Photoelectric Properties Of ZnWO₄ Thin Films Prepared By Magnetron Sputtering

Zinc tungstate(ZnWO₄)is compound with a typical formula of AWO₄.The crystal structure of ZnWO₄ is usually monoclinic,similar to the perovskite structure,belonging to wolframite type semiconductor material that can exist stably at room temperature and high temperature.Stable,unique structure,physical and chemical properties of ZnWO₄ can be used for scintillation crystals,optical fibers,photocatalysis and photoluminescence,etc.Compared with ZnWO₄,zinc tungstate film has received relatively little attention.The reasons mainly stem from the lack of efficient,high-quality,controllable and relatively low-cost methods and technologies for preparing ZnWO₄ films.In this work,ZnWO₄ film were successfully prepared by annealing the sandwich WO₃-ZnO-WO₃ heterolayer deposited by RF magnetron sputtering.At the same time,the effects of magnetron sputtering parameters,annealing temperature,time,atmosphere,etc.on the structure,morphology,luminescence and basic electrical behavior of the formed ZnWO₄ film are systematically imestigated and the key experimental parameters for the reliable preparation of the ZnWO₄ films were achieved,the photoluminescence characteristics and basic electrical behaviors of the films were tested,and finally the related mechanisms were analyzed.The main work of this paper is listed as follows:(1)ZnWO₄ thin films were achieved by annealing WO₃-ZnO-WO₃ heterolayer that were deposited on clean Si substrates by RF magnetron sputtering technique.The influences of metal Zn target,ZnO target and ZnO layer thickness on the formation of ZnWO₄ thin film and its luminescence performance during the preparation of the precursor film was investigated.A series of characterization and test results(Raman,XRD,SEM,PL)show that:the sputtering power of WO₃ layer and ZnO layer is 100 W and 80 W,and the sputtering time is 8 minutes and 5 minutes,respectively.the sputtering atmosphere is Ar:O2=5:3.ZnWO₄ polycrystalline film with preferential growth along the(100)direction can be prepared at 750°C for 30 minutes,with a grain size of 150 nm-200 nm,A round particle morphology.It can emit blue and green light under excitation at a wavelength of about 270nm.When metal Zn and ZnO targets are used,the light emission center of the film is slightly shifted,respectively,465.70 nm and 470.05 nm,respectively.And the film formed when ZnO is used as the target the luminous intensity is relatively stronger.(2)The effects of different annealing temperatures and annealing atmospheres(Air,Ar,O₂,Vacuum)on the morphology and luminescence properties of the final ZnWO₄ film were investigated.The results display that:with the increase of annealing temperature,the grain size increases significantly;under different annealing atmospheres,the luminous intensity and grain size of the film are also different.Among them,the strongest blue-green light-emitting dense film can be obtained by keeping for 30 minutes inO₂ atmosphere at 750°C.The lifetime of the PL luminescence component at 490nm of the ZnWO₄ thin film prepared by using the ZnO target material is as follows under the four annealing atmospheres are35.422?s?21.619?s?34.747?s?31.996?s respectively.Both ZnO as the target material and metal Zn as the target material annealed inO₂ atmosphere are beneficial to improve the luminescence properties of ZnWO₄ films,indicating that the luminescence performance of ZnWO₄ films can be controlled by controlling O defects in the WO₆ octahedron.(3)The basic electrical and photoelectric response properties of ZnWO₄ film were investigated.Firstly,the IV and It characteristics of the ZnWO₄ thin film prepared under air atmosphere were tested.The results show that when the test bias is 5 V,the current increase of 2.904?A and 2.392?A exists in the film under the irradiation of 365 nm and 450 nm laser,respectively.Among them,under 450 nm laser irradiation The stability of the photocurrent response is better,and the response time and recovery time are 2.01 s and 5.08s,respectively.The average effective dark resistance of ZnWO₄ films prepared under different annealing atmospheres decreases with the increase of the content of O atoms in the annealing atmosphere.After improving the electrode preparation process,the relative sensitivity of the Zn WO4 film to 365nm laser was increased to 10.35.At last,the Zn WO4film exhibits a nonlinear IV characteristic curve and the photoelectric response characteristics are varied when aluminum-doped zinc oxide(AZO)is used as the intermediate layer of the precursor film.