Semiconductor-insulator transition in VO2 (B) thin films grown by pulsed laser deposition

Thin films of B-phase VO2 were grown by pulsed-laser deposition on glass and (100)-cut MgO substrates in a temperature range from 375 to 425 degrees C and at higher gas pressures than usual for this technique. The films were strongly oriented, with ab-planes parallel to the substrate surface. Detailed study of surface morphology through Atomic Force Microscopy images suggest significant differences in evolution as a function of growth temperature for films on the two types of substrates. Measurements of electrical conductivities through cooling-heating cycles from room temperature to 120K showed changes of five orders of magnitude, with steeper changes between room temperature and similar to 150 K, which corresponds with the extended and reversible phase transition known to occur for this material. At lower temperatures conductivities exhibited Arrhenius behavior, indicating that no further structural change was occurring and that conduction is thermally activated. In this lower temperature range, conductivity of the samples can be described by the near-neighbor hopping model. No hysteresis was found between the cooling and heating braches of the cycles, which is at variance with previous results published for VO2 (B). This apparent lack of hysteresis for thin films grown in the manner described and the large conductivity variation as a function of temperature observed for the samples suggests this material could be of interest for infrared sensing applications. (C) 2015 AIP Publishing LLC.