Deconvolution of activated and variable-range-hopping conduction for barely insulating arsenic-doped silicon

An explanation, using the logarithmic derivative method, is given for some previously unexplained features of the temperature dependence of the conductivity for barely insulating Si:As for 10 K< T< 78 K. The results and analysis suggest an important high-temperature correction to the prefactor of Mott variable range hopping, and also give more reliable values of the activation energy and the temperature-dependent prefactors of the activated conduction. The two samples closest to n(c) provide evidence for temperature-dependent activation energies. The activated contribution allows the determination of the mobility mu(n,T) for itinerant electrons above the mobility edge. This mobility is consistent with ionized impurity scattering in the impurity band. The logarithmic derivative method also provides a method for determining the fraction f(a)(n,T) of donor electrons thermally excited above the mobility edge. The activated conductivity results are compared with Manfield's expression for impurity scattering as adapted to the impurity band case. [S0163-1829(99)06039-7].