Study On Modulating The Physical Properties Of ZnGa₂O₄ Thin Film And Its Ultraviolet Detector Device

Due to its intrinsic advantages of low background noise,high signal-to-noise ratio,high sensitivity and strong anti-jamming capability,solar-blind ultraviolet photodetectors（UV PDs）have demonstrated its important application value in military and civil fields such as optical communication,missile early warning,biomedicine,tail-flame detection,and environmental detection.In recent years,solar-blind UV PDs have been proposed as a"5S"standard:high sensitivity,high signal-to-noise ratio,high spectral selectivity,high response speed and high stability.Therefore,solar-blind UV PDs based on wide-band semiconductors have also received more and more attention.The spinel structured ZnGa₂O₄ material is a new type of direct bandgap oxide semiconductor with an optical bandgap of～4.9 e V,which directly corresponds to the solar-blind UV wavelength band（200 nm-280 nm）,and at the same time possesses a strong resistance to irradiation and an excellent thermal stability,making it a natural candidate for solar-blind UV photodetection.In addition,thanks to the unique crystal structure of the material(double cation Zn²⁺and Ga³⁺),the electrical properties can be regulated without additional doping,which provides more possibilities for the development of solar-blind UV PDs to meet the"5S"standard.People also pay attention to the excellent performance and potential technical value of spinel oxide ZnGa₂O₄.However,compared with the current research hotspotβ-Ga₂O₃,its research is still very little.Based on ZnGa₂O₄ solar-blind UV PD device research has just begun.In terms of device structure,it mainly focuses on photoconductor devices and Schottky junction photodiodes,and there is no report on ZnGa₂O₄-based p-n junction photodiodes.Therefore,this dissertation takes the spinel structure ultra-wideband semiconductor ZnGa₂O₄ as the absorbing material of solar-blind UV rays,and takes the p-n junction photodiode UV PD as the development target,and carries out the optimization of ZnGa₂O₄ thin film growth process parameters and post-processing process,the exploration of the p-n structure construction scheme of spinel oxide ultra-wideband semiconductor,and the evaluation of the photoelectric response characteristics of the spinel oxide p-n junction photodiode.The research work of spinel oxide ZnGa₂O₄ in the development of solar-blind UV PD has shown its technical value,and the main research work and the research results are as follows:（1）ZnGa₂O₄ thin films were deposited on c-plane sapphire substrate by RF magnetron sputtering.Firstly,the effects of different substrate temperatures on the ZnGa₂O₄ films and their photoelectric properties were investigated,and the comparison revealed that the ZnGa₂O₄ films grown at the substrate temperature of 700℃had the best quality and their photoconductivity properties were optimal.Secondly,the effect of oxygen flux on the microstructure of ZnGa₂O₄ films and their photoconductivity properties was verified,and it was found that the ZnGa₂O₄ films grown under oxygen-containing atmosphere had better crystallization quality and lower oxygen vacancy concentration.On this basis,a ZnGa₂O₄/Au Schottky junction photodiode was developed,and the Schottky junction diode PD showed a responsivity of 15.6 A/W,an external quantum efficiency of 7626%,and a detectivity rate of 10¹⁵ Jones order of magnitude at a bias voltage of 10 V.（2）The photoconductive properties of ZnGa₂O₄ thin film photoconductive devices is further optimised by various post-processing methods.Firstly,the oxygen vacancy concentration of the ZnGa₂O₄ films was modulated by the fast annealing atmosphere,and the comparison revealed that the photoconductivity properties of the ZnGa₂O₄ films treated by fast annealing at 700°C in N₂ atmosphere were significantly improved compared with those of the untreated films.Secondly,the oxygen vacancy-related defects on the surface of the ZnGa₂O₄ films were further modulated by F plasma treatment,and the photoconductive properties of the ZnGa₂O₄ films treated with 15 min F plasma were better,and the photoconductive UV PD developed using them reached a responsivity of42.2 A/W.All these results suggest that the subsequent treatment is an effective way to further enhance the ultra-wideband UV detection of the oxide semiconductor.（3）On the basis of the effective modulation of the photovoltaic properties of n-type ZnGa₂O₄ thin films,two kinds of p-type spinel oxides,Ni Ga₂O₄ and Zn Co₂O₄,were used to construct p-n junctions with ZnGa₂O₄,respectively,in which a significant photovoltaic effect was observed in the all-spinel-structured Zn Co₂O₄/ZnGa₂O₄ p-n heterojunctions.In the photovoltaic（self-powered）mode,the p-n junction photodiode has a responsivity of 52.1 m A/W,a detectivity of 6.1×10¹² Jones,and the p-n junction photodiode has a fast photoresponsive characteristic both in the forward-biased,reverse-biased,and 0 V-biased states.The typical rise time（τ_r）constant is 138 ms,and the fall time（τ_d）constant is 20ms.The analysis of the interfacial energy band structure of Zn Co₂O₄/ZnGa₂O₄heterojunctionsshows that it is characterized by a type-II staggered arrangement,and this interfacial energy band structure provides a driving force for the separation and transport of the photogenerated electron-hole pairs,which is conducive to the improvement of the photoresponse characteristics of the device.（4）Based on the preliminary exploration of the development scheme of spinel oxide ultra-wideband semiconductor ZnGa₂O₄ solar-blind UV PD device,in order to evaluate the technical value of this all-spinel structure Zn Co₂O₄/ZnGa₂O₄ photodiode,this dissertation also constructed Si/ZnGa₂O₄ p-n heterojunction,characterized Si/ZnGa₂O₄hetero-interfacial energy-band structure,and compared their UV detection performance parameters were compared.The results show that the Si/ZnGa₂O₄ heterointerfacial energy band structure is a type I straddle-riding arrangement,and the performance indexes of responsivity and detectivity in photovoltaic mode are poorer than those of the ZnGa₂O₄/Zn Co₂O₄ photodiodes,which may be related to the weaker built-in electric field established by its interfacial type I straddle-riding energy band structure.（5）Based on the comparison of the UV detection performance with Si/ZnGa₂O₄p-n heterojunction photodiodes,in order to more comprehensively evaluate the technical value of the all-spinel-structured Zn Co₂O₄/ZnGa₂O₄ photodiodes,the amorphous ZnGa₂O₄/Ni O p-n heterojunction devices are further constructed in this dissertation.The energy band structure of the Si/ZnGa₂O₄ hetero-interface is also characterized,and a comprehensive comparison of the UV detection parameters was carried out.The results show that the energy band structure of the ZnGa₂O₄/Ni O heterojunction interface is also a type II staggered arrangement.Therefore,in the photovoltaic mode,the responsivity and detectivity performance indexes of the two heterogeneous p-n junction photodiodes,ZnGa₂O₄/Zn Co₂O₄ and ZnGa₂O₄/Ni O,are comparable,but the amorphous ZnGa₂O₄/Ni O photodiode is slightly faster,with its typical rise time（τ_r）constant of 48 ms and a fall time（τ_d）constant of 22 ms.This may be related to the crystallization quality of the ZnGa₂O₄and Zn Co₂O₄ materials grown on the sapphire substrate.Subsequent work is using Mg Al₂O₄ spinel single crystals with good lattice fitness as the substrate to construct ZnGa₂O₄/Zn Co₂O₄ heterojunction devices,which has the potential to further improve the comprehensive performance index of ZnGa₂O₄/Zn Co₂O₄ heterojunction UV detection.