Electrical Properties of Amorphous Se, ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$, and ${\mathrm{As}}_2$ ${\mathrm{S}}_3$

The room-temperature ac conductivity and the real part of the dielectric constant of amorphous Se, ${\mathrm{As}}_2$ ${\mathrm{Se}}_3$, and ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ have been measured in the 1.0 × ${10}^2$ - 3.6 × ${10}^{10}$-Hz frequency range. In addition, the temperature dependence of the low-frequency dielectric constant and the ac conductivity of Se were also measured in the 320 - 77 °K range. For all three materials the dielectric constant shows less than 15% dispersion in the entire frequency range, while the ac conductivity is proportional to ${\omega }^n$ with $n=0.\mathrm{}95\pm 0.05$ in the 1.0 × ${10}^2$ - 5.0 × ${10}^7$-Hz frequency range. The results indicate that the frequency dependence of the ac conductivity may saturate below ${10}^{10}$ Hz. Consideration of different models for the frequency-dependent conductivity leads to thermally activated hopping as the most likely process. The density of the localized states participating in this process is not described adequately, however, by any of the existing theoretical treatments of amorphous materials. It is suggested that the effect of impurities and defects should be considered in detail.