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 x 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 x 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 mu s/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.