Visible Light Response of Unintentionally Doped ZnO Nanowire Field Effect Transistors

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 ( V T ) 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 N 2, and pure O 2 ) and with/without nanowire surface modifications (coated with PMMA).