZnO is calculated, and a change curve is drawn, as shown in Figure 3 Taking Mg as an example, as shown in the figure, with the increase of the doping amount of Mg, the band gap value of the structure increases; further, the diffusion effect of Mg doped into the intermediate layer to the n-type low-dimensional ZnO nanowire structure layer 3 and the p-type low-dimensional ZnO nanowire structure layer 5 is calculated: for the n-type low-dimensional ZnO nanowire structure layer 3, as the doping amount of Mg increases, the band gap value also presents an increasing trend, as shown in Figure 4 ; for the p-type low-dimensional ZnO nanowire structure layer 5, it can be seen from the band diagram that due to the doping of Mg, the impurity level position is lowered, and the impurities are more easily ionized, which increases the conductivity of the p-type low-dimensional ZnO nanowire structure layer 5, as shown in Figure 5 ; the optical absorption characteristics of the structure are calculated by the formula It can be seen that the doping of Mg increases the light absorption of the p-type low-dimensional ZnO nanowire structure layer 5 in the ultraviolet and visible light regions, which is beneficial to the light absorption and light response of the overall structure of the ultraviolet detector, and specific reference is made to Figure 6 Compared with the bulk structure, the one-dimensional structure such as nanorod and nanowire and the zero-dimensional structure such as nanosheet are collectively referred to as low-dimensional structure, and the low-dimensional structure has a larger specific surface area, which can effectively increase the light absorption.

[0054] The first principle calculation method based on the density functional theory is adopted to calculate the change of the band gap of the Mg doped ZnO thin film layer 4 with the Mg doping amount, and taking Mg as an example, it can be seen from Figure 3 that the band gap increases with the increase of the Mg doping amount, and the ultraviolet excitation peak moves to the low wavelength direction, and the position of the ultraviolet emission peak can be controlled by adjusting the Mg doping amount; at the same time, the diffusion of Mg element to the n-type low-dimensional ZnO nanowire structure layer 3 and the p-type low-dimensional ZnO nanowire structure layer 5 is discussed in a calculated way, it can be found that with the increase of the Mg doping amount, the band gap value of the n-type low-dimensional ZnO nanowire structure layer 3 presents a gradually increasing trend, and the depth of the impurity level of the n-type low-dimensional ZnO nanowire structure layer 3 is first deepened and then shallowed, that is, the excitation ability of the electron is first weakened and then strengthened, when the number of Mg doping atoms x is 4, the distance between the impurity level and the conduction band bottom is smaller than that when Mg is not doped, which indicates that the conductivity is better at this time; for the p-type low-dimensional ZnO nanowire structure layer 5, it can be seen from the band diagram that due to the doping of Mg, the impurity level position is lowered, and the impurities are more easily ionized, which increases the conductivity of the p-type low-dimensional ZnO nanowire structure layer 5, further, the optical absorption characteristics of the structure are calculated by the formula The optical absorption characteristics of the structure are calculated, and the incorporation of Mg increases the light absorption of the p-type low-dimensional ZnO nanowire structure layer 5 in the ultraviolet and visible light regions. The ZnO ultraviolet photodetector with a Mg or Cd doped ZnO thin film layer 4 as an intermediate layer has strong light absorption and light response.

[0055] The sidewall of the p-type low-dimensional ZnO nanowire structure layer 5 is deposited with Ag nanoparticles 6. The low-dimensional structure ZnO ultraviolet photodetector has better photoconductivity due to a larger specific surface area, i.e., the ratio of surface area to volume, and is easy to form an efficient low-dimensional conductive channel. The n-type low-dimensional ZnO nanowire structure layer 3 and the p-type low-dimensional ZnO nanowire structure layer 5 adopt a low-dimensional nanowire structure, which has great value for improving the overall light response performance. However, the low-dimensional structure also has the problem of surface trapping of charges, which leads to an increase in the dark current of the ultraviolet photodetector and a prolongation of the response time. Based on this problem, the present application considers depositing Ag nanoparticles 6 on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer 5 to perform surface passivation to reduce surface trapping of charges. Since the surface plasmon polariton SPP wave resonance peak of the Ag nanoparticles 6 in the high-order vibration mode is located near 380 nm, it is well matched with the response waveband of ZnO. Therefore, Ag nanoparticles 6 are more suitable metal nanoparticles for ZnO-based ultraviolet photodetectors. The deposition of Ag nanoparticles 6 on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer 5 not only solves the problem of surface trapping of charges due to surface passivation, but also enhances light absorption and produces localized surface plasmon resonance LSPR due to metal particles. Therefore, depositing metal particles on the surface of the low-dimensional structure not only can achieve surface modification, but also can increase light absorption, and has a more significant effect.

