Variable-range hopping, as evidenced by a resistivity proportional to exp($T^{\mathrm{-}1/4}$), has been induced in many III-V amorphous semiconductors (InSb, AlSb, and GaAs) and even in chalcogenide glasses (${\mathrm{As}}_2$${\mathrm{Te}}_3$, ${\mathrm{As}}_2$${\mathrm{Te}}_{3\mathrm{-}\mathrm{x}}$${\mathrm{Se}}_{\mathrm{x}}$, and GeTe) by depositing films at 77 K. It is therefore remarkable that the same procedure failed to generate variable-range hopping in GaSb, which is one of the less ionic III-V semiconductors. Besides differences in the dc conductivity, there are also different behaviors in the ac conductivity of amorphous semiconductors. The low-temperature ac conductivity of all amorphous semiconductors is proportional to ${\omega }^s$$T^n$ with s≃1 and n<1, which is consistent with a model of correlated barrier hopping of electron pairs between paired and random defects. However, in the case of a-${\mathrm{SiO}}_2$ and a-${\mathrm{GeSe}}_2$ one finds, in addition, that the capacitance obeys the scaling relation C=A ln(T${\omega }^{\mathrm{-}1}$), which would suggest a conduction mechanism by tunneling relaxation. Furthermore, this scaling relation cannot be fitted to the data for a-${\mathrm{As}}_2$${\mathrm{Te}}_3$, a-InSb, and a-GaSb although the functional dependence of C on T and ω are similar.

• Received 7 May 1984

DOI:https://doi.org/10.1103/PhysRevB.31.2133