Research On New Structure Of Metal-Oxide Semiconductor Photodetectors

Recently,UV detectors have attracted extensive attention for widespread civil and military applications,such as missile tracking,short-range secure communication and ozone holes monitoring.Several wide band-gap semiconductors have been employed to fabricate UV detector.With high chemical stability,high mechanical strength,high breakdown electric field and especially a band-gap of 4.9 eV,gallium oxide is considered to be one of the ideal candidates for optoelectronic devices.The fabrication of high-responsivity and high-detectivity?-Ga₂O₃-based UV detector poses severe challenges in thin film epitaxial growth.In addition,substrate selection plays an important role for hetero-epitaxial growth of gallium oxide thin films.In order to obtain high-quality?-Ga₂O₃ thin films and high-responsivity and high-detectivity?-Ga₂O₃-based UV detector,in this work,Sn-doped?-Ga₂O₃ thin films?abbreviated as Sn:?-Ga₂O₃?were deposited on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy.The performance of UV detectors made from Sn:?-Ga₂O₃ was studied.The distinctions of photoelectric properties of UV detectors made from?-Ga₂O₃ thin films grown on sapphire substrates with different single crystal orientations were investigated.The details are as follows:?1?Sn:?-Ga₂O₃ has good electrical conductivity.The metal-semiconductor-metal?MSM?photodetector made from Sn:?-Ga₂O₃ has more excellent photoelectric performance,including photo-current,responsivity and comprehensive performance parameter index detectivity.However,due to the deterioration of the thin films'crystal quality by doping,the time-dependent response of the photodetector made from Sn:?-Ga₂O₃ became worse.The decay time is 4.2 s,with serious sustained photoconductive effects.In order to improve the time-dependent response,in this work,a multi-layer thin-film structure was constructed by Sn:?-Ga₂O₃ and unintentionally doped?-Ga₂O₃ thin films?abbreviated as?-Ga₂O₃?.The photo-current to dark-current ratio of photodetectors made from multi-layer thin films has been greatly improved,but their detectivity has decreased.Compared with the photodetector made from Sn:?-Ga₂O₃,the photo-current to dark-current ratio of the photodetector made from?-Ga₂O₃/Sn:?-Ga₂O₃/?-Ga₂O₃sandwich-structure thin films was increased from 901 to 3080.The decay time of the photodetector made from sandwich-structure thin films was reduced from 4.2 s to 0.7 s,and its sustained photoconductive effects were effectively suppressed.Comprehensively considering the characteristic parameters of photo-current to dark-current ratio,detectivity and time-dependent response,?-Ga₂O₃/Sn:?-Ga₂O₃/?-Ga₂O₃ sandwich-structure thin films are more suitable for UV detectors.?2?The microstructure and photoelectric properties of?-Ga₂O₃ thin films grown on c-plane and r-plane sapphire substrates were studied.?2^<sub>01?-oriented?-Ga₂O₃ thin films were grown on c-plane sapphire.While,the?-Ga₂O₃ thin films grown on r-plane sapphire were composed by both?100?and?001?oriented grains of?-Ga₂O₃ parallel to the substrate surface.Compared with the?-Ga₂O₃ thin film grown on c-plane sapphire,although the crystal orientation of the?-Ga₂O₃ thin film grown on r-plane sapphire is not single,it has better photoelectric performance.The responsivity and detectivity of the photodetectors made from?-Ga₂O₃ thin films grown on r-plane sapphire are about 170A/W and 1.3×10¹⁴ Jones respectively,which are almost two-times larger than those of the photodetectors made from?-Ga₂O₃ thin films grown c-plane sapphire.So,the r-plane sapphire is also an excellent substrate candidate for?-Ga₂O₃ thin film and solar-blind UV detectors.