Optically transparent ZnO-based n–i–p ultraviolet photodetectors

An optically transparent tin-doped indium oxide/ZnO/NiO n–i–p heterostructure photodiode was fabricated by ion beam assisted e-beam evaporation. The diode clearly demonstrates rectifying current–voltage (J–V) characteristics with a current rectification ratio up to 104 at bias ± 2 V and a low reverse current of ∼ 100 nA/cm2 at − 5 V. Analysis of J–V characteristics including time dependence of the dark current shows that the leakage current at low biases is attributed to thermal generation via defect states, and at high biases, field-enhanced carrier generation from the ZnO layer dominates. Spectral response and linearity measurements indicate that such a diode is particularly suitable for low level of ultraviolet detection.