CONDUCTIVITY OF WEAKLY INSULATING AMORPHOUS NICKEL-SILICON FILMS BELOW THE METAL-INSULATOR-TRANSITION

The electronic conductivity has been measured in homogeneous, weakly i nsulating, amorphous nickel-silicon films located just below the metal -insulator transition (MIT). The conductivity follows a simple CTz pow er-law dependence with z approximate to 1/2 over a large temperature i nterval. In contrast, a Mott variable-range hopping expression could n ot be fitted successfully through these zero-field conductivity data. The CTz behaviour can be explained using the three-dimensional (3D) el ectron-electron interaction (EEI) theory. The negative magnetoconducta nce data observed in these weakly insulating films can be fitted nicel y using only the 3D EEI theory. A crossover of the conductivity from t he simply power-law CTz dependence at high temperatures to an activate d hopping-law dependence in the liquid helium temperature region is ob served; this transition is attributed to changes in the energy depende nce of the density of states near the Fermi level. The conductivity of these weakly insulating films can be fitted well over three decades o f temperature using an empirical scaling expression suggested by Mobiu s et al.