Abstract
We study the phonon spectra of VI/III-V heterovalent superlattices (Si/GaAs, Si/AlAs, Ge/GaAs and Ge/AlAs) grown pseudomorphically on a (001)-oriented Ge or GaAs substrate by means of a planar force-constant model. Three possible interface configurations are considered, i.e. That the two interfaces in a period are composed of (i) two IV-III, (ii) two IV-V and (iii) IV-III and VI-V interfaces. It was found that confined modes could be well described by the bulk dispersions provided that the penetration parameter delta , which describes the penetration of a confined mode spreading into the second material, is properly chosen. In Ge/AlAs superlattices we find interface modes whose frequencies are slightly higher than that of the AlAs LO phonon at the Gamma point. Their vibrational amplitudes attenuate rapidly from the Ge-Al interface into the interior of Ge layers, but slowly into the interior of AlAs layers.
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