Dielectric Spectroscopy of VO₂:Ge Films

Abstract

The frequency dependencies of complex impedance $\dot {Z}$, dielectric permittivity ε, and dielectric loss tangent tanδ of thin (1400 Å ) films V_{1 –x}Ge_xO₂ (for x = 0 and 0.03) are studied in the frequency range of 10‒10⁶ Hz at 300 K. It is found that, at x = 0, the frequency dependence of tanδ 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 VO₂: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 VO₂ nanocrystallites in the V_0.97Ge_0.03O₂ film, including Ge-doped nanocrystallites and practically nondoped ones.