CONTRIBUTION OF SINGLE POLARON HOPPING TO AC CONDUCTION IN AMORPHOUS CHALCOGENIDES

Abstract
Although it is now fairly well established that defects in amorphous chalcogenide semiconductors are normally charged (D⁺ and D^-), it is proposed that neutral defects D⁰ (generated by the reverse reaction of 2D⁰ → D⁺ + D^-) can be important for a.c. conductivity. It is shown that the contribution to σ(ω,T) from correlated barrier hopping of single polarons exceeds that of bipolarons at high temperatures (T) and/or low frequencies (ω). An expression for σ(ω,T), which includes terms due to electrons hopping between D⁰ and D⁺ and holes between D⁰ and D^-, as well as two electrons hopping between D^- and D⁺ (bipolarons), is able to account for all the features observed in many materials. The energy levels and densities of the defect states for Se, two Se-Te alloys, As₂Te₃ and As₂Se₃ are deduced from a comparison of the theory with experimental data.