Understanding reflectance anisotropy: Surface-state signatures and bulk-related features in the optical spectrum of InP(001)(2X4)

A detailed analysis based on first-principles calculations with self-energy corrections is combined with photoemission spectroscopy to determine the o rigin of features observed in reflectance anisotropy spectroscopy (RAS) at semiconductor surfaces. Using the InP(001)(2x4) surface as a model case we obtain quantitative agreement between slab calculations and low-temperature RAS measurements. We find the contributions to the anisotropy signal relat ed either directly to surface states or to transitions between surface pert urbed bulk wave functions. Our results demonstrate the high sensitivity of RAS to the surface structure and chemistry and show that the absorption pro cesses causing the anisotropy signal take place in the uppermost few atomic layers of the substrate.