An investigation was made of the microscopic structure of (2 x 4) reconstructed (001) surfaces. Optical and electron spectroscopy of (001) surfaces which had been prepared under ultra-high vacuum was combined with first-principles calculations of energies. The symmetry, composition and surface optical anisotropy were characterized by means of low-energy electron diffraction, Auger electron spectroscopy photo-emission spectroscopy and reflectance anisotropy spectroscopy. It was found that the stable Ga-rich surface corresponded to a (2 x 4) reconstruction. No (4 x 2) reconstruction was observed; regardless of the preparation method. Depending upon the Ga coverage, 2 distinct lineshapes occurred in the reflection anisotropy spectra; thus indicating the existence of at least 2 different surface phases with (2 x 4) periodicity. This agreed with the total-energy calculations. Four (2 x 4) structural models could be stable; depending upon the chemical potentials of the surface constituents. All of the (4 x 2) structures which were considered were unstable. Mixed Ga-P dimers on top of the Ga-terminated substrate were suggested to be the ground-state geometry for the cation-rich phase of (001)-(2 x 4). The formation of P dimers at the surface was predicted for the more anion-rich phase.

(2 x 4) GaP(001) Surface - Atomic Structure and Optical Anisotropy A.M.Frisch, W.G.Schmidt, J.Bernholc, M.Pristovsek, N.Esser, W.Richter: Physical Review B, 1999, 60[4], 2488-94