The Study Of ZnGa₂O₄ Based Solar-blind Ultraviolet Photodetectors

Recently,solar-blind ultraviolet(UV)photodetectors based on wide bandgap semiconductors have drawn widespread attention due to their extensive applications in various fields,such as missile warning,ultraviolet communication,ultraviolet monitoring,flame monitoring and so on.With the increasingly severe energy crisis,the development of self-powered solar-blind UV detectors that can work without an external power supply is also extremely important.Among many wide band gap semiconductors,ZnGa₂O₄ as a direct bandgap semiconductor has the characteristics of high electron mobility,strong radiation resistance and good thermal stability.ZnGa₂O₄has a wide bandgap of?5.0 e V,directly corresponding to the solar-blind UV detection band with wavelength less than 280 nm.Moreover,ZnGa₂O₄ with a spinel structure can control the position and ratio of Zn²⁺and Ga³⁺through the control of growth conditions,thereby realizing the control of electrical properties without doping with other elements.Therefore,ZnGa₂O₄ is a new type of ideal solar-blind ultraviolet photodetection material.However,the current research on ZnGa₂O₄ solar-blind UV photodetectors is still in its infancy,and there is no report on ZnGa₂O₄ self-powered devices.In view of this,this dissertation takes the development of ZnGa₂O₄ self-powered solar-blind UV photodetector as the main goal,focusing on the epitaxy of the ZnGa₂O₄ film,the design of the device structure,and related characteristics and mechanisms.The specific content is as follows(1)A high-quality ZnGa₂O₄ film was prepared on c-Al₂O₃ substrate using MOCVD technology,and the ZnGa₂O₄ plane asymmetric Schottky self-powered solar-blind UV photodetector was constructed.This device has excellent self-powered solar-blind UV photodetection performance.The ZnGa₂O₄ film grown on the c-Al₂O₃substrate is grown along the(111)preferred orientation,and its(222)crystal plane diffraction peak FWHM is only 0.045°,which is the narrowest value of ZnGa₂O₄ films reported so far,indicating that it has higher crystal quality.At 0 V bias,the peak responsivity of our device at 246 nm is about 22.2 m A/W with an UV-visible rejection ratio of 1.3×10⁴.More interestingly,the rise time and decay time of the device are only10 ns and 30 ns,respectively,which are much faster than that of any other previously reported self-powered solar-blind UV photodetectors to the best of our knowledge.It shows that ZnGa₂O₄ film has broad application prospects in the field of high-frequency solar-blind UV photodetection.(2)We have constructed the Si/Zn G₂O₄ self-powered solar-blind UV photodetector,and the transient peak current process of the device under 0 V was used to improve the responsivity and response speed.It also clarified that the interface pyroelectric effect of the ZnGa₂O₄ film is the main reason for the transient spike current phenomenon.The I-V curve of the device exhibits an obvious rectifying characteristic with a rectification ratio of more than 10³ at±5 V.At 0 V bias,the peak responsivity occurs at 242 nm with-3d B cut-off wavelength of?255 nm,and the UV-visible rejection ratio of our device is?3×10².More interestingly,an anomalous transient spike current phenomenon with high reproducibility can be clearly observed at 0 V bias when turning on and off 254 nm light due to interface pyroelectric effect of ZnGa₂O₄ film.The spike in transient photocurrent could efficiently improve the responsivity and the response speed of the device.Our work provides a feasible method for realizing high-performance Si/wide band gap semiconductor heterojunction self-powered solar-blind photodetectors.(3)The effect and mechanism of the SiO₂ interface layer on the photodetection performance of the Si/ZnGa₂O₄ heterojunction solar-blind ultraviolet photodetector under external bias voltage were studied in detail.It is revealed that the interface modification of the SiO₂ insertion layer and the regulation of photo-generated carriers were the main reasons for improving the performance of the device At-1 V bias,the dark current from 3.8×10^-8 to 5.7×10^-12 A.Since the insertion of the SiO₂ layer reduces the interface defect states,thereby reducing the trapping and recombination of carriers at the heterojunction interface,the rise and fall times of the device are reduced from0.96 s/0.88 s to 0.12 s/0.08 s.In addition,since Si/SiO₂ has a larger conduction band offset than Si/ZnGa₂O₄,which effectively prevents electrons generated under visible light irradiation from crossing the barrier,resulting in visible light response was suppressed and the UV-visible rejection ratio was obviously improved.This work provides a new idea for improving the performance of Si/wide band gap semiconductor heterojunction solar-blind UV photodetectors under applied bias.