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

Vanadium dioxide (VO2) 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 VO2 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 VO2 thin films are investigated, from quantitative capacitance-voltage analyses of a multilayer capacitor with HfO2/VO2/HfO2/n-Si-substrate stack structure. The finite conductance of the VO2 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 VO2 increases from a value of similar to 36 at room temperature to a value exceeding 6 x 104 at 100 degrees C. The carrier type of VO2 thin film is electronic, determined by the polarity of the capacitance-voltage spectra. The electron carrier concentration of the VO2 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 VO2, wherein sensitive temperature-dependence or low carrier mobility makes Hall measurements challenging. Furthermore, the stack structure consisting of HfO2/VO2/HfO2/n-Si shows a strong temperature dependence of capacitance due to the MIT in the sandwiched VO2 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.