ANGULAR-DISPERSION OF CONFINED OPTICAL PHONONS IN GGAS/ALAS SUPERLATTICES STUDIED BY MICRO-RAMAN SPECTROSCOPY

Microscopic Raman measurement of the GaAs-like optical phonons of (001)-(GaAS)(8)/(AlAs)(8) and -(GaAs)(12)/(AlAs)(12) superlattices are presented. The phonon dispersion with respect to the angle 8 between growth axis of the superlattice and the phonon wavevector is investigated over the whole range from 0 degrees to 90 degrees by scattering from surfaces which were polished under various angles. It is found that the frequencies of confined modes with even symmetry remain constant, whereas the modes with odd symmetry are shifted downwards in frequency with increasing Theta. Frequency gaps in the angular dispersion due to mode anti-crossing are observed. The experimental data are in reasonable agreement with calculations performed within a recently developed continuum model based on linear combinations of LO, TO and interface modes.