REFLECTANCE ANISOTROPY SPECTROSCOPY OF ORDERED SB OVERLAYERS ON GAAS(110) AND INP(110)

The optical anisotropy of clean GaAs(110) and InP(110) cleaved surfaces, ordered Sb-p(1 X 1)-monolayers, and substrate-induced, ordered Sb multilayers was studied by means of reflectance anisotropy spectroscopy (RAS). The preparation was performed in UHV by deposition of 4-5 ML thick amorphous Sb films onto cleaved substrates and subsequent annealing steps which induce the ordering and, above 600 K, lead to the desorption of the Sb in excess of a single monolayer. In-situ Raman scattering experiments allow us to identify unambiguously the ordered multi- or monolayers by their different vibrational modes after each preparation step. RAS spectra of the clean surfaces show structures at the E1, E1 + DELTA1 and the E0', E2 gaps. The substrate-induced, ordered Sb multilayers exhibit a strong feature at 1.7 eV. The Sb monolayers reveal pronounced anisotropies around 2-2.7 eV, 3.0 and 4.3 eV. By comparison to the results of microscopic tight binding calculations the RAS signals around 2-2.7 eV can be attributed to transitions between mainly surface electronic states, whereas in the E1 and E0', E2 regions mainly surface perturbed bulk states contribute.