Dielectric spectroscopy and semiconductor-metal phase transition in VO 2 :W films

The frequency dependencies of complex dielectric permittivity ε, and dielectric loss tangent tgδ of thin (1400 Å) films VO2:W are studied in the frequency range of 10-1-106 Hz at 300 K. It is found that, for undoped VO2 the frequency dependence of tgo has a two maximums at a frequency of 1 kHz and 0,1 Hz, whereas for VO2:W an additional maximum in the region of 100 kHz is detected. Also, the Cole–Cole diagram of VO2:W films acquires a feature in the form of an additional semicircle. The proposed equivalent circuit diagram of the sample allowed detecting the existence of three sets of VO2 nanocrystallites in the VO2:W film, including W-doped nanocrystallites and two practically nondoped ones. The mechanism of the effect of doping with tungsten on the metal-insulator phase transition is proposed.