Mott transition and Schottky barrier observation by photocurrent measurement in VO$_{2}$ devices

As one of the metal-insulator transition (MIT) mechanism, the Mott transition occurs due to Coulomb interactions of electrons in VO$_{2}$. This suggests that VO$_{2}$ does not undergo the structural phase transition (SPT) when MIT occurs. For observing the Mott transition and Schottky barrier in VO$_{2}$ devices, we simultaneously observe the temperature dependence of photocurrent and local structural observation in the two-terminal VO$_{2}$ devices by using scanning photocurrent microscopy, which is a typical method for showing images of nanometer-length scale and Raman spectroscopy, respectively. In particular, the photocurrent between two electrodes through VO$_{2}$ channel increases due to the variation of schottky barrier height. Furthermore, the work functions of VO$_{2}$ thin film is investigated while varying the device temperature, which could assure the Schottky contact formation. We also find the metallic phase with monoclinic structure below a conventional transition temperature of VO$_{2}$ ($\sim$ 68 $^{\circ}$C), indicating the Mott transition of VO$_{2}$.