ZnO-based p-i-n and n-i-p heterostructure ultraviolet sensors: a comparative study

A comparative study is reported on p-NiO∕i-ZnO∕n-ITO and n-ITO∕i-ZnO∕p-NiO heterostructure ultraviolet sensors. In comparing reverse-bias current-voltage characteristics, dark current transients, and dark-current field dependence of both diodes, we observed that thermal and Poole–Frenkel generation currents dominate in the leakage. The difference in the leakage level and field dependence essentially depends on the p-i interface. Analysis of forward-bias current-voltage characteristics identifies the difference in Schottky barrier height between two diodes, which causes the difference in the contact leakage level as well. Furthermore, the p-i-n diode has better performance in photosensitivity and responsivity due to less optical loss in the top contact, and both diodes are promising for low levels of ultraviolet detection.