ATOMIC VIBRATIONS IN THIN [111](GAAS)N(ALAS)(N) SUPERLATTICES

We present theoretical investigations of atomic vibrations in thin (Ga As)(n)(AlAs)(n) superlattices grown in the [111] direction with f.c.c. stacking, using the adiabatic bond-charge model. In the acoustic rang e we confirm the existence of guided Love modes. In the optical range we observe folding, confinement and mode anisotropy behaviours. We sho w that confined optical modes approximate travelling waves in the prop agation layer, decaying rapidly outside. In addition we clearly show o ptical interface modes of both 'AlAs' and 'GaAs' type, and that these modes are of the 'Fuchs-Kliewer' variety. We compare the results obtai ned for the [111] direction to previous results obtained for the [001] and [110] directions.