The transport properties of boron-doped amorphous silicon and their interpretation

Abstract

Thermoelectric power and conductivity measurements were made on a series of a-Si specimens doped with varying amounts of boron. The samples were prepared by the glow-discharge decomposition of silane containing predetermined concentrations of diborane. The results have been interpreted in terms of two different models. First, a two-conduction-path model was used, with transport at higher temperatures taking place in the extended hole states and at lower temeratures by hopping through the tail states. All parameters deduced on the basis of this model formed a consistent pattern throughout the doping range, and the detailed behaviour of σ (T), S(T) and Q(T) could be fitted remarkably well in terms of the model parameters. Secondly, the potential fluctuation model, proposed by Overhof and Beyer (1981), was used in the interpretation of the data, leading to reasonable agreement between theory and experiment, although basic inconsistencies did arise in the detailed analysis. It is concluded that in general both mechanisms are relevant to the description of the transport properties; however, for the B-doped specimens investigated, which possess a low level of potential fluctuations, the two-path model provides the more consistent interpretation.