Facile Phase Control of Multivalent Vanadium Oxide Thin Films (V2O5 and VO2) by Atomic Layer Deposition and Postdeposition Annealing

Atomic layer deposition was adopted to deposit VOx thin films using vanadyl tri-isopropoxide {VO[O(C3H7)]3, VTIP} and water (H2O) at 135 °C. The self-limiting and purge-time-dependent growth behaviors were studied by ex situ ellipsometry to determine the saturated growth conditions for atomic-layer-deposited VOx. The as-deposited films were found to be amorphous. The structural, chemical, and optical properties of the crystalline thin films with controlled phase formation were investigated after postdeposition annealing at various atmospheres and temperatures. Reducing and oxidizing atmospheres enabled the formation of pure VO2 and V2O5 phases, respectively. The possible band structures of the crystalline VO2 and V2O5 thin films were established. Furthermore, an electrochemical response and a voltage-induced insulator-to-metal transition in the vertical metal-vanadium oxide-metal device structure were observed for V2O5 and VO2 films, respectively.