[0056] It should be noted that the ZnO in the ZnO ultraviolet photodetector in the present embodiment can also be replaced by other wide-bandgap semiconductor materials such as SnO2, etc. in a homojunction structure. In the present embodiment, only ZnO is taken as an example.

[0057] The ultraviolet detector of the present application adopts Cr / Ni metal electrode, so that the ultraviolet detector has higher ohmic contact and lower resistance value. In the present application, through a large number of experiments, the contact electrode of the ultraviolet detector structure is compared and studied, and a direct current / radio frequency magnetron sputtering mode is adopted, the target material is selected from 99.99% pure φ50mm*5mm Ag, Cr, Ti, Al, Ni metal target material, and 99.99% pure φ50mm*3mm ZnO ceramic target, wherein a φ50mm*2mm copper metal back target is fixed on the ZnO ceramic target, the power of direct current sputtering is 80W, the power of radio frequency sputtering is 120W, the sputtering time is 5 minutes, AZO / Ag / AZO, Cr / Ni, AZO / Ti / AZO, Cr, Ti / Ag, Al / Ag electrodes are prepared as front electrodes respectively, and I-V curves are tested, it can be seen that the resistance value of AZO / Cr / AZO electrode is the smallest, and the resistance values of AZO / Ag / AZO, Cr / Ni, AZO / Ti / AZO, Cr, Ti / Ag, Al / Ag contact electrodes increase in turn, for the ultraviolet detector of the present application, the adoption of Cr / Ni electrode makes the ultraviolet detector have higher ohmic contact and lower resistance value.

[0058] As shown in Figure 9 A preparation method of a ZnO ultraviolet photodetector with a Mg or Cd doped ZnO thin film layer 4 as an intermediate layer, comprising the following steps:

[0059] S1, cleaning the ITO glass substrate 1; the ITO glass substrate 1 is ultrasonically cleaned with acetone, anhydrous ethanol and deionized water in sequence, the cleaned ITO glass substrate 1 is blown dry with nitrogen, and the ITO glass substrate 1 is placed on a dust-free paper.

[0060] S2, preparing a low-dimensional n-type low-dimensional ZnO nanowire structure layer 3, the n-type low-dimensional ZnO nanowire structure layer 3 is prepared by a hydrothermal method.

[0061] S3, transferring the n-type low-dimensional ZnO nanowire structure layer 3 obtained in step S2 to the ITO glass substrate 1.

[0062] S4, preparing a Mg or Cd doped ZnO thin film layer 4, the ITO glass substrate 1 with the n-type low-dimensional ZnO nanowire structure layer 3 is placed in a magnetron sputtering vacuum cavity, and a Mg or Cd doped ZnO thin film layer 4 is prepared by a direct current-radio frequency co-sputtering magnetron sputtering mode.

[0063] S5, the prepared Mg or Cd doped ZnO thin film layer 4 crystal grains are placed in an annealing furnace for annealing at 400-500℃, and the high temperature zone is set to have a heat preservation time of 1-2 hours, so that the crystal grains are rearranged. It should be noted that in this embodiment, the annealing is performed at 450℃, the high temperature zone is set to have a heat preservation time of 1 hour, and the annealing process of rapid heating and slow cooling can eliminate defects such as gaps or vacancies in the crystal grains, so that the crystal grains are rearranged, and a uniform and dense effect is achieved.

[0064] S6, a p-type low-dimensional ZnO nanowire structure layer 5 is prepared; the p-type low-dimensional ZnO nanowire structure layer 5 is prepared by using a hydrothermal method, and the p-type low-dimensional ZnO nanowire structure layer 5 is arranged above the Mg or Cd doped ZnO thin film layer 4 prepared in step S5.

[0065] S7, the product with the p-type low-dimensional ZnO nanowire structure layer 5 prepared in step S7 is placed in a magnetron sputtering vacuum cavity, and Ag nanoparticles 6 are deposited on the side wall of the p-type low-dimensional ZnO nanowire structure layer 5 by using a direct current magnetron sputtering method.

[0066] The Ag nanoparticles 6 in step S7 are prepared by using a direct current magnetron sputtering method, an Ag metal target with a purity of 99.99% is used, the vacuum degree of the reaction cavity is set to 2x10 -6 -5x10 -6 Torr, the substrate temperature is 100-180℃, the working pressure is 1-2 Pa, the sputtering time is 2-5 minutes, and the power of the direct current sputtering is 70-90 W.

