Visible Light Response of Unintentionally Doped ZnO Nanowire Field Effect Transistors

Abstract

A significant visible light response of unintentionally doped ZnO nanowire (NW) field effect transistors (FETs) has been observed in a reversible manner (for illumination source on and off). In particular, under white light illumination (wavelength longer than 400 nm), the threshold voltage (VT) of the ZnO NW FET shifts greatly to the negative direction, suggesting a remarkable increase in carrier concentration. A photon-assisted oxygen molecule desorption mechanism is proposed to explain the observed sub-bandgap photoresponse on the basis of the behavior of the experimental devices in different gas atmospheres (air, vacuum, pure N2, and pure O2) and with/without nanowire surface modifications (coated with PMMA).