SULFUR BONDING TO GAAS

This paper presents experimental results on sulfur bonding to etched GaAs surfaces which have an As/Ga ratio ranging from 0.6 to 6.0. The source of the sulfur was either a liquid solution of Na2S or (NH4)2S, or gaseous H2S applied in a N2 purged glove box. Angle resolved x-ray photoelectron spectroscopy (XPS) spectra was obtained from approximately 40 different samples in order to determine the concentration of the various surface chemical species and their bonding state. Most of the experiments were conducted with H2S exposed samples at substrate temperatures from 30 to 350-degrees-C. Sulfur is shown to bond to both Ga and As. The amount of bonding to each depends on the As/Ga ratio. This is true for both H2S and the liquid S solutions. Only one S-As bonding state was observed, independent of the S treatment process. S was observed to bond to elemental As and substrate As with the same binding energy and concentration. H2S exposed surfaces had a higher concentration of S than did those that were treated with Na2S or the (NH4)2S.