Confinement of optical phonon modes in thin (GaAs) n(AlAs) n superlattices

Abstract

We present theoretical investigations of atomic vibrations in thin (GaAs) n (AlAs) n superlattices grown along the symmetry directions [0 0 1], [1 1 0] and [1 1 1] using the adiabatic bond charge model. We find that optical phonon modes get quantized for all layer thicknesses, including the monolayer case. In particular, we show that the energy gap between the primary and secondary quantized longitudinally optic modes is dependent upon the direction of growth in addition to the period of thickness of the superlattice. We show that the direction dependence is due to the polarity of the system. We also calculate the unfolding behaviour of the quantized superlattice frequencies and provide a comparison with experimental Raman peaks.