Frequency-dependent loss in sputtered amorphous germanium films Measurements at low temperatures

Abstract
Measurements of frequency-dependent loss in thin films of amorphous germanium prepared by r.f. sputtering are reported. The loss characteristics can be divided into two temperature regimes. At high temperatures electron tunnelling between defects is observed, which in the high-temperature limit becomes non-dispersive. At low temperatures, below 15 K in pure films, the loss becomes less dependent on temperature and shows a strong dependence on the exciting a.c. field. In this regime the most likely mechanism is of electron polarization within defects around 1 nm in extent.