GaP(001) and InP(001): Reflectance anisotropy and surface geometry

We have investigated the optical anisotropy of GaP(001) and InP(001) surfac es. The samples were prepared by homoepitaxial metalorganic vapor phase epi taxy growth and either directly transferred into ultrahigh vacuum (UHV) or in situ capped and, after transfer, decapped in UHV by thermal desorption o f a P/As capping layer. Symmetry, composition, and surface optical anisotro py were characterized by low-energy electron diffraction, Auger electron sp ectroscopy, and reflectance anisotropy spectroscopy. We observe (2 X 1)/(2 X 2)-like reconstructions for the very P-rich and (2 X 4) reconstructions f or the more cation-rich surfaces. No (4 X 2) reconstruction could be prepar ed, independent of the preparation method. A comparison of the reflectance anisotropy between GaP(001) and InP(001) surfaces shows similar line shapes for the very cation-rich (2 X 4) surfaces. For less cation-rich surfaces, however, we observe distinct differences between the spectra of the two sys tems. In both cases, different line shapes in the reflection anisotropy spe ctra occur for the (2 X 4) periodicity, suggesting the existence of differe nt (2 X 4) geometries. The experimental results are discussed on the backgr ound of atomic structures, total energies and reflectance anisotropy spectr a obtained ab initio from density-functional theory local-density approxima tion calculations. (C) 1999 American Vacuum Society. [S0734-211X(99)03504-0 ].