Effects of Fluorine Doping on the Electrical Performance of ZnON Thin-Film Transistors

In this work, the effects of fluorine incorporation in high mobility zinc oxynitride (ZnON) semiconductor are studied by both theoretical calculations and experimental evaluation of thin film transistors (TFTs). From density functional theory (DFT) calculations, fluorine acts as a carrier suppressor in the ZnON matrix when it substitutes a nitrogen vacant site (V_N). Thin films of ZnON and ZnON:F were grown by reactively cosputtering Zn metal and ZnF₂ targets, and their electrical, physical, and chemical characteristics were studied. X-ray photoelectron spectroscopy (XPS) analyses of the nitrogen 1s peaks in ZnON and ZnON:F suggest that as the fluorine incorporation increases, the relative fraction of Zn-N bonds from stoichiometric Zn₃N₂ increases. On the other hand, the Zn-N bond characteristics arising from nonstoichiometric Zn_xN_y and N-N bonds decrease, implying that indeed fluorine anions have an effect of passivating the N-related defects. The corresponding TFTs exhibit optimum transfer characteristics and switching ability when approximately 3.5 atomic percent of fluorine is present in the 40 nm thick ZnON:F active layer.