A.c. conductivity of amorphous germanium by time-domain spectroscopy

A new experimental technique, time domain spectroscopy (TDS) which enables the dielectric properties of materials to be measured over a wide range of frequencies is described. Results are presented of such measurements on amorphous germanium, prepared by thin film evaporation. The d.c. conductivity is shown to obey Mott's variable range hopping formula, whilst the a.c. conductivity has a frequency dependence of the form σ(ω)∝ω8, where 0.7 <s < 1.6. A model is proposed which demonstrates the possibility of a super-linear frequency dependence of a.c. conductivity in an inhomogeneous system.