Interface reconstruction in GaAs/AlAs ultrathin superlattices grown on (311) and (001) surfaces

Phonon spectra of GaAs/AlAs superlattices (SLs) grown on (311)A, B and (001) surfaces were studied using Raman spectroscopy. The thickness of GaAs layers were varied from 1 to 10 monolayers (MLs); the thickness of AlAs barriers were 8 ML in the (311) direction. Different polarization geometries of Raman scattering were applied to study LO and TO modes. The splitting of TO(x) perpendicular to the facets on the (311)A surface) and TO(y) modes was observed for (311)A SLs. In the case of (311)B SLs no splitting was observed. The phonon anisotropy of (311)A SLs may be indirect evidence of anisotropic structure of quantum objects formed on the (311)A GaAs surface. In the Raman spectra of the SL containing GaAs submonolayers (SML) grown on a (2x4) reconstructed (100) surface, Raman peaks corresponding to additional lateral confinement of LO phonons were observed. The calculations of Raman spectra were carried out using the Born-von-Karman model (taking into account Coulomb interaction in the rigid-ion model) and the Wolkenstein bond polarizability model. According to the calculations, the interface structure strongly influences the Raman spectra of GaAs/AlAs heterostructures containing GaAs SML. (Author)