Localized conduction processes in amorphous germanium

The current-voltage behaviour of amorphous germanium sandwich layers has been investigated in the temperature range 2°K to 79°K. The results obtained, in conjunction with those of Walley (1968) for the range 77°K to 300°K, are discussed in terms of a model for conduction in amorphous germanium. It is also shown that similar processes must be responsible for conduction in amorphous silicon.Following the analyses of Mott (1969) and Hill (1970) it is concluded that conduction in amorphous germanium (and silicon) is by hopping in the temperature range up to 300°K. The carriers are supplied by a large density of acceptor states (1018-1019 cm-3) near to the localized valence band. At low temperatures the current limiting process is field assisted emission from acceptors and this gives rise to power law (I ∝ V8) and exponential (I ∝ exp V½) behaviour in the current-voltage characteristics. Transport between the acceptors is via states in the localized part of the valence band. At higher temperatures the limiting process is transfer between the localized states rather than thermal emission from the ionizable centres, and the T-¼ proposed by Mott (1969) for hopping is observed.