Abstract
A.c. and d.c. conductivities of amorphous films of Ge—Sb–Se have been investigated for different Sb: Se ratios, keeping the Ge content constant at 20 at. %. The a.c. conductivity [sgrave](ω, T) in the frequency range 0•5-10•0 kHz is found to obey the law [sgrave](ω, T) = Aω3. The exponent s is found to decrease with increasing temperature and Sb content, which is inconsistent with the quantum-mechanical tunnelling model. A strong temperature dependence of the a.c. conductivity [sgrave](ω, T) and exponent s in the entire range of temperatures and frequencies is reasonably interpreted by the correlated barrier hopping model, taking into account the contribution of both single polarons and bipolarons. The values of the energy of bound states, the correlation energy and the Fermi energy are estimated from the best fit between theoretical and experimental results. It is observed that the correlation energy increases while the energy of bound states decreases with increasing Sb content. The decrease in energy of bound states can be understood in terms of the decrease in the band gap of the material with the increasing Sb content.