BONDING STATES OF CHEMISORBED SULFUR-ATOMS ON GAAS

The chemistry of the S/GaAs system is studied using synchrotron radiation photoemission spectroscopy. Monolayer-order sulfur atoms are successfully chemisorbed on clean n-GaAs (001) surfaces at room temperature by using an Ag/AgI/Ag2S/Pt electrochemical cell, which generates an atomic sulfur flux. Photoemission spectra of core levels are measured with a photon energy of about 210 eV before and after annealing at 360-degrees-C for 10 min in vacuum. Ga 3d, As 3d, and S 2p spectra indicate that Ga-S and As-S bonds are formed on the as-chemisorbed GaAs surfaces at room temperature, and that Ga-S bonds become dominant after annealing at 360-degrees-C. These results are the same as for the (NH4)2S(x)-treated n-GaAs surfaces. It is found that the Ga-S bonding formation is the key for passivating GaAs surfaces for both sulfur-chemisorbed and (NH4)2S(x)-treated GaAs.