Recently, sulfur treatments have been reported which passivate the InP and GaAs surfaces. From the variety of experiments reported on sulfurized surfaces, it is clear that the treatments can improve the electronic properties, however, the chemistry of the surface after the treatments has not been fully explained. We have applied X-ray photoelectron spectroscopy to determine the bonding of the InP and GaAs surfaces after a variety of sulfur treatments. Based on these data and that reported in the literature, we propose a model in which the sulfur at low temperature only chemisorbs on the surface and does not break back-bonds or intermix with the substrate. We postulate that thermodynamics does not determine the low temperature surface chemistry. Instead, the wet chemistry processing plays the major role since it determines which species of