Self-powered UV-visible photodetector with fast response and high photosensitivity employing an Fe:TiO2/n-Si heterojunction

An ultrasensitive, fast response and self-powered photodetector would be preferable in practical applications. In this paper, we report fast response, high photosensitivity and self-powered Fe doped TiO2 (Fe: TiO2)/n-Si UV-visible detectors via a facile solution process. As-fabricated devices exhibited excellent photoresponse properties, including high responsivity of 46 mA W-1 (350 nm) and 60 mA W-1 (600 nm) with 0.5 mW cm(-2) light irradiation under zero bias, as well as an ultrasensitive (on/off ratio up to 103), fast (rise/decay time of < 10/15 ms), and broad-band (UV-visible) photodetection with no or low external energy supply. Furthermore, the quantum efficiency of the heterojunction rose up beyond 100% with a broad wavelength range at a small reverse bias of -0.5 V. The self-power originated from the existence of a built-in electric field between Fe: TiO2 and Si that helps facilitate the separation of photogenerated electron-hole pairs and regulate the electron transport. Capacitance-voltage (C-V) measurements of Fe: TiO2/n-Si devices also confirmed the existence of the built-in electric field. Such Fe: TiO2/n-Si heterojunction photodetectors might be potentially useful for relative applications with weak-signal fast detection in the UV-visible band.