ELECTRONIC-PROPERTIES OF SB MONOLAYERS ON III-V(110) SURFACES DETERMINED BY RESONANCE RAMAN-SCATTERING

Resonance Raman scattering (RRS) experiments have been performed to explore the electronic states via the vibrational modes of highly ordered (1 x 1) monolayers of Sb on InP (110) and GaAs(I 10) prepared by thermal annealing. In accordance to the Cs symmetry of the two-atom unit cell of the monolayers three modes of A' and one of A'' symmetry are observed by Raman scattering. The scattering intensities show pronounced resonances which are related to electronic transitions between the two-dimensional electronic surface bands. The resonances are found to be characteristic for each vibrational mode. This can be understood in terms of different electronic bands being involved in the scattering process. For Sb on GaAs (110), the resonance of the A'' mode yields a maximum between 2.2 and 2.3 eV. On InP(110), resonances at 2.55 eV for the 1A', 2.3-2.6 eV for the 2A', 1.9 eV for the IA'' and greater-than-or-equal-to 3.0 eV for the 3A' modes occur. For both Sb on GaAs and InP the transition energies observed by RRS coincide with features reported by several other techniques. The resonance behavior of the ideal monolayers can be understood as a fingerprint of the joint density of states at the interface. In contrast, resonance Raman spectra taken after deposition of 1.5 ML Sb without annealing reveal a different resonance behavior. In this case, where the monolayer is not ideally ordered, the resonances are smeared out over an energy range between 2.3 and 2.7 eV revealing the influence of imperfections on the electronic band structure.