Lattice dynamics and Raman scattering by phonons of GaAs/AlAs(001) superlattices

The lattice dynamics of (GaAs)(n)/(AlAs)(n)(001) superlattices (SLs), n = 1,2, with perfect and disordered (non-perfect) interfaces is studied in detail. The SLs with disordered interfaces are approached by primitive cells, much larger in volume than that of the perfect SL primitive cell. The dynamical matrices of the SLs have been constructed from a combination of the dynamical matrices corresponding to the bulk crystalline constituents, while the interionic forces are calculated by using a ten-parameter valence overlap shell model (VOSM). Furthermore, we calculate the Raman spectra, for both perfect and disordered superlattices by using an eight-parameter bond polarizability model (BPM). Our theoretical results are in very good agreement with the available experimental spectra. Finally, our results clearly demonstrate that intermixing of Ga and Al cations, even to a very small extent, can induce Raman activity, which although not expected in the spectra of perfect superlattices, is actually observed experimentally.