CONFINED LO PHONONS IN GAAS/ALAS SUPERLATTICES

We report the observation of both GaAs and AlAs confined LO phonons in short-period GaAs/AlAs superlattices. The measured GaAs mode frequencies are found to map well onto the bulk dispersion curve with a suitable choice of an effective wave vector, confirming the validity of this technique for determining bulk phonon dispersions over at least the first half of the bulk Brillouin zone. The frequency separation of confined AlAs LO modes is found to be consistent with a weak dispersion of this branch along the [001] direction, in agreement with recent lattice-dynamic calculations.