UNIFIED TREATMENT OF TEMPERATURE, CONCENTRATION, AND ELECTRIC-FIELD DEPENDENCES OF VARIABLE-RANGE-HOPPING CONDUCTIVITY

The conductivity of Ge1-xAux thin films was studied at temperatures in the range 0.019<T<4.2 K. In the linear (low-bias) regime, samples with 0<x<0.14 showed resistivity with exp T*/T behavior. The x dependence of T* accurately followed the theory of Shklovskii and Efros, which includes a Coulomb gap in the electronic density of states. At bias fields exceeding 104 V/m, nonlinearity was observed that can be accounted for by introducing the effect of the bias field into a calculation of the optimized hopping exponent. © 1995 The American Physical Society.