Micro-Raman scattering study of InGaAs/(AlAs)/AlAsSb quantum wells grown by molecular beam epitaxy

Raman spectra of In0.80Ga0.20As/(AlAs)/AlAs056Sb0.44 quantum wells (QWs) grown on (0 0 1)-InP substrates by molecular beam epitaxy were measured in backscattering along Z||[001] and x||[110] directions, i.e. from (0 0 1) grown and (1 1 0) cleaved surfaces, with microprobes. Confined longitudinal-optic (LO) and transverse-optic (TO) phonons with wave vector q either parallel or normal to the Z axis were studied in all the independent scattering geometries. The Raman scattering spectra from (0 0 1) surfaces show two-mode behavior in the InGaAs band, while single mode behavior is confirmed in the AlAsSb band, consistent with the previous results. The GaAs-like LO- phonon peak splits into two peaks that can be attributed to the confined GaAs-like LO-phonon mode and the intermediate frequency plasmon-LO-phonon coupled mode. A drastic change in the Raman spectra is observed when the transferred momentum is changed from the Z-axis to x-axis. The Raman spectra in the x(Zy)x¯ geometry are dominated by TO-confined phonons, whereas LO-confined phonons are dominated in the x(ZZ)x¯ geometry, consistent with the selection rules, although in other configurations no signals are observed inconsistent with the selection rules.