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

TiO 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, the devices usually have large dark current (I ) and low light current (I ), which seriously reduces the sensitivity and responsivity (R) of the TiO based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO film to ameliorate these issues. Due to the difference of work function between TiO nanoparticles and C QDs, the built-in electric field (E ) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the I of the photodetector. Moreover, the E 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.