Film thickness dependence of electrical hysteresis and Hall effect of thermochromic VO2 thin films

Abstract

Vanadium dioxide (VO2) is a very well-known thermochromic material exhibiting a very effective first order semiconductor to metal (SMT) transition at a temperature of around 68°C. In this work we have investigated the thermochromic properties of VO2 thin films as a function of film thickness. The VO2 films were deposited by a two-step method on glass substrates. The changes occurring around the SMT have been systematically characterized by structural, optical, electrical, magnetic studies and their hysteresis cycles. The correlation between film thickness and transition temperature has been established for the VO2 films from the resistance variation during the heating and cooling cycles. The Hall voltage variation as a function of magnetic field has been measured for each of the VO2 film thicknesses. These Hall voltage measurements have enabled us to calculate the free electron density above and below the transition temperature for each of the VO2 samples. The free electron density changes conform to the semiconductor to metal transition observed and to the values mentioned in the literature.