Raman Scattering in GaSb/AlSb Strained-Layer Lattices.

Raman scattering has been used to study the folded acoustic mode structure associated with GaSb/AlSb strained-layer lattices which exhibit periodic, quasiperiodic, or random sequencing of the individual layers. In periodic superlattices grown on (001) and ([EQ]111 bar[EN])-oriented substrates, the dominant modes consist of the respective symmetry allowed folded transverse and/or longitudinal acoustic phonons. On (001) substrates, symmetry forbidden transverse acoustic mode scattering peaks are sometimes observed. Their presence does not correlate directly with either macroscopic roughness or the strain present due to the lattice mismatch. Additional peaks have also been observed for which we cannot presently suggest an assignment. The reduced Raman spectrum of a quasiperiodic lattice with Fibonacci layer sequencing was found to exhibit no fewer than nine dips. The latter can be indexed accurately using an expression derived by Merlin and coworkers. The finite length scale associated with Raman scattering in a highly absorbing medium was found to manifest itself in the detection of residual structure representing remnant quasiperiodicity in a lattice with random ordering of the respective layers.