Pt/ZnGa₂O₄/p-Si Back-to-Back Heterojunction for Deep UV Sensitive Photovoltaic Photodetection with Ultralow Dark Current and High Spectral Selectivity

In this work, a strategy of constructing a back-to-back heterojunction is proposed to fabricate Si-based photovoltaic photodetectors with high deep ultraviolet (DUV) spectral selectivity. By combining Pt with a thickness of 4 nm with a ZnGa2O4/Si heterojunction, a back-to-back heterojunction is successfully constructed. Based on that, a Pt/ZnGa2O4/p-Si DUV photovoltaic detector with a low dark current density (∼9.6 × 10–5 μA/cm2), a large photo-to-dark current ratio (PDCR, >105), and a fast response speed (decay time <50 ms) is fabricated. At 0 V bias, this device displays a photoresponsivity of about 1.36 mA/W and a high deep ultraviolet–visible (DUV–vis) rejection ratio (R258 nm/R420 nm) of ∼1.1 × 105, which are 1–2 orders of magnitude higher than those of most photovoltaic DUV detectors reported currently. Even at a working temperature of 470 K, the detectivity of this device can still reach ∼1.23 × 1010 Jones. In addition, compared with Au/ZnGa2O4/Si devices, the dark current and PDCR of this Pt/ZnGa2O4/Si device decrease by 2 orders of magnitude and increase by 1 order of magnitude, respectively. The enhanced performance of this ZnGa2O4/Si device can be attributed to the higher Schottky barrier established between Pt with a higher work function and ZnGa2O4. This strategy of adopting a back-to-back heterojunction device structure to hinder the visible light photoresponse of Si-based photodetectors and thus to reduce the dark current of a device can provide a reference for preparing photovoltaic DUV detectors with excellent performance.