Ultrahigh-Performance Solar-Blind Photodetector Based on a-Phase-Dominated Ga2O3 Film with Record Low Dark Current of 81 fA

$\alpha $ -phase-dominated Ga2O3 films were hete- roepitaxially grown on ${c}$ -plane sapphire substrate by metal-organic chemical vapor deposition (MOCVD), followed by the fabrication of ultraviolet (UV) photodetectors (PDs) with a metal-semiconductor-metal (MSM) structure using a Ti/Au metal stack as the electrode in an interdigitated geometry. The PDs possess a record low dark current of 81 fA under a bias voltage of 12 V, with a high sensitivity as confirmed by a record high photo-to-dark-current ratio exceeding 107 under 254 nm light illumination. Furthermore, the PDs also exhibit a high responsivity and the photoconductive gain of 11.5 A/W and 55, respectively. Most importantly, it shows an ultrahigh detectivity of ${1.0} \times {10}^{{15}}$ Jones with a quite fast response of 42ms, paving the way for advancement of next-generation PD applications.