Dielectric spectroscopy as a method for testing thin vanadium dioxide films

We have analyzed the dielectric spectra of thin (1200 $\mathring{\mathrm{A}}$) films of vanadium dioxide, a material with strong electron–electron correlations. We have tested both undoped and germanium-doped VO$_2$ : Ge films. The latter exhibits an additional peak in the frequency spectrum of the tangent of the dielectric loss angle. We have analyzed the fine structure of the spectra and provided physical interpretation of two peaks on the frequency dependence of the tangent of dielectric loss angle and two semi-circles on the Cole–Cole diagram. Analysis of results has been performed based on equivalent electric circuit diagrams of samples, viz., one-loop RC circuit for the undoped VO$_2$ film and two-loop circuit for VO$_2$ : Ge film. The numerical values of parameters of model systems have been determined.