Unraveling the mechanism of ultraviolet-induced optical gating in Zn1−xMgxO nanocrystal solid solution field effect transistors

Abstract

We report ultraviolet (UV)-induced optical gating in a Zn1−xMgxO nanocrystal solid solution (NCSS) field effect transistor (FET) through a systematic study in which UV-induced charge transport properties are probed as a function of Mg composition. Change in the electrical properties of Zn1−xMgxO NCSS associated with electronic traps is investigated by field effect-modulated current–voltage characteristic curves in the dark and under illumination. Under UV illumination, significant threshold voltage shift to a more negative value in an n-channel Zn1−xMgxO NCSS FET is observed. Importantly, as the Mg composition increases, the effect of UV illumination on the threshold voltage shift is alleviated. We found that threshold voltage shift as a function of Mg composition in the dark and under illumination is due to difference in the deep trap density in the Zn1−xMgxO NCSS. This is supported by Mg composition dependent photoluminescence intensity in the visible range and reduced FET mobility with Mg addition. The presence of the deep traps and the corresponding trap energy levels in the Zn1−xMgxO NCSS are ensured by photoelectron spectroscopy in air.