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

Abstract

Atomic layer deposition was adopted to deposit VO_x 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 VO_x. 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.