A microscopic calculation of the surface optical properties of Si(111) and Si(110) within the randomphase approximation is presented. Surface effects on optical matrix elements are found important in order to explain the anisotropic reflectance observed at surfaces of cubic semiconductors. At frequencies above the bulk indirect gap, a large contribution to differential reflectivity turns out to be related to the structural changes occurring upon oxidation.

• Received 2 January 1986

DOI:https://doi.org/10.1103/PhysRevB.33.8885