Acoustic Phonons in a Si/Ge Supracrystal

The theoretical investigation of acoustic phonons in Si/Ge three-dimensional quantum dots superlattices (supracrystals) is presented. The acoustic phonon energy spectra are calculated in the framework of the face-centered cubic cell molecular-dynamic model. The dependencies of phonon density of states and phonon group velocity on the phonon energy are studied; the average phonon velocity is found to be close to zero in the wide range of phonon energies \(\hbar \omega > 10\) meV. The results allow us to predict the extremely low value of the lattice thermal conductivity in supracrystals and correspondingly high value of the thermoelectric figure of merit ZT.