Long-wavelength nonpolar phonons in semiconductor heterostructures

Employing a phenomenological long-wavelength approach recently developed, both acoustic and optical phonons in nonpolar heterostructures are studied. Phonon modes in an arbitrary direction can be calculated without additional effort respect to high symmetry directions. A simple analytical expression for the dispersion relation in superlattices guides the physical discussion. We apply this to the calculation of phonon modes in unstrained short period isotopic Ge superlattices, in quantum wells and in strained short period Si/Ge superlattices. We find very good agreement with the results of other, more elaborated and costly calculations. Copyright Springer-Verlag Berlin/Heidelberg 2004