Surface structure of phosphorus-terminatedGaP(001)−(2×1)

Abstract

The surface structure of phosphorus-terminated $\mathrm{Ga}\mathrm{P}(001)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ has been studied by low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and synchrotron radiation photoemission spectroscopy. HREELS spectra indicate that hydrogen is adsorbed on the surface, leading to formation of a $\mathrm{P}\mathrm{H}$ bond. The intensity of the stretching vibration of the $\mathrm{P}\mathrm{H}$ remains constant for the $(2\ifmmode\times\else\texttimes\fi{}1)$ surface annealed at $300--600\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, where $(2\ifmmode\times\else\texttimes\fi{}1)$ LEED patterns also remain. The vibration mode and patterns disappeared simultaneously upon annealing at $700\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. STM filled state images show zigzag chain structures. On the other hand, straight rows along the [110] direction are seen in the empty state images. Surface core-level shifts are found: $+0.60\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for $\mathrm{Ga}\phantom{\rule{0.2em}{0ex}}3d$ and $\ensuremath{-}0.69$ and $+0.39\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for $\mathrm{P}\phantom{\rule{0.2em}{0ex}}2p$. These results can well explain a theoretical model of buckled P-dimers with hydrogen adsorbed in an alternating sequence.