Temperature dependence of a.c. conductivity of chalcogenide glasses

Abstract

A theory based on two electrons hopping between defect sites recently proposed (Elliott 1977, 1978) to account for the frequency dependence of the conductivity of chalcogenide glasses is analysed here with regard to the predicted temperature dependence. To a first approximation, the logarithm of the a.c. conductivity is predicted to be directly proportional to the temperature, a finding qualitatively borne out by experimental data. A detailed quantitative analysis is made on data taken by Rockstad (1972) on thin films of α-As₂Te₃. The present theory is obeyed excellently at low temperatures, and an estimate of 6 × 10^−-12 s is made for the. relaxation time involved. At higher temperatures a different mechanism is deduced to predominate; namely, that of quantum-mechanical tunnelling between localized states at the valence band edge. A value of 130 A for the spatial extent of the localized wavefunction is estimated for the energy at which tunnelling is believed to take place, namely some 0·03 eV from the mobility edge.