Atomic Sites of S on (NH4)2Sx-Treated GaAs(100) Surface

Locations of S atoms on (NH4)2S x -treated GaAs(100) surfaces annealed at 200°C and 400°C have been studied on atomic scale by X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM) and medium-energy ion scattering (MEIS) using blocking. XPS spectra showed that the growth of native oxide layers on GaAs surfaces was suppressed after (NH4)2S x treatment and that most S atoms were bonded to only As or Ga atoms depending on the annealing temperature. STM observations revealed that S atoms on a GaAs(100) surface were reconstructed in a periodic structure of 1×1 in the case of annealing at 200°C, while 2×1 reconstruction was observed after annealing at 400°C. The distance between the S adsorbed layer and the uppermost layer of GaAs(100) could be estimated from the angle-resolved MEIS blocking spectra.