STUDIES OF THE PHONON-SPECTRA IN SI/GE SMALL-PERIOD SUPERLATTICES

The phonon spectra and phonon densities of states for Si/Ge small-period superlattices are calculated using the tetragonal supercell and the two-parameter Keating-type interaction in a three-dimensional formalism. We studied the Si10/Ge2 and Si9/Ge3 [001] superlattices, where the subscript indicates the number of atomic layers. The phonon spectra along the growth [001] direction agree with the previously calculated one-dimensional results. Phonons along the direction perpendicular to the growth direction are also studied. However, we focus on interface modes and Ge confined modes. The interface modes propagating in the (001) plane are nearly dispersionless, so the corresponding large density of states can be important for the electron-phonon interaction in modulation-doped superlattices. © 1990.