Atomic structure of GaP (110) and (111) faces

Abstract

Low energy electron diffraction (LEED) intensities have been measured for the (110) and (111) faces of GaP. The LEED intensities of the (110) face have been analyzed using a dynamical multiple-scattering model of the diffraction process. The intralayer multiple scattering is treated exactly, while for the interlayer multiple scattering, the renormalized-forward-scattering method is used. Comparison of the calculated and observed LEED intensities suggests that both the Ga and the P atoms on the (110) face may exhibit a contracted outermost layer spacing with a rippled geometry. The surface layer is compressed by about 5% such that the top layer spacing is reduced by 0.1 Å. The P atoms protrude from the surface, whereas the Ga atoms are displaced inward such that no nearest-neighbor bond lengths are altered. LEED intensity analysis of the first order beams indicates that the bond-rotational angle ω is approxiimately 27 °. The quality and stability of the LEED patterns of the Gap (110) and (111) faces have been compared with the LEED patterns of the GaAs (110) and (111) faces. It is concluded that the Gap (110) face is less stable than the GaAs (110) face, but the Gap (111) face is far more stable than the GaAs (111) face. Phosphorus atoms start vaporizing from the GaP (111) face at an annealing temperature of 650 °C. Continued heating at 650 °C for 10 min resulted in a complete vaporization of phosphorus atoms and left a pure gallium surface layer on the GaP (111) face. A clear 1×1 threefold symmetry LEED pattern was observed on this Ga and Gap (111) surface. This indicates that the gallium atoms crystallize on the Gap (111) face and it appears reasonable to conclude that a good Schottky contact would be relatively easy to obtain on the GaP (111) face.