We report the first systematic study of above—band-gap optical anisotropies in cubic semiconductors. The anisotropies are large, of the order of 1%. The dominant intrinsic contributions for (110) Si and Ge are due to surface many-body screening and bulk spatial dispersion. Extrinsic contributions from chemisorbed and physisorbed species also play important roles.

• Received 24 August 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.1956