Localized gap states in amorphous semiconductors estimated by dielectric relaxation

Low-frequency dielectric relaxation of amorphous ${\mathrm{Te}}_x{\mathrm{Se}}_{1-x}$ and ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$ has been measured. Dielectric dispersion was found in $\omega \simeq 0.1-500$ Hz for ${\mathrm{Te}}_x{\mathrm{Se}}_{1-x}$ and $\omega \simeq 0.1$ Hz for ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$ at 293 K, where $\omega$ is the angular frequency. The activation energies for dispersion were smaller than that for electrical conduction in contrast with oxide glasses. To account for the data, a model is proposed. The dielectric loss is caused by hopping of trapped holes between localized centers through tail states. From this model the hole-trap levels and its density are estimated. It is suggested that measurements of low-frequency dielectric relaxation find broad application in the estimation of deep localized states in amorphous semiconductors.