Reduced Graphene Oxide/Se Microtube p–p Heterojunction for Self-Powered UV–NIR Broadband Photodetectors

The broadband (UV–vis–NIR) photodetectors (PDs) based on reduced graphene oxide (RGO) with high carrier mobility have the potential to expand the application of optical devices. In this report, the new p–p Se/RGO heterojunction combined with RGO nanosheets and a highly crystalline p-type selenium microtube (Se-MT) was prepared by the simple spin-coating approach. The Se-MT, with a maximum length of 3 mm, is beneficial to deposited electrodes at a low cost. The band gap of the RGO layer is controlled by low-temperature-annealed graphene oxide (GO) nanosheets. Both Se/RGO PD and Se/GO PD exhibit self-powered characteristics and have good responsivity, detectivity, and on/off ratio in a wide wavelength range of UV–NIR (280–1000 nm). Compared to pure Se-MT PD (11.8 mA W –1 and 1.09 × 10 9 jones), Se/RGO PD shows 14- and 135-times enhancement for the responsivity of 168.1 mA W –1 and the specific detectivity of 1.48 × 10 11 jones, especially at 368 nm without applied bias voltage, respectively. Se/RGO PD displays an on/off ratio of 1049 with a fast response speed of 18 μs/4.76 ms at every cycle. Remarkably, the responsivity of Se/RGO PD and Se/GO PD under 1000 nm irradiation is 19.5 and 12.1 mA W –1, respectively, with regard to 390 and 242 times larger than that of Se-MT PD (0.05 mA W –1 ). Due to the enhanced optical absorption of the RGO layer and improved band gap alignment to provide the high built-in field at the Se/RGO heterojunction that eventually results in the successful separation of the charge carriers, the outstanding self-powered operation has been demonstrated over the UV–NIR wavelength range. The findings show great promise for high-performance broadband devices with independent detection.