Preparation Of Highly Transparent ?-Ga₂O₃ Thin Films And Study On Its Solar-blind Ultraviolet Photodetectors

Solar-blind ultraviolet?UV?photodetectors?PDs?are widely used in military and civil fields such as flame monitoring,high-voltage corona,chemical/biological analysis,ozone hole detection,missile guidance and space secure communications due to the advantages of low background noise and high sensitivity.In recent years,with the rapid development of semiconductor materials and technology,the use of ultra-wide band gap semiconductor materials?Al Ga N,Zn Mg O,Ga₂O₃ and diamond?for the development of high-performance solar blind UV PDs has become a research hotspot in the field of photoelectric detection.Among them,?-Ga₂O₃,a new type of ultra-wide band gap semiconductor material with direct band gap??4.9 e V?and excellent physical and chemical properties,has been widely concerned by domestic and foreign researchers.Moreover,?-Ga₂O₃ is one of the ideal candidate materials for the development of solar blind UV PDs.At present,however,the solar-blind PDs based on?-Ga₂O₃ thin films mainly have problems in low responsivity and slow response speed,especially the high responsivity and fast response time are difficult to achieve simultaneously,which limits the commercial application of the device in military and civil fields.Aiming at the above problems,this paper is focused on fabricating high performance?-Ga₂O₃ based solar-blind ultraviolet PDs,and the main research results obtained are as follows:?1?Preparation of highly transparent?-Ga₂O₃ thin film and preliminary study of solar-blind ultraviolet photodetector.The?-Ga₂O₃ films were prepared on c-plane sapphire substrates by radio frequency magnetron sputtering and post-annealing.The effect of sputtering powers on the structural,optical and elemental compositions of?-Ga₂O₃ films were systematically studied.The results show that all?-Ga₂O₃ films exhibit preferential growth in the?-201?direction,and the growth rate of the film increases linearly and the crystal quality gradually becomes better with the increase of sputtering power.Meanwhile,all the?-Ga₂O₃ films exhibit extremely high average transmittance of 95%in UV-Vis region,exhibiting excellent optical properties.In addition,the lower the sputtering power,the larger the bandgap of the?-Ga₂O₃ film due to the Al diffusion from the substrates.A metal-semiconductor-metal?MSM?structured solar-blind photodetector based?-Ga₂O₃ film with optimal structural and optical properties was preliminarily fabricated.The device has excellent solar-blind ultraviolet characteristics,including a high light-dark ratio?>10³?,and faster response time?0.31/0.05s?.?2?Research on high-performance?-Ga₂O₃ based solar blind UV PDs based on the regulation of oxygen vacancy defects.In this work,amorphous Ga₂O₃ films were deposited on c-plane sapphire substrates by radio frequency magnetron sputtering,and the?-Ga₂O₃ films were prepared by post annealing treatment.The effect of annealing temperature on the structural,optical and elemental compositions of Ga₂O₃ films were systematically studied.The results show that both the amorphous and?-phase Ga₂O₃films exhibit ultra-high transmittance?>95%?in the near ultraviolet-Visible region.The crystal quality of?-Ga₂O₃ films gradually improved,and the width of the bandgap gradually increased with the increase of annealing temperature.Moreover,the post-annealing can effectively regulate the oxygen vacancies concentration in the films,which gradually decreases with the increase of annealing temperature.On this basis,the solar-blind UV photodetectors with MSM structure were fabricated for Ga₂O₃ films annealed at different temperatures.It was found that the device fabricated by amorphous Ga₂O₃ thin film has high responsivity but slow response time;in contrast,the?-Ga₂O₃thin films photodetectors with higher annealing temperature have fast response time,but lower responsivity.Interestingly,the performance indexes of relatively low-temperature annealed?-Ga₂O₃ film based photodetector is relatively comprehensive.This study found that the concentration of oxygen vacancies in the Ga₂O₃ films determines the performance of the photodetectors,and the effective control of oxygen vacancies defects is an effective method for developing solar-blind photodetectors with comprehensive performance.