1Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock, Texas 79409-3102, USA
2Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China
3Department of Physics and MSEC, Texas State University, San Marcos, Texas 78666, USA
2Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China
3Department of Physics and MSEC, Texas State University, San Marcos, Texas 78666, USA
Results are reported on tuning the electrical and optical properties of sputter-deposited vanadium dioxide (VO2) thin films through control of substrate growth temperature (Ts). As Ts increases from 550 to 700 °C, the morphology changes from granular to smooth film and finally to rough film. X-ray diffraction shows the presence of VO2 along with additional weak features related to the presence of non-stoichiometric phases. Electrical measurements show the phase transition to change from abrupt to gradual as both the below- and above-transition resistivities vary with Ts. The transition and hysteresis dependences observed in electrical resistivity are similarly observed in infrared transmission. Terahertz transmission measurements show that high conductivity above the phase transition is more important in achieving high modulation depth than obtaining high resistivity below the transition. We attribute changes in the electrical and optical properties to the formation of V and O vacancies, which result in diverse valence states from the ideal V4+ of VO2. Low Tsproduces material with V5+ states resulting in higher resistivity in both the insulating and metallic phases. Alternatively, high Ts introduces material with V3+ states leading to lower resistivity in the insulating phase but slightly higher resistivity in the metallic phase.
