Heteroepitaxial Growth and Phase Transition Properties of Vanadium Dioxide Thin Films

Vanadium dioxide thin films were deposited on R(012) and C(001) planes of sapphire and titanium dioxide substrates using pulsed laser deposition. Growth conditions were optimized to obtain epitaxial growth of films up to 100 nm thick. As is typical for oxide thin films, oxygen pressure and temperature are the main parameters governing the formation of the well-known VO$_{2}$ phase that exhibits the semiconductor-to-metal transition near 68$^{\circ}$C. A systematic study of the optical transmission and reflection in the near-infrared was done as a function of temperature between 20$^{\circ}$C and 90$^{\circ}$C. The samples were analyzed by X-ray diffraction, ion-beam channeling and scanning electron microscopy in order to determine epitaxy and crystal quality. The results show that the growth of VO$_{2}$ has strong substrate dependence. Tungsten doping of the epitaxial VO$_{2}$ films was also carried out in order to lower the phase transition temperature and lattice locations of the dopant atoms were determined.