On the validity of the relaxation time approximation for silicon in the region of irreversible thermodynamics

The authors discuss the modelling of macroscopic balance equations in irreversible thermodynamics as resulting from stationary Monte Carlo bulk simulations for electrons. The Onsager coefficients related to these equations are determined from time integrals of fundamental microscopic correlation functions. Special interest is given to the validity of the relaxation time approximation and the Wiedemann-Franz law. The simulation results for silicon clearly show that a high doping level (>1018 cm-3) is a sufficient condition for the validity of both approximations in inhomogeneous systems.