Unveiling the Role of VO2 (B) Polymorph in the Insulator–Metal Transition of VO2 (M1) Thin Films

Abstract

Characteristic first‐order insulator–metal transition (IMT) in VO2 (M1) phase finds a place in ample practical applications such as switches, transistors, memory devices, and energy‐saving windows. A polymorph VO2 (B) phase which may appear as an additional phase can strongly influence IMT in VO2 (M1) and not much is known about it. Here, the electrical conductivity and the electronic structure studies on the VO2 thin films on R‐ and C‐cut sapphire and silicon (Si) substrates are reported. X‐ray diffraction (XRD) and Raman spectra confirm the growth of VO2 (B) as well as VO2 (M1) polymorphs on the sapphire substrates and the pure VO2 (M1) phase on the Si substrate. The first‐order IMT is observed in all the thin films, however, due to the presence of the semimetallic VO2 (B) phase in the thin film on sapphire substrate, a decrease in the IMT strength and higher electrical conductivity have been observed. The electronic structure studies, by utilizing soft X‐ray absorption spectroscopy (SXAS) measurements, reveal that the presence of VO2 (B) phase not only causes an overall increase in the crystal field energy but also significantly affects the orbital occupancies around the Fermi level.