DISSIPATIVE ELECTRON-TUNNELING FROM SHALLOW DONORS IN GE

The effect of lattice vibrations on the held ionization dynamics of sh allow donors in pure germanium is investigated by transient tunnelling spectroscopy in the temperature range from 4.2-6.5K. In this range th e excited donor levels are populated and the free electron concentrati on in the conduction band is negligible. The increase of the tunnellin g rate, when the lattice temperature is raised, is observed. The exper imental results are explained by acoustic phonon assisted and activate d tunnelling mechanisms. Both mechanisms are shown to enhance the tunn elling rate. The importance of excited donor states in the dissipative tunnelling is stressed.