dc Conductivity of Amorphous Germanium and the Structure of the Pseudogap

This work centers on the now disputed interpretation of the observed $T^{-\frac{1}{4}}$ dependence of the conductivity in amorphous group-IV semiconductors by hopping near the Fermi energy. We find the arguments against this interpretation inapplicable. We present experimental results of the temperature dependence of the resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ of gas-free and void-free amorphous germanium, as well as theoretical results of $\rho \mathrm{}\left(T\right)\mathrm{}$ for a hopping model with a band of localized states near the Fermi energy. The agreement is good and leads to the estimate of the bandwidth of 0.3 eV.