Transport in lithium-doped amorphous siliconf

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Abstract
Conductivity (σ) and thermopower (S) data are presented for an amorphous Si film prepared by the glow-discharge technique and doped step-by-step by implantation of 20 keV Li ions. The results are similar to those obtained by doping with phosphorus from the gas phase. By an analysis of In σ+ [eS/k] it is shown that for all doping steps the transport mechanism does not change with temperature. Thus, there is no indication of two-channel transport via localized and extended states. The mobility is found to be activated with an activation energy varying from 0.1 to 0.2 eV depending on the doping rate, while the prefactor of the conductivity is rather insensitive to doping. It is shown that the statistical shift of the Fermi level must be quite large at medium and high doping levels in order to account for the experimental data.