Raman and photoluminescence studies of the interface reconstructions in GaAs/AlAs superlattices grown on (311) and (001) surfaces

The GaAs/AlAs superlattices (SLs) grown on facet surfaces (311)A,B and (100) surface were studied using Raman and photoluminescence (PL) spectroscopy. Sharp differences in Raman and PL spectra of the ultrathin SLs grown on (311)A and (311)B surfaces were observed, These effects probably are result of differences in interface reconstructions, The observed phonon anisotropy of (311)A SLs can be indirect evidence of anisotropic structure of surface quantum objects formed on (311)A Ga-As. The PL peaks of (311)A and (311)B SLs differ both the intensities and the positions. In the Raman spectra of the SL containing GaAs submonolayers grown on (2x4) reconstructed (100) surface, the triplet Raman peak, corresponding to scattering on GaAs-like confined LO phonons was observed, The triplet structure appears due to additional lateral confinement of LO phonons in GaAs quantum islands. Calculations of Raman spectra were carried out using the models of rigid ions, bond charge and Wolkenstain bond polarisability. The theoretical Raman spectra of the islands grown (in the context of a known model) on the (001)-(2x4) reconstructed surface are in surprisingly good agreement with the experimental ones, The calculations show that 70 % of the islands contains less than 18 Ga atoms, what is in very good agreement with the known STM data.