We present a new interpretation of the anisotropy of the conductivity in thin films of amorphous Ge and Si. The interpretation is based on a transition from percolation conduction to Miller and Abrahams's conduction at small film thickness. A simple theory, together with experimental data, is presented. The comparison between them is found to be good.

• Received 16 August 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.1304