Conduction mechanism modulation in ZnO nanowire networks for enhanced UV photosensitivity

Abstract

The performance of ultraviolet (UV) photodetectors based on random networks of zinc oxide (ZnO) nanowires is strongly influenced by the degree of nanowire interconnectivity, which affects both charge transport and photoresponse dynamics. In ZnO networks, conduction over nanowire–nanowire tunnel junctions is modulated by rapid chemisorption–desorption of surface-bound oxygen, but experimental validation of the direct effect of surface photochemistry on conduction mechanisms has remained limited. The work presented in this paper reveals a transition in the dominant transport mechanisms that govern transport in ZnO nanowire networks from Poole Frenkel-type field assisted emission of trapped charges in the dark to space–charge limited current upon UV exposure driven by the removal of oxygen induced charge traps. The easily manufacturable and readily scalable metal–semiconductor–metal photodetectors achieve a specific on/off ratio of up to 4.5×106cm−2 and photoresponse times of ∼4 (rise) and 6s (fall). These findings establish a direct link between surface photochemistry and charge transport in ZnO nanowire networks and demonstrate that controlling percolation and tunneling distances is crucial for optimizing both the sensitivity and temporal response of UV photodetectors. The presented approach provides practical guidelines for developing advanced, responsive UV sensing technologies.