Surface Structures of Clean and Sulfur-Treated GaP(111) A Studied Using AES, LEED, and STM

Surface structures of clean and sulfur-treated GaP(111) A have been studied by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). A GaP(111) A surface is reconstructed into a 2 X 2 structure by Ar ion sputtering and annealing at 450 degrees C. The 2 X 2 structure is for the first time imaged by STM. A surface structure model for the structure is discussed in terms of the cation-vacancy model. The sulfur-treated surface shows a 1 X 1 LEED pattern and the relative AES intensity of sulfur remains constant between 200-500 degrees C. The coverage of sulfur on the GaP(111) A surface is estimated to be about 0.82 monolayers. The sulfur is desorbed at about 550 degrees C where the LEED pattern was changed into a facet-like one. The different surface reconstructions (1 X 1-S and 2 X 2-S) on sulfur-treated III-V compound semiconductor (111) A surfaces are discussed in terms of the bond strength.