Transfer characteristic of zinc nitride based thin film transistors

Polycrystalline zinc nitride (Zn3N2) thin films were prepared on quartz and aluminum tin oxide /indium tin oxide (ATO/ITO) and SiO2-covered crystalline silicon by reactive pulsed laser ablation (PLD) of a metallic zinc target using a pulsed Nd:YAG laser, assisted by a 13.56 MHz radio-frequency (RF) nitrogen plasma. The microstructural, optical and electrical properties of the as-deposited films were studied by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), low-temperature photoluminescence (PL), optical transmittance, and field effect transistor I-V measurements. SEM revealed a compact and crack-free film surface. XRD study indicated that the Zn3N2 films deposited at 673 K substrate temperature were cubic, with lattice constant a = 0.97 nm and having no preferred orientation. PL spectra taken at 4.2 K show a 7-9 meV wide exciton-related peak at 3.59 eV. The optical absorption coefficient, estimated from the transmission spectra using Beer's law, was utilized to determine the optical band gap of the films. The Zn3N2 showed a direct band gap of similar to 3.2 eV at room temperature. Transparent field effect transistor structures with a 200 nm thick Zn3N2 film as active channel layer exhibited non-linear I-V transfer characteristics, which is typical of devices having a large density of interface trap states. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim