PHONONS IN VI III-V HETEROVALENT SUPERLATTICES/

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 mo del. Three possible interface configurations am considered, i.e. that the two interfaces in a period are composed of (i) two IV-III, (ii) tw o IV-V and (iii) IV-II and VI-V interfaces. It was found that confined modes could be well described by the bulk dispersions provided that t he penetration parameter delta, which describes the penetration of a c onfined mode spreading into the second material, is properly chosen. I n Ge/AlAs superlattices we find interface modes whose frequencies are slightly higher than that of the AlAs LO phonon at the GAMMA point. Th eir vibrational amplitudes attenuate rapidly from the Ge-Al interface into the interior of Ge layers, but slowly into the interior of AlAs l ayers.