OPTICAL ANISOTROPY OF THE GAAS(001) SURFACE

The anisotropic optical response of (2 x 4) As-terminated and (4 x 2) Ga-terminated beta and beta 2 GaAs(001) surfaces is studied by using f irst-principles nonlocal pseudopotentials in a density-functional-theo ry framework within the local-density approximation. The calculated su rface dielectric function anisotropy agrees well with reflectance-diff erence spectroscopy experiments for the As-terminated beta 2 surface a nd for the Ga-terminated beta and beta 2 surfaces. Most of the calcula ted anisotropy comes from transitions involving only subsurface, bulkl ike electronic states that are perturbed by the surface; states confin ed at the surface, including those localized at the surface dimers, co ntribute little to the anisotropy.