Dielectric spectroscopy of VO$_{2}$:Ge films

The frequency dependencies of complex impedance $\dot {Z}$, dielectric permittivity $\dot\varepsilon$, and dielectric loss tangent tan$\delta$ of thin (1400 $\mathring{\mathrm{A}}$) films V$_{1-x}$Ge$_{x}$O$_{2}$ (for $x$ = 0 and 0.03) are studied in the frequency range of 10–10$^{6}$ Hz at 300 K. It is found that, at $x$ = 0, the frequency dependence of tan$\delta$ has a maximum at a frequency of 100 kHz, whereas at $x$ = 0.03 an additional maximum in the region of 10 kHz is detected. Also, the Cole–Cole diagram of VO$_{2}$:Ge films acquires a feature in the form of an additional semicircle. Owing to the extremely high sensitivity of the dielectric spectroscopy method, the proposed equivalent circuit diagram of the sample allowed detecting the existence of two sets of VO$_{2}$ nanocrystallites in the V$_{0.97}$Ge$_{0.03}$O$_{2}$ film, including Ge-doped nanocrystallites and practically nondoped ones.