Gallium Oxide Based Solar-blind Ultraviolet Photodetectors

Ultraviolet?UV?photodetectors have many civil and military applications such as biological/chemical analysis,flame sensing,covert space-to-space communications,missile tracking and environmental monitoring.Due to the strong absorption of deep UV light by ozone,particles,and water vapor in the atmosphere,the solar irradiation with wavelength shorter than 280 nm is almost non-existent at the surface of the earth,which is called solar-blind range.Owing to the low natural background in the solar-blind region,photodetectors operating in this spectral range have high signal-to-noise ratio and low false alarm rate.Unfortunately,the commercially available solar-blind photodetectors are usually photomultiplier tubes which are bulky,fragile,and require large bias voltage,thus limiting their applications.The advantages of wide-band-gap?WBG?semiconductors,such as high radiation hardness and intrinsicvisible/solarblind,haveopenedthepossibilityofdeveloping high-performance WBG solar-blind UV photodetectors,which are recognized as the potential alternative for the photomultiplier tubes.In recent years,a large variety of WBG semiconductors have been investigated to design solar-blind photodetectors,including Al_xGa_1-xN,Zn_xMg_1-xO,gallium oxide?Ga₂O₃?and diamond,etc.The bandgap of Ga₂O₃ is usually between 4.4 and 5.1 eV,and the corresponding absorption cutoff wavelength is about 250²80 nm.It is a promising candidate for UV detectors with intrinsic solar blind selectivity.However,the reported Ga₂O₃ based photodetectors is still far below expection.The low performance of photodetectors such as low responsivity and slow response speed restricts the application of Ga₂O₃ in the field of solar-blind detection.This work is focused on fabricating high-performance Ga₂O₃ based solar-blind UV detectors.The following results have been achieved:?1?A self-powered solar blind UV detector using a diamond/Ga₂O₃ heterostructure was proposed.The Ga₂O₃ film was deposited by plasma chemical vapor deposition on a high quality diamond wafer synthesized by microwave plasma chemical vapor deposition.Thediamond/Ga₂O₃heterojunctiondevicewasconstructed.Diamond/?-Ga₂O₃heterojunctionshavebeenfabricated,andsolar-blind photodetectors have been constructed from the heterojunctions.The photodetectors have obvious rectification characteristics and can work well without any external power supply.The peak responsivity at 244 nm is about 0.2 mA W^-1under zero bias.The UV/visible rejection ratio is more than two orders of magnitude with a sharp cutoff wavelength at 270 nm,indicating that the photodetector response mainly to the solar-blind signals.As a self-powered device,the photodetector can operate repeatability and stability at zero bias.More importantly,high quality images have been obtained by using the self-powered photodetector as a sensing pixel of an imaging system.?2?A 4×4 photodetector array has been constructed from Ga₂O₃ films,and each cell is constituted by a Metal-Semiconductor-Metal structured photodetector.The photodetector cells exhibit a low dark current of 4.0×10^-10A,and their peak responsivity at 256 nm is about 1.2 A W^-11 when the bias is 10 V.The UV/visible rejection ratio is more than 4 orders of magnitude with a sharp cutoff wavelength at265 nm,indicating that the photodetector cells have a relatively high spectral selectivity to solar-blind ultraviolet.The 16 photodetector cells show high uniformity,and clear images can be obtained employing the photodetector array as sensing units.