Fully transparent vertically aligned ZnO nanostructure-based ultraviolet photodetectors with high responsivity

This study describes the fabrication of fully transparent ultraviolet (UV) photodetectors with high responsivities remarkably enhanced by introducing thin insulating MgO (i-MgO) layers, highly dense ZnO nanostructures, and the direct contact of the ITO electrode with the nanostructures. The i-MgO layers and the ZnO nanostructures were grown by metal organic chemical vapor deposition, and the morphology of the ZnO nanostructures exhibited structural transitions (nanowires → nanowalls → films) depending on the thickness of the MgO layers. For the construction of a fully transparent device structure, the whole surface of the nanostructures was covered with two dimensional ITO top electrodes. The sample with a 12 nm thick i-MgO layer had high-density nanowall structures and exhibited a dramatically improved UV photo-detecting performance (photo-to-dark current ratio of 7143, recovery time of 220 ms, responsivity of 290 A/W, and high transmittance of approximately 90% in the visible region). A detailed discussion regarding the fully transparent UV photo-detecting mechanism developed by the i-MgO layers and highly dense nanostructures is presented in this work.