Lattice properties of strained GaAs, Si, and Ge using a modified bond-charge model.

A phenomenological lattice dynamics model based on the bond-charge model has been developed that describes how strain affects phonon frequencies and elastic constants in groups IV ~homopolar! and III-V ~heteropolar! semiconductor thin films and strained layers. A quasiharmonic approach is adopted, using force constants that depend linearly on strain. This model uses available experimental data and can predict the effect of arbitrary strains on nonpolar and polar semiconductor films. Using this model, the phonon dispersion relations are obtained for bulk and strained-layer heterostructures of Ge and GaAs on Si, and the mode Grüneisen parameters and the pressure dependence of second-order elastic constants are determined for bulk Si, Ge, and GaAs. Also, it is shown that analyzing the effect of strains on semiconductors leads to a better and more physical set of force constants for the bond-charge model for unstrained materials.