Lattice dynamics of thin ionic slabs. III. Application to GaAs slabs

The lattice vibrations of thin slabs (up to 25 layers) of GaAs are calculated for zero wave vector, on the basis of a rigid-ion model fitted on the phonon dispersion curves of the infinite crystal. It is shown that all the modes, except the surface ones, fall on the branches of the dispersion curves of the infinite crystal, while the surface modes seem to be combinations of those missing near the zone-edge modes. Comparison is made with former calculations and the influence of the short-range interaction near the surfaces and that of possible macroscopic fields is discussed.