Electric transport mechanism in intrinsic and p-doped microcrystalline silicon thin films

Abstract

Intrinsic microcrystalline silicon thin films, as well as p-type doped with boron prepared by very high-frequency plasma enhanced chemical vapor deposition, have been studied. Raman spectroscopy, atomic-force microscopy, lateral dark conductivity, and ultraviolet-visible transmittance were used to characterize each sample. Conductivity of all samples, as a function of the inverse of temperature, showed a thermally activated behavior of electric carriers with temperature-independent activation energy in all of the temperature ranges studied. Following the method proposed by Godet [C. Godet, J. Non-Cryst. Solids 299, 333 (2002)], assuming an exponential density of states for this group of different films, variable range hopping between defects near the Fermi level was established as a predominant electronic transport mechanism. Using classical equations of percolation theory, as well as the correlation found by Godet, the density of states near the Fermi level was calculated and found to give values that are consistent with the results of other independent experiments.