[0067] S8, the upper electrode layer 7 and the lower electrode layer 2 are prepared on the product with the Ag nanoparticles 6 without opening the vacuum cavity, and the preparation of the ZnO ultraviolet photodetector with the Mg or Cd doped ZnO thin film layer 4 as the intermediate layer is completed.

[0068] In step S2, the preparation process of the low-dimensional n-type low-dimensional ZnO nanowire structure layer 3 includes the following steps:

[0069] S21, zinc nitrate hexahydrate Zn(NO3)2·6H2O and aluminum nitrate nonahydrate Al2(NO3)3·9H2O are added to a measuring cylinder containing sodium hydroxide NaOH, stirred and dissolved to obtain solution A.

[0070] S22, trisodium citrate C6H5O7Na3·2H2O is added to solution A, and solution B is obtained after sufficient stirring.

[0071] S23, solution B is transferred to a reaction kettle, sealed, and then placed in an electric heating constant temperature drying box for hydrothermal reaction to obtain solution C.

[0072] S24, transfer to the culture dish drying treatment to obtain Al-doped ZnO n-type low-dimensional ZnO nanowire structure layer 3.

[0073] It needs to be further explained that the Mg-doped ZnO film in the above step S4 is prepared by a direct current and radio frequency co-sputtering magnetron sputtering method, including the following steps:

[0074] S41, clean the ITO glass substrate 1; ultrasonic oscillation cleaning is sequentially performed using acetone, anhydrous ethanol, and deionized water, nitrogen is used for drying, and the substrate is placed on a dust-free paper for standby.

[0075] S42, a target material is a φ50mm×5mm Mg metal target with a purity of 99.99%, and a φ50mm×3mm ZnO ceramic target with a purity of 99.99%, a φ50mm×2mm copper metal back target is fixedly installed on the ZnO ceramic target, and in the process of direct current and radio frequency co-sputtering magnetron sputtering preparation, the sputtering conditions are as follows: the sputtering reaction cavity vacuum degree is 2×10 -6 -5×10 -6 Torr, the substrate temperature is 100-180℃, the working pressure is 1-2Pa, the sputtering time is 100-150 minutes, the direct current sputtering power is 70-90W, and the radio frequency sputtering power is 100-150W.

[0076] In this embodiment, the optimal sputtering conditions are adopted, the sputtering reaction cavity vacuum degree is set to 2×10-6 Torr, the substrate temperature is 150℃, the working pressure is 1.5Pa, the sputtering time is 120 minutes, the direct current sputtering power is 80W, and the radio frequency sputtering power is 120W.

[0077] S43, the prepared sample is placed in an annealing furnace for annealing at 450℃, the high-temperature zone is set to keep warm for one hour, so that the crystal grains are rearranged, and the generation of defects such as vacancies and dislocations is reduced.

[0078] S44, the sample is tested, the crystal lattice structure is tested by XRD, the surface morphology is observed by scanning electron microscopy, the electrical properties are measured by a Hall tester, the optical properties are measured by a UV-visible light spectrophotometer, and the sample surface morphology is as shown in Figure 7 The SEM surface morphology is relatively uniform, that is, it meets the production requirements, and can be applied to the Mg or Cd-doped ZnO film layer 4 as an intermediate layer of a ZnO ultraviolet photodetector.

[0079] In this embodiment, the Mg or Cd-doped ZnO film layer 4 is prepared by a direct current-radio frequency co-sputtering magnetron sputtering method, and the performance is tested and characterized, so that the crystal grains in the Mg or Cd-doped ZnO film layer 4 are uniformly distributed, and the purpose of widening the p-n junction depletion region of the p-n homojunction ZnO ultraviolet photodetector is achieved.

[0080] The process of preparing the low-dimensional p-type low-dimensional ZnO nanowire structure layer 5 in step S6 includes the following steps:

[0081] S61, after mixing zinc nitrate hexahydrate Zn(NO3)2·6H2O and aluminum nitrate nonahydrate Al2(NO3)3·9H2O, add ammonium nitrate NH4NO3 as a p-type reagent to obtain solution D.

[0082] S62, add sodium hydroxide NaOH to solution D, stir and dissolve in a measuring cylinder to obtain solution E.

[0083] S63, add trisodium citrate C6H5O7Na3·2H2O to the above-mentioned solution E, fully dissolve to obtain solution F.

[0084] S64, move solution F to a reaction kettle, seal it, and then put it into an electric heating constant temperature drying box to perform hydrothermal reaction to obtain reacted solution G.

[0085] S65, transfer solution G obtained in step S64 to a culture dish and dry to obtain an Al-N co-doped ZnO p-type low-dimensional ZnO nanowire structure layer 5.

