Effect of adlayer dimer orientation on the optical anisotropy of single domain Si(001)

The effect of adlayer dimer formation on the optical anisotropy of single domain Si(001) is reported. Reflection anisotropy spectroscopy (RAS) from Ga and Sb adsorbed on the Si(001) surface reveals complex behavior which depends strongly on the atomic species and the RAS signal cannot be simply related to dimer orientation. Dimer formation in the same direction on the surface by Si and Ga is shown to produce RAS signals, below the direct optical gap of Si, of the opposite sign. This contrasts with the simpler behavior observed for Ga and As adsorption on GaAs(001) surfaces.