Study On Gallium Oxide And Gallium Indium Oxide Photodetectors

Gallium oxide is a new generation of ultra-wide band-gap semiconductor.Due to its ultra-wide band gap,good radiation resistance,physical and chemical stability,its cut-off wavelength falls in the sun-blind ultraviolet band,which has a very broad application prospect in the field of photodetectors.Metal-semiconduction-metal（MSM）photodetectors have the advantages of simple structure,easy preparation,low cost,and mass production.Gallium oxide MSM photodetectors have become the focus of attention.Undoped gallium oxide has a limited detection range in solar blind ultraviolet band,while indium doping can regulate the band gap width of gallium oxide and extend the spectral response range of photodetectors.In this paper,gallium oxide and gallium indium oxygen films and their photodetectors were prepared by magnetron sputtering and post-annealing technology.The effects of post-annealing temperature,post-annealing atmosphere,and electrode materials on the performance of detectors were studied.The main research content and innovation points of this paper are summarized as follows:（1）The formation energy,crystal structure,band gap width,state density,and optical properties of In-dopedβ-Ga₂O₃ are calculated using the first principles based on density functional theory（DFT）.The results show that the lattice constants a,b,and c increase almost linearly and the band gap width decreases linearly with the increase of In doping concentration.The total state density moves towards the lower energy direction,while the peak value increases continuously.The highest peak value of the real part of the dielectric function decreases gradually and moves towards the low energy direction,while the local peak value of the imaginary part moves towards the low energy region.The absorption edge of the optical absorption coefficient decreases from 4.9e V to 4.2e V,and the absorption cutoff wavelength increases from 254nm to 293nm.The simulation results provide a theoretical basis for the subsequent preparation of gallium oxide and gallium indium oxygen thin films.（2）Ga₂O₃ films and their photodetectors were prepared by magnetron sputtering and post-annealing technology under different annealing temperatures and atmospheres.The analysis results show that under the same annealing atmosphere at different annealing temperatures,the increase of annealing temperature can improve the crystal quality,increase the band gap width（4.92e V～5.08e V）and increase the red light intensity of the films.In the same annealing temperature and different annealing atmospheres,compared with Air annealing atmospheres,the crystal quality of films in Ar,N_2,and O₂ annealing atmospheres is better,and the band gap width of films is about 4.9e V.Greenlight intensity decreases in the Ar,N₂,Air,and O₂ annealing atmospheres in turn.Ti/Au electrodes were grown on the surface of the prepared film,and the photodetector was prepared.The results of I-V and I-T curves show that increasing annealing temperature can increase the photodetector’s light-dark current ratio at 254nm wavelength light source,improve the responsivity and detectivity,and reduce the response time.Under the same annealing temperature and different annealing atmospheres,N₂,Air,and O₂ annealing atmospheres can increase the photodetector’s light-dark current ratio,improve responsiveness and reduce response time compared with Air annealing atmospheres.This is related to the crystal quality of the film and the concentration of oxygen vacancy in the film.（3）(Ga_0.7In_0.3)₂O₃ films with different annealing atmospheres were prepared by magnetron sputtering and post-annealing.The photodetectors with different electrodes in the same annealing atmosphere and the same electrodes in different annealing atmosphere were prepared.The results show that the films annealed in Air atmosphere have the best crystal quality,the band gap width of the films is about 4.3e V,and the optical absorption edge is about 285nm.Photodetectors with Cu,Ti/Au,Al,Ag,and Au electrodes were prepared by thin films annealed in Air atmosphere,and photodetectors with Al electrodes were prepared by thin films annealed in Ar,N_2,and O₂ atmosphere.The results of the I-V curve and I-T curve analysis show that the photodetectors with Al electrode(Ga_0.7In_0.3)₂O₃ have the highest light-dark current ratio and the best responsiveness and detectivity under the same annealing temperature and different electrode conditions.This is because there is a small difference between the work function of the Al electrode and the electron affinity of the semiconductor.Under the same electrode condition in different annealing atmospheres,the detectors annealed in Ar and N₂ atmospheres have lower light-dark current ratio,responsivity and detectivity,and longer switching time.This is because oxygen atoms in the film are further precipitated under Ar and N₂atmosphere annealing,resulting in increased oxygen vacancy and enhanced conductivity of the film.