Pressure dependence of hopping conduction in amorphous Ge alloys

The ac-conductivity of amorphous Ge-Au alloy has been measured at frequencies of 20 Hz to 1 MHz, at pressures up to 5 GPa and temperatures down to 77 K using a Drickamer-type high pressure cell. The ac-conductivity increases with increasing frequency. With increasing temperature, the rising frequency increases. From these results, temperature dependence of conductivity was obtained without shape parameters of the sample. The temperature dependence of hopping conductivity is found to be well described by a power law expected from the Multiphonon Process model. The exponent n in the power law increases with increasing pressure below 2 GPa, and decreases above 2 GPa. This pressure dependence of n agrees with the previous reported results from dc electrical resistivity measurements. The anomalous pressure dependence of n is discussed in relation to the Debye frequency, atomic distance, void size, and the density of states at the Fermi level.