DIELECTRIC SUSCEPTIBILITY MODEL FOR OPTICAL PHONONS IN SUPERLATTICES

The form of the long-wavelength optic-phonon modes in semiconductor su perlattices is described using a dielectric susceptibility model. This model only requires knowledge of the frequencies and eigenvalues for LO and TO modes propagating along the superlattice growth direction z. From these, the principal-axis dielectric susceptibilities epsilon(zz )(omega) and epsilon(xx)(omega) can be obtained, and so a full descrip tion of the optic phonons is possible for any phonon propagation direc tion. Calculations of confined LO and TO mode frequencies and displace ments are made for GaAs/AlAs superlattices. The susceptibilities and m ode displacements are compared using a simple continuum model and a mi croscopic linear-chain model. The susceptibilities are also used to mo del nonresonant Raman-scattering spectra, and are shown to give result s that are in close agreement with published micro-Raman measurements. [S0163-1829(98)02007-4].