Enhanced performance in SnO$_{\mathrm{2}}$ thin film UV photodetectors via self-assembled CuO/SnO$_{\mathrm{2}}$ nanoheterojunctions

Low-cost visible-blind ultraviolet (UV) photodetectors (PDs) are of interest for versatile applications in digital imaging, optical communications, and biomedical sensing. We report on the use of CuO/SnO$_{\mathrm{2}} \quad p-n$ nanoscale heterojunctions to enhance the performance of SnO$_{\mathrm{2}}$ thin film UV PDs. Our method produces robust structures that operate at low bias without complex fabrication processes. The nanoheterojunctions are self-assembled by sputtering Cu clusters that oxidize in ambient to form CuO nanoparticles. The chemical identity, morphology and distribution of the nanoparticles are investigated through high-resolution XPS and AFM characterization. Enhanced UV absorption is demonstrated both experimentally and using optical simulations after addition of the CuO/SnO$_{\mathrm{2}}$ nanoheterojunctions. The device performance improvements are attributed to the strong absorption in the CuO nanoparticles and electron transfer facilitated by the nanoheterojunctions. The PDs show a five-fold increase in peak responsivity at 0.2 V bias. The photoresponse factor, defined as the wavelength-dependent ratio between the photocurrent and dark current, was estimated to be 592 for the CuO-SnO$_{\mathrm{2}}$ PD under 290 nm illumination.