A lattice-dynamics model for the mixing of acoustic and optical modes in III-V compounds and its effect on the electron-phonon interaction

Abstract

This paper addresses the phenomenon of mode-mixing in the acoustic and optical branches of the vibrational modes of III-V compounds, and its effect on the electron-phonon interaction. A description is given based on the analytic lattice-dynamics model of long wavelengths in the diamond lattice based on valency force fields (VFF). This model is known to give good results for the acoustic elastic constants, and it allows an account to be given of optical-mode elasticity. This versatility motivates the presentation in full given here. Its application to optical polar material introduces effects associated with the difference of atomic masses and differences of valence bonding, both of which are the source of the mixing of acoustic and optical modes towards short wavelengths. Short wavelengths are associated with confinement in nanostructures. It is shown that the electron-phonon interaction at extremely short wavelengths may become non-polar in both branches, but the effect of this is likely to be small. A more definitive conclusion awaits the extension of the VFF model to short wavelengths.