Tunable Ultraviolet Photoresponse in Solution-Processed p–n Junction Photodiodes Based on Transition-Metal Oxides

Abstract

Solution-processed p–n heterojunction photodiodes have been fabricated based on transition-metal oxides in which NiO and ternary Zn_1–<i>x</i>Mg_<i>x</i>O (<i>x</i> = 0–0.1) have been employed as p-type and n-type semiconductors, respectively. Composition-related structural, electrical, and optical properties are also investigated for all the films. It has been observed that the bandgap of Zn_1–<i>x</i>Mg_<i>x</i>O films can be tuned between 3.24 and 3.49 eV by increasing Mg content. The fabricated highly visible-blind p–n junction photodiodes show an excellent rectification ratio along with good photoresponse and quantum efficiency under ultraviolet (UV) illumination. With an applied reverse bias of 1 V and depending on the value of <i>x</i>, the maximum responsivity of the devices varies between 0.22 and 0.4 A/W and the detectivity varies between 0.17 × 10¹² and 2.2 × 10¹² cm (Hz)^1/2/W. The photodetectors show an excellent UV-to-visible rejection ratio. Compositional nonuniformity has been observed locally in the alloyed films with <i>x</i> = 0.1, which is manifested in photoresponse and X-ray analysis data. This paper demonstrates simple solution-processed, low cost, band tunable photodiodes with excellent figures of merit operated under low bias