Self-Powered Photodetectors Based on Core–Shell ZnO–Co3O4 Nanowire Heterojunctions

Self-powered photodetectors operating in the UV-visible-NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation without external power sources. In this study, we propose a new p-n junction nanostructure, based on a ZnO-Co3O4 core-shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV-visible-NIR p-n heterojunction photodetector. Ultrathin Co3O4 films (in the range 1-15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al2O3 buffer layer between ZnO and Co3O4 was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO-Al2O3-Co3O4 system at zero bias is 6 times higher compared to that of ZnO-Co3O4. The responsivity ( R) and specific detectivity ( D*) of the best device were 21.80 mA W-1 and 4.12 × 1012 Jones, respectively. These results suggest a novel p-n junction structure to develop all-oxide UV-vis photodetectors based on stable, nontoxic, low-cost materials.