Time-of-flight (TOF) and charge collection measurements are evaluated to determine electron transport quality of a-Si1−x Gex:H for 0 ≤ x ≤ 0.3. The drift mobility data are used to calculate the tail state distribution at the conduction band, which turns out to be of hybrid structure (flat linear followed by a steep exponential decay). By incorporation of Ge additional localization introduced by chemical disorder broadens the band tail. The dangling bond density, calculated from electron µDTE products, also dramatically increases. Both effects contribute to the drop of photoelectronic quality of a-Si1−xGex: H alloys.
In addition it is shown that the extended state mobility deduced from TOF experiments reflects a tunneling transport mechanism in localized states above a dominant transport level that separates states with high tunnel probability from states where carriers propagate via thermal release from and capture into localized states.