Interpretation of reflectance anisotropy spectroscopy spectra of ZnSe(001) grown on GaAs(001) in terms of bulk, interface, and surface contributions

We combine reflectance anisotropy spectroscopy (RAS) with low energy electron diffraction, Auger electron spectroscopy, and soft x-ray photoemission spectra to analyze the surface optical anisotropy of ZnSe(OOl). Clean surfaces were prepared by thermal desorption of a protective Se cap from ZnSe layers of different thicknesses grown by molecular beam epitaxy on GaAs(001). Two surface reconstructions have been prepared by subsequent annealing, the Se-rich (2×1) reconstruction and the Zn-rich c(2×2) reconstruction. By modifying the surfaces either through submonolayer deposition of Sb or a short exposure to atmosphere it was possible to distinguish between surface and bulk/interface contributions to the optical anisotropy. Only on disordered, very Se-rich ZnSe(001) surfaces prepared at low annealing temperatures RAS features possibly related to electronic surface states are found. RAS spectra of the (2×1) and the c(2×2) surfaces are correlated with surface morphology and ordering rather than surface reconstruction and show features near the critical points of the bulk ZnSe band structure.