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 VO x thin films using vanadyl tri-isopropoxide {VO[O(C 3 H 7 )] 3, VTIP} and water (H 2 O) 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 VO 2 and V 2 O 5 phases, respectively. The possible band structures of the crystalline VO 2 and V 2 O 5 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 V 2 O 5 and VO 2 films, respectively.