Lattice Dynamics and the Optical Properties of Semiconductors: Theory of the Temperature Dependent Dielectric Functions of GaAs and Si and Comparison with Experiment

A novel method for calculating the temperature dependencies of the linear dielectric functions of semiconductors is described, in which the lattice vibrations are represented by thermally-perturbed atomic configurations extracted from molecular dynamics (MD) simulations. Our theoretical results for bulk GaAs and Si in the range from 0 to 930 K are in good overall agreement with highly accurate ellipsometric measurements. The implementation of the method resolves a serious discrepancy in energy and line shape between experiment and the latest optical models, all of which neglect lattice dynamics and provide information on the indirect optical transitions and indirect gap in Si.