[0086] In step S8, without opening the vacuum chamber, continue to use the method of direct current magnetron sputtering to prepare the upper electrode layer 7 and the lower electrode layer 2, the deposition time is 10-30 minutes, φ50mm×5mm Cr and Ni metal targets with a purity of 99.99% are used, and the preparation parameters are as follows: the reaction cavity vacuum degree is set to 2×10 -6 Torr, the substrate temperature is 150℃, the working pressure is 1.5Pa, the sputtering time is 20 minutes, the direct current sputtering power is 80W, then put it into an annealing furnace in vacuum to anneal at 450℃, set the high temperature zone to keep warm for one hour, obtain the Cr / Ni thin film upper electrode layer 7 and lower electrode layer 2, and the electrode thickness is 80-120nm, and the best thickness is 100nm.

[0087] It needs to be further explained that the application adopts p-type low-dimensional nano-structure ZnO and n-type low-dimensional nano-structure ZnO, so that the ZnO ultraviolet photodetector has a larger specific surface area, thereby making the ZnO ultraviolet photodetector have better photoconductivity and easily form a high-efficiency low-dimensional conductive channel. Meanwhile, the ZnO ultraviolet photodetector of the application performs surface passivation by depositing Ag nanoparticles 6 on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer 5 to reduce surface trapped charges. The Ag nanoparticles 6 are deposited on the surface of the low-dimensional p-type low-dimensional ZnO nanowire structure layer 5, which on one hand solves the problem of surface trapped charges due to surface passivation, and on the other hand makes the light absorption enhanced and produces localized surface plasmon resonance, so that the surface modification is realized by depositing metal particles on the surface of the low-dimensional structure, and at the same time the ZnO ultraviolet photodetector has a significantly increased light absorption, thereby improving the detection performance and efficiency of the ZnO ultraviolet photodetector. The Mg or Cd doped ZnO thin film layer 4 thin film is prepared by the direct-current-radio frequency co-sputtering magnetron sputtering experiment method in the embodiment of the application, so as to ensure that the crystal grains on the Mg or Cd doped ZnO thin film layer 4 thin film are uniformly distributed.

[0088] It should be understood that the specific embodiments described above are only used to explain the application, and are not used to limit the application. The obvious changes or modifications derived from the spirit of the application are still within the protection scope of the application.

Claims

1. A method for preparing a ZnO ultraviolet photodetector, characterized in that, The method comprises the following steps: S1, cleaning the ITO glass substrate (1); the ITO glass substrate (1) is cleaned by ultrasonic oscillation using acetone, anhydrous ethanol and deionized water in sequence, the cleaned ITO glass substrate (1) is dried by nitrogen, and the ITO glass substrate (1) is placed on a dust-free paper; S2, preparing a low-dimensional n-type low-dimensional ZnO nanowire structure layer (3); the n-type low-dimensional ZnO nanowire structure layer (3) is prepared by a hydrothermal method; S3, transferring the n-type low-dimensional ZnO nanowire structure layer (3) obtained in step S2 to the ITO glass substrate (1); S4, preparing a Mg or Cd doped ZnO thin film layer (4); placing the ITO glass substrate (1) with the n-type low-dimensional ZnO nanowire structure layer (3) into a magnetron sputtering vacuum cavity, and preparing a Mg or Cd doped ZnO thin film layer (4) by using a direct current-radio frequency co-sputtering magnetron sputtering method; a unit cell of the Mg or Cd doped ZnO thin film layer (4) is Mg x Zn 16-x O 16 or Cd x Zn 16-x O 16 , wherein x is 0, 1, 2, 3, 4. S5, annealing the prepared Mg or Cd doped ZnO thin film layer (4) crystal grain in an annealing furnace at 400-500 DEG C, and setting the high-temperature zone to be heat preserved for 1-2 hours; S6, preparing a low-dimensional p-type low-dimensional ZnO nanowire structure layer (5); the low-dimensional p-type low-dimensional ZnO nanowire structure layer (5) is prepared by a hydrothermal method, and the low-dimensional p-type low-dimensional ZnO nanowire structure layer (5) is arranged above the Mg or Cd doped ZnO thin film layer (4) prepared in step S5; S7, placing the product with the prepared low-dimensional p-type low-dimensional ZnO nanowire structure layer (5) in a magnetic control sputtering vacuum cavity, and depositing Ag nanoparticles (6) on the sidewall of the low-dimensional p-type low-dimensional ZnO nanowire structure layer (5) by a direct current magnetic control sputtering method; S8, preparing an upper electrode layer (7) and a lower electrode layer (2) on the product with the Ag nanoparticles (6) without opening the vacuum cavity, and completing the preparation of the ZnO ultraviolet photodetector with the Mg or Cd doped ZnO thin film layer (4) as an intermediate layer.

2. The method of claim 1, wherein the ZnO UV photodetector is prepared by the steps of: (a) preparing a ZnO film on a substrate; (b) depositing a metal layer on the ZnO film; and (c) depositing a transparent conductive layer on the metal layer. The preparation process of the low-dimensional n-type low-dimensional ZnO nanowire structure layer (3) in step S2 comprises the following steps: S21, adding zinc nitrate hexahydrate Zn (NO3) 2·6H2O and aluminum nitrate nonahydrate Al2 (NO3) 3·9H2O solutes into sodium hydroxide NaOH in a measuring cylinder to be stirred and dissolved to obtain solution A; S22, adding trisodium citrate C6H5O7Na3·2H2O into solution A, fully stirring and then obtaining solution B; S23, transferring solution B into a reaction kettle, sealing, placing into an electric heating constant temperature drying box to perform a hydrothermal reaction, and obtaining solution C; S24, transferring into a culture dish to perform drying treatment, and obtaining an Al doped ZnO n-type low-dimensional ZnO nanowire structure layer (3).

3. The method of claim 1, wherein the ZnO UV photodetector is prepared by the following steps: (a) depositing a ZnO film on a substrate; (b) depositing a metal film on the ZnO film; and (c) depositing a passivation layer on the metal film. In step S4, the target material used in the direct current and radio frequency co-sputtering magnetic control sputtering method is a Mg metal target and a ZnO ceramic target, and a copper metal back target is fixedly installed on the ZnO ceramic target; The sputtering reaction cavity vacuum is 2x10 -6 -5x10 -6 -3 Torr, the substrate temperature is 100-180℃, the working pressure is 1-2 Pa, the sputtering time is 100-150 minutes, the direct current sputtering power is 70-90 W, and the radio frequency sputtering power is 100-150 W.

4. The method for fabricating a ZnO ultraviolet photodetector according to claim 1, characterized in that: In step S8, the deposition time for preparing the upper electrode layer (7) and the lower electrode layer (2) is 10-30 minutes, and the electrode thickness is 80-120 nm.

5. The method for fabricating a ZnO ultraviolet photodetector according to claim 1, characterized in that, The preparation process of the low-dimensional p-type low-dimensional ZnO nanowire structure layer (5) in step S6 comprises the following steps: S61, mixing zinc nitrate hexahydrate Zn (NO3) 2·6H2O and aluminum nitrate nonahydrate Al2 (NO3) 3·9H2O solutes, and then adding ammonium nitrate NH4NO3 to obtain solution D; S62, adding sodium hydroxide NaOH into solution D to be stirred and dissolved in a measuring cylinder to obtain solution E; S63, adding trisodium citrate C6H5O7Na3·2H2O into the above solution E to obtain solution F after fully dissolving; S64, moving the solution F to a reaction kettle, sealing and then putting into an electric heating constant temperature drying box to perform hydrothermal reaction to obtain a reacted solution G; S65, transferring the solution G obtained in step S64 to a culture dish to perform drying treatment to obtain an Al-N co-doped ZnO p-type low-dimensional ZnO nanowire structure layer (5).

6. The method of claim 1, wherein the ZnO UV photodetector is prepared by the steps of: The Ag nanoparticles (6) in step S7 are prepared by direct current magnetron sputtering, using a Ag metal target with a purity of 99.99%, a reaction cavity vacuum degree of 2×10 -6 to 5×10 -6 Torr, a substrate temperature of 100-180°C, a working pressure of 1-2 Pa, a sputtering time of 2-5 minutes, and a direct current sputtering power of 70-90 W.

7. A ZnO UV photodetector, characterized in that: The preparation method of the ZnO ultraviolet photodetector is prepared by the method in any one of claims 1-6, comprising ITO glass substrate (1), n-type low-dimensional ZnO nanowire structure layer (3), Mg or Cd doped ZnO thin film layer (4), p-type low-dimensional ZnO nanowire structure layer (5) and upper electrode layer (7) arranged in turn from bottom to top; The ITO glass substrate (1) is further provided with a lower electrode layer (2); the upper electrode layer (7) is electrically connected with the lower electrode layer (2). 8.The ZnO UV photodetector according to claim 7, wherein: The upper electrode layer (7) and the lower electrode layer (2) are both Cr / Ni metal electrodes.

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