Optical anisotropy of (001)-GaAs surface quantum wells

Abstract

We report a reflectance difference spectroscopy (RDS) study of the optical anisotropy of GaAs:(001) surface quantum wells consisting of a thin GaAs layer (3--30 nm thick) embedded between an arsenic reconstructed surface and an AlAs barrier. The RDS spectra display anisotropic contributions from the free surface and from the GaAs/AlAs interface. By comparing RDS spectra for the $c(4\ifmmode\times\else\texttimes\fi{}4)$ and $(2\ifmmode\times\else\texttimes\fi{}4)$ surface reconstructions, we separate these two contributions, and demonstrate that the anisotropy around the ${E}_{1}$ and ${E}_{1}+{\ensuremath{\Delta}}_{1}$ transitions comprises a component originating from modifications of bulk states near the surface. The latter is attributed to anisotropic strains induced by the surface reconstruction. The experimental data are well described by a model for the RDS response of the multilayer structures, which also takes into account the blue energy shifts and the changes in oscillator strength of the ${E}_{1}$ and ${E}_{1}+{\ensuremath{\Delta}}_{1}$ transitions induced by quantum-well confinement.