Terrace and step contributions to the optical anisotropy of Si(001) surfaces - art. no. 045322

The contributions of atomically flat terraces as well as of S-A, S-B, and D -B steps to the optical anisotropy of Si(001) surfaces have been calculated using a real-space multigrid method together with db initio pseudopotentia ls. Our results for ideal (1x2), p(2x2), and c(2x4) reconstructed surfaces show a distinct influence of the dimer arrangement on the optical spectra. The calculated spectrum for the Si(001)c(2x4) surface agrees best with the signal measured for atomically smooth terraces. The significant optical ani sotropy around 3 eV observed for vicinal surfaces, however, is induced by s urface steps. Both electronic transitions directly at the surface as well a s in deeper layers contribute to the optical anisotropy. We identify two me chanisms causing anisotropy signals from layers beneath the surface: the in fluence of the anisotropic surface potential on the bulk wave functions as well as minor contributions from atomic relaxations caused by surface-induc ed stress.