Design,Fabrication And Characterization Of MgGa₂O₄ Solar-blind Ultraviolet Photodetectors

Due to its advantages of low background noise,high sensitivity,and strong anti-interference ability,solar-blind ultraviolet photodetectors have great application prospects in military and civilian fields such as missile warning,space security communications,environmental monitoring,and fire monitoring.Spinel-type complex oxide magnesium gallate（MgGa₂O₄）is a typical ultra-wide band gap semiconductor,which not only has ultra-wide band gap（～4.9 e V）,high thermal and chemical stability,strong radiation resistance As well as good mechanical properties,the electrical properties of the material can also be effectively controlled by adjusting the anti-site defects of Mg and Ga cations.These excellent properties make MgGa₂O₄materials show great potential in fabricating high-performance solar-blind UV photodetectors.For a long time,people have regarded MgGa₂O₄ as a pure and excellent light-emitting material.Only a few semiconductor devices of MgGa₂O₄ have been reported,including gas sensors,spintronic devices,etc.The research on MgGa₂O₄optoelectronic devices is almost blank.In view of the huge development potential of MgGa₂O₄ materials in the field of solar-blind UV photodetection,this thesis aims to develop high-performance MgGa₂O₄ solar-blind UV photodetectors,focusing on metal-organic compound chemical vapor deposition（MOCVD）epitaxial growth and film annealing of MgGa₂O₄ thin films.The optimization of the process,the regulation of the Mg ion content,the preparation of the corresponding UV detectors,and the optimization of the device structure are carried out.The specific contents include:（1）A spinel-structured MgGa₂O₄ film was prepared on a c-plane sapphire substrate by MOCVD,and the film was annealed at high temperature in different atmospheres.On this basis,a planar metal-semiconductor-metal（MSM）solar-blind UV photodetector was fabricated.By comparing the properties of three MgGa₂O₄ thin films annealed in native,O₂ atmosphere and N₂ atmosphere and their photodetector performances,it is found that high temperature annealing treatment can improve the crystalline quality of MgGa₂O₄ thin films,thereby significantly improving the performance of the device.Among them,O₂ atmosphere annealed devices have the lowest dark current,the highest UV-Vis suppression ratio,and the fastest response speed,which are related to the effective reduction of oxygen vacancy defect density in thin films by O₂atmosphere annealing.（2）The effects of annealing temperature and annealing time on film properties under O₂ atmosphere were further studied,and it was found that MgGa₂O₄ films annealed at900℃for 15 min had higher crystalline quality.Based on this thin film,a self-powered MgGa₂O₄ solar-blind UV detector with a planar asymmetric Schottky structure was fabricated.The device has a peak responsivity of about 3.3 m A/W at 0V and a UV-Vis rejection ratio(R_peak/R_{400 nm})of about 10⁴and has a very fast response speed.（3）Mg_xGa₂O₄ epitaxial films with different Mg compositions were prepared by MOCVD by regulating the flow rate of Mg source,and the x was 0.6,0.8,1,1.1 and1.4,respectively.X-ray diffraction test results show that all samples maintain the spinel structure of MgGa₂O₄.Based on the above films,a solar-blind UV photodetector with MSM structure Mg_xGa₂O₄ was prepared.Among them,the device with x=1 MgGa₂O₄ film has the highest responsivity.As the Mg composition deviates from the stoichiometric ratio,the photodetection performance of the detector tends to decrease.