Hopping mechanism of electric transport in intrinsic and p-doped nanocrystalline silicon thin films

The effect of temperature and applied electric field on transport properties of intrinsic nanocrystalline silicon thin films as well as p type doped with boron prepared by VH-PECVD have been studied. The conductivity of all samples, as a function of the exponential of T-1/4 measured at intermediate fields, presented a linear behavior in all the temperature ranges studied (270-450 K). Following the method proposed by Godet [C. Godet, J. Non-Cryst. Solids 299-302 (2002) 333], a linear relationship between the conductivity prefactor (sigma(00)) and the characteristic temperature (T-0) of Mott's law was obtained for a group of quite different materials. From this, and using classical equations of Percolation Theory, the density of states near the Fermi level, the range of hopping, the activation energy for hopping, and the localization parameter were calculated. At low applied fields, dark conductivity becomes field dependent. The non-ohmic behavior of the conductivity observed is analyzed in terms of the hopping transport equations. (C) 2004 Elsevier B.V. All rights reserved.