Surface state controlled ultrahigh selectivity and sensitivity for UV photodetectors based on individual SnO2 nanowires

For nanostructures with a large surface-to-volume ratio, quantities of dangling bonds can create affluent surface states due to the breaking of lattice periodicity on their surfaces. Herein, surface states are utilized for the development of high-performance photodetectors based on individual SnO2 nanowires. The photodetectors not only show ultrahigh selectivity and sensitivity to ultraviolet (UV) light of about 340 nm with and without bias, but also show weak response to sub-bandgap visible (VIS) and near infrared (NIR) light. Moreover, their detectivity is strongly dependent on externally applied bias voltage and illumination light intensity. The abundant surface states result in the formation of back-to-back diodes for two-terminal nanowire-based devices. The photoconductive mechanism is controlled by a photovoltaic effect of a surface state related reverse biased diode in contact with a negative electrode. Under light illumination, the efficient separation of photoexcited carriers at the Ag and SnO2 interface and the fast drift of electrons separated into the core of n-type SnO2 nanowires toward another end lead to ultrahigh gain, a large photo-to-dark current ratio, and high-speed response for the nanostructure photodetectors at a relatively high bias voltage. These results demonstrate that the surface states of nanostructures are promising for the development of high performance photodetectors, and meanwhile render an interpretation particularly valuable for the photoconductive mechanism of nanostructures.