Transport properties of a-Si: H alloys prepared by r.f. sputtering

Conductivity and thermopower measurements as a function of temperature are reported for a series of r.f. sputtered hydrogenated a-Si samples doped with P. The results are analysed, along with others in the literature, in terms of several models for transport. It is concluded that the best overall fit to the data involves conduction in an intrinsic band above about 400 K and conduction in a P-related impurity band between about 200–400 K. The proposed transport in the latter temperature regime disagrees with earlier conclusions of Spear and Le Comber, and it also implies a smaller shift of the Fermi level with doping than does their model. The implications of this interpretation for current measurement of Hall effect and drift mobility are briefly outlined, as are difficulties in the detailed interpretation and complications related to heterogeneity in structure.