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

The optical anisotropy of clean GaAs(110) and InP(110) cleaved surface s, ordered Sb-p(1 X 1)-monolayers, and substrate-induced, ordered Sb m ultilayers was studied by means of reflectance anisotropy spectroscopy (RAS). The preparation was performed in UHV by deposition of 4-5 ML t hick amorphous Sb films onto cleaved substrates and subsequent anneali ng steps which induce the ordering and, above 600 K, lead to the desor ption of the Sb in excess of a single monolayer. In-situ Raman scatter ing experiments allow us to identify unambiguously the ordered multi- or monolayers by their different vibrational modes after each preparat ion step. RAS spectra of the clean surfaces show structures at the E1, E1 + DELTA1 and the E0', E2 gaps. The substrate-induced, ordered Sb m ultilayers exhibit a strong feature at 1.7 eV. The Sb monolayers revea l pronounced anisotropies around 2-2.7 eV, 3.0 and 4.3 eV. By comparis on to the results of microscopic tight binding calculations the RAS si gnals around 2-2.7 eV can be attributed to transitions between mainly surface electronic states, whereas in the E1 and E0', E2 regions mainl y surface perturbed bulk states contribute.