Highly sensitive, ultra-low dark current, self-powered solar-blind ultraviolet photodetector based on ZnO thin-film with an engineered rear metallic layer

Abstract

International audienceIn this paper, novel self-powered, solar-blind UV photodetector (PD) designs based on a ZnO thin-film with engineered back metal layer (BML) were fabricated by RF magnetron sputtering and e-beam evaporation techniques. An exhaustive study concerning the impact of dissimilar BML (Au and Ni) on the device structural, optical and electrical properties was carried out. The measured I–V curves illustrated an asymmetrical behavior, enabling a clear and distinctive photovoltaic mode. Superb sensitivity of 107, high ION/IOFF ratio of 149dB, ultralow dark-noise current less than 11pA and responsivity exceeding 0.27A/W were reached for the prepared ZnO-based UV-PDs in self-powered mode. The role of the engineered BML in promoting effective separation and transfer of the photo-induced carriers was discussed using the band-diagram theory. The influence of the annealing process on the UV-sensor performance was also investigated. The annealed device at 500°C demonstrated a lower dark current of a few picoamperes and a high rejection ratio of 2.2:103, emphasizing its exciting visible blindness characteristics. Therefore, the use of an engineered BML with optimized annealing conditions open up new perspectives to realizing high-performance, self-powered solar-blind UV-PDs based on simple thin film-ZnO structure strongly desirable for various optoelectronic applications