Correlation between thermal hysteresis width and broadening of metal-insulator transition in Cr- and Nb-doped VO2 films

We investigated the effects of Cr and Nb doping on the metal insulator transition (MIT) of single-oriented VO2 films deposited on Al2O3 substrates. The MIT temperature (T-MI) increased with trivalent Cr doping, whereas it decreased with pentavalent Nb doping. The temperature coefficient of resistance (TCR) and the thermal hysteresis width of the MIT (Delta T-MI) were suppressed by Cr and Nb doping, and Nb doping was about twice as effective as Cr doping for decreasing TCR and Delta T-MI. We found that the maximum TCR and Delta T-MI for the doped VO2 films have a correlation with the lattice constant irrespective of doping elements, suggesting that the lattice deformation caused by metal-ion doping is involved in the decreases in TCR and Delta T-MI. There is also an apparent correlation between the maximum TCR and Delta T-MI for the doped VO2 films. The present findings suggest that the combination of metal-ion doping with other techniques such as strain control is required to achieve nonhysteretic MIT with a large TCR in VO2 films. (C) 2014 The Japan Society of Applied Physics