(Invited) Semiconductor-to-Metal Transition in Atomic Layer Deposition (ALD) of VO₂ Films Using VCl₄ and Water

Abstract

Atomic layer deposition is used to synthesize 33 nm thick VO2 films using a vanadiumtetrachloride and H2O. The as-deposited VO2 films are amorphous and convert to the monoclinicphase after a post-deposition anneal ≥ 500 °C, 60-minute in forming gas. X-ray photoelectronspectroscopy suggests the annealed film is stoichiometrically VO2. Temperature-dependentRaman spectroscopy and ellipsometric studies reveal the semiconducting to metallic transition ofannealed and crystallized VO2 thin film. The phase transition temperature is recorded at 68 °C.Refractive index and extinction coefficient from ellipsometry confirm that beyond 68 °C, freecarriers are generated in the film. Electrical measurements performed on a fabricatedp++Si/VO2/Ti/Au device show semiconducting to metallic transition behavior at 68 °C with a high(semiconducting): low (metallic) resistance ratio of 66. A halide based atomic layer depositionchemistry provides a clean and robust approach to synthesizing high-quality VO2 films.