Built-in electric field promotes photoexcitation separation and depletion of most carriers in TiO ₂ :C UV detectors

Abstract

Abstract TiO 2 has been widely used in ultraviolet (UV) photodetectors, but due to the large number of structural defects and strong band-to-band recombination of the exciton in TiO 2 , the devices usually have large dark current ( I d ) and low light current ( I l ), which seriously reduces the sensitivity and responsivity ( R ) of the TiO 2 based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO 2 film to ameliorate these issues. Due to the difference of work function between TiO 2 nanoparticles and C QDs, the built-in electric field ( E bi ) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO 2 film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the I d of the photodetector. Moreover, the E bi and depletion region will also contribute to the faster charge collection under UV illumination and recombination of the electron in dark, which is beneficial for the improved response/recovery speed of the device.