RAMAN-SCATTERING FROM PERIODIC AND NONPERIODIC GASB/ALSB STRAINED-LAYER LATTICES

Raman scattering measurements have been performed on a series of periodic and nonperiodic strained-layer GaSb/AlSb lattices. In the optical frequency region quantum confined longitudinal optic phonons are observed in GaSb layers when the layer width is less than 25 Angstrom. Spatially extended interface modes lying within the LO-TO regions for both GaSb and AlSb are also seen. The interface mode frequencies are not well fit by current macroscopic theories. The confinement-induced GAMMA -to -L crossover in GaSb manifests itself via the observation of a scattering structure which resembles the optical phonon density of states. In structures grown with supercell or nonperiodic symmetry, the acoustic spectra display zone folding as well as nominally forbidden modes whose frequencies lie close to but are not exactly coincident with zone boundary phonons. Acoustic phonons in a quasiperiodic Fibonacci lattice have been measured and compared to periodic rational approximant lattices with (ABAAB) or (ABAABAAB) repeat units.