Raman scattering was used to study optical phonons in a Si12Ge4 strained‐layer superlattice on c‐Si(001) that was subjected to hydrostatic pressure at room temperature. The change of phonon frequency with pressure, dω/dP, for the principal quasi‐confined LO mode in the Ge layers, is found to be significantly smaller than that for bulk crystalline Ge. This difference is shown to be due to the tuning of biaxial strain in the Ge layers and the pressure response of the confined mode as hydrostatic pressure is varied. Both strain and confinement make comparable contributions to dω/dP for the Ge layers in the superlattice examined here.

http://www.columbia.edu/~iph1/Download/Sui-SiGeSL-HighP-1991-ApplPhysLett_58_2351.pdf

Raman analysis of Si/Ge strained-layer superlattices under hydrostatic pressure

Revue de la theorie des phonons optiques dans les super-reseaux (SL) dans le cadre des approches macroscopiques. On demontre que les modes des phonons optiques de SL peuvent etre obtenus comme des solutions propres d'un probleme aux valeurs propres enonce. Ce dernier comprend l'equation de Born-Huang pour le champ de deplacement relatif, generalisee par l'inclusion des forces mecaniques a longue distance, l'equation de Bloch, et la condition d'hermiticite. Cette derniere conduit a la quantification des nombres d'onde des phonons confines. Les solutions propres peuvent etre classees suivant leurs origines (volume, interface...) et les vortexes. Consideration de l'interaction des phonons avec les electrons. Cette theorie macroscopique donne la dispersion des vecteurs d'onde des modes des phonons. Consideration de la diffusion Raman et de la diffusion des porteurs libres

Optical Phonons in Superlattices

Chapter 5 - Optical Properties

Raman spectra from Si/Ge superlattices with disordered interface layers

The simple example of phonons in a linear chain of atoms with substitutional disorder is reconsidered in order to determine the rearrangements of acoustic and localized mode branches with increasing concentration of light impurities. The coherent-potential approximation cannot be applies successfully to this problem. A new expression for the self-energy of phonons is derived, which is exact in the limits of c to 0 and c to 1, c being the impurity concentration, and which gives reliable results for intermediate c.

Phonons in mixed crystals

Le formalisme utilise permet de calculer la fonction de Green dans la representation mixte pour un superreseau ayant un general de monocouches. Les couches desordonnees sont decrites dans l'approximation du potentiel coherent. Deux sortes d'arrangement sont etudies. Les resultats montrent la sensibilite du spectre de phonons vis-a-vis de la coherence a longue distance de la composition chimique des superreseaux et de la perfection de leur preparation

J. Maek

Papers

Influence of alloy disorder on the vibrational properties of Si/Ge superlattices.