Dielectric and carrier transport properties of vanadium dioxide thin films across the phase transition utilizing gated capacitor devices

Abstract

Vanadium dioxide $({\text{VO}}_{2})$ is a strongly correlated oxide that undergoes a sharp metal-insulator transition (MIT) in the vicinity of room temperature. Fundamental knowledge of the semiconducting properties of thin film ${\text{VO}}_{2}$ is needed to advance our understanding of the microscopic transition mechanisms that are presently being actively explored and also for novel electron devices that could utilize the phase transition. In this report, the temperature dependence of the dielectric constant and carrier conduction in ${\text{VO}}_{2}$ thin films are investigated, from quantitative capacitance-voltage analyses of a multilayer capacitor with ${\text{HfO}}_{2}/{\text{VO}}_{2}/{\text{HfO}}_{2}/n\text{-Si}$-substrate stack structure. The finite conductance of the ${\text{VO}}_{2}$ in the capacitor structure is taken into account in the impedance transformations to obtain material properties as a function of temperature. The dielectric constant of ${\text{VO}}_{2}$ increases from a value of $\ensuremath{\sim}36$ at room temperature to a value exceeding $6\ifmmode\times\else\texttimes\fi{}{10}^{4}$ at $100\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. The carrier type of ${\text{VO}}_{2}$ thin film is electronic, determined by the polarity of the capacitance-voltage spectra. The electron carrier concentration of the ${\text{VO}}_{2}$ thin films shows about four orders of magnitude increase from room temperature to the temperature near phase transition. The approach of deriving insights into carrier conduction from capacitance measurement analyses can be applied to other materials beyond ${\text{VO}}_{2}$, wherein sensitive temperature-dependence or low carrier mobility makes Hall measurements challenging. Furthermore, the stack structure consisting of ${\text{HfO}}_{2}/{\text{VO}}_{2}/{\text{HfO}}_{2}/n\text{-Si}$ shows a strong temperature dependence of capacitance due to the MIT in the sandwiched ${\text{VO}}_{2}$ layer. This suggests the potential for strongly correlated oxides that undergo a hysteretic MIT in thermally tunable capacitors that could be of interest for solid-state devices.