Localized Tail States and Electron Mobility in Amorphous ZnON Thin Film Transistors

Abstract

The density of localized tail states in amorphous ZnON (a-ZnON) thin film transistors (TFTs) is deduced from the measured current-voltage characteristics. The extracted values of tail state density at the conduction band minima (N tc) and its characteristic energy (kT t) are about 2 × 10 20 cm -3 eV -1 and 29 meV, respectively, suggesting trap-limited conduction prevails at room temperature. Based on trap-limited conduction theory where these tail state parameters are considered, electron mobility is accurately retrieved using a self-consistent extraction method along with the scaling factor '1/(α + 1) associated with trapping events at the localized tail states. Additionally, it is found that defects, e.g. oxygen and/or nitrogen vacancies, can be ionized under illumination with hv ‰" Eg, leading to very mild persistent photoconductivity (PPC) in a-ZnON TFTs.