IN-SITU SPECTROSCOPIC ELLIPSOMETRY OF GAAS(001) SURFACE RECONSTRUCTIONS

GaAs(001) surface reconstructions prepared by molecular-beam epitaxy w ere studied in situ by spectroscopic ellipsometry (SE) and reflectance difference spectroscopy (or reflectance anisotropy spectroscopy) as a function of temperature. Simultaneous measurements of the dielectric function by SE and the reflectance difference Delta r/r allow us to id entify surface and bulk-related contributions to the optical anisotrop y Delta epsilon=epsilon(110)(-)-epsilon(110). For the (2x4), the c(4x4 ), and the (4x2) reconstructions we find resonances in Im(Delta epsilo n) at 2.9, 2.6, and 2.25 eV at T = 80 degrees C. Although the resonanc e at 2.9 eV coincides with the E(1) bulk transition and also shows the same temperature dependence, they can be distinguished, because the s urface contribution changes the sign when switching from the (2x4) to the c(4x4) reconstruction and the bulk contribution remains the same.