OPTICAL SPECTROSCOPY OF (001) GAAS AND ALAS UNDER MOLECULAR-BEAM EPITAXY GROWTH-CONDITIONS

Reflectance-difference (RD) studies were performed on variously reconstructed (001) GaAs and AlAs surfaces. The spectra of the (2 X 4) and (4 X 2) reconstructions on (001) GaAs show prominent features due to electronic transitions between lone-pair orbitals and dimer states, as previously identified by theoretical calculations. The spectra of the c(4 X 4) reconstructions on (001) GaAs and AlAs show similar features that we also interpret in terms of surface dimer excitations. These dimer features provide a capability of obtaining real-time, in situ information of dynamics on polar surfaces.