Graphene/SrTiO₃ interface-based UV photodetectors with high responsivity

Strontium titanate (SrTiO₃), which is a crucial perovskite oxide with a direct energy band gap of 3.2 eV, holds great promise for ultraviolet (UV) photodetection. However, the response performance of the conventional SrTiO₃-based photodetectors is limited by the large relative dielectric constant of the material, which reduces the internal electric field for electron-hole pair separation to form a current collected by electrodes. Recently, graphene/semiconductor hybrid photodetectors by van-der-Waals heteroepitaxy method demonstrate ultrahigh sensitivity, which is benefit from the interface junction architecture and then prolonged lifetime of photoexcited carriers. Here, a graphene/SrTiO₃ interface-based photodetector is demonstrated with an ultrahigh responsivity of 1.2× 10⁶ A/W at the wavelength of 325 nm and ∼ 2.4× 10⁴ A/W at 261 nm. The corresponding response time is in the order of ∼ ms. Compared with graphene/GaN interface junction-based hybrid photodetectors, ∼ 2 orders of magnitude improvement of the ultrahigh responsivity originates from a gain mechanism which correlates with the large work function difference induced long photo-carrier lifetime as well as the low background carrier density. The performance of high responsivity and fast response speed facilitates SrTiO₃ material for further efforts seeking practical applications.