Origin of the optical anisotropy of GaAs (001)

We present a detailed experimental investigation of the room temperature op tical anisotropy of clean GaAs(001) surfaces, and of the change of this ani sotropy after exposure to oxygen. On the As-rich (2 x 4) surface, this anis otropy consists of two main signals, situated, respectively, near 3 and 4.5 eV. The results, together with the analysis of the anisotropy of Ga1-xAlxA s, lead us to the conclusion that the anisotropy near 3 eV originates mainl y from localized states related to surface dimers. However, the anisotropy near 4.5 eV is related to bulk-like optical transitions, since this anisotr opy is chemically insensitive, and since its spectral shape is similar to t hat of the bulk dielectric constant. (C) 1999 Elsevier Science B.V. All rig hts reserved.