Phonons in semiconductor superlattices

Experimental results on phonons in semiconductor super-lattices are almost all from Raman scattering measurements. The superlattice system most studied is GaAs-Ga
1-x
Al
x
As, and in the best-understood geometry the phonons are longitudinal modes with wave vectors perpendicular to the (001) interface planes. A linear-chain model then gives a good understanding of the results, which show folding of the acoustic modes and confinement of the optic modes into "phonon quantum wells." Modes propagating obliquely to the interfaces are either slab modes or interface modes. They have been less studied but can be explained using the dielectric model. A more thorough model is needed that takes into account both the coulomb interaction and the effects of the short-range interactions (spatial dispersion). Some results obtained on other semiconductor superlattices will also be discussed.