COMBINED HREELS AND RAMAN-STUDY OF GAAS-ALAS SUPERLATTICES

GaAs-AlAs superlattices have been investigated by combining high-resolution electron-energy-loss spectroscopy (HREELS) and Raman spectroscopy. The superlattices were grown on GaAs(100) substrates by molecular-beam epitaxy. The sample surface was protected by an As capping layer formed in situ after growth, so that a well-ordered surface could be obtained by heating the sample mildly in UHV prior to HREELS measurements. The experimental results were compared with the dielectric theory of HREELS reported by Lambin et al. [Phys. Rev. B 32, 8203 (1985)]. The TO phonon frequencies and damping constants of GaAs and AlAs of individual samples, required for the theoretical calculations, were determined by Raman-scattering measurements. Excellent agreement was obtained between the theoretical and experimental results for all the samples with different layer thicknesses and for all the electron impact energies (from 4 to 35 eV) observed.