D.c. and a.c. electrical properties of vacuum evaporated thin SiO/GeO₂ films

Abstract

The d.c. and a.c. electrical properties were studied for various compositions of SiO/GeO₂ co-evaporated thin films carrying aluminium electrodes, in the temperature range 193–413 K. A.c. measurements were made over the frequency range 2x10²–10⁶Hz. The value of the d.c. activation energy was found to decrease with increasing GeO₂ content in the SiO. In the region of high applied field (above 10⁶ Vm⁻¹, the conduction mechanism is governed by Schottky emission at the blocking contact. The a.c. electrical conductivity, σ(ω), varies with frequency according to the relation σ(ω) ∝ ω^s, where the exponent s was found to be dependent on temperature and frequency. The a.c. conduction at low temperature was due to an electronic hopping process. The number of localized sites was estimated from the a.c. measurements for different compositions of SiO/GeO₂ using the models proposed by Elliott and by Pollak, and the values are compared. The Elliott model satisfactorily accounts for the observed a.c. electrical results. A correlation was found between activation energy, optical band gap, conductivity and number of localized sites for the various compositions of SiO/GeO₂ films. The relative dielectric constant, ɛ_r, and loss factor, tan δ, were found to increase with the increase of GeO₂ content in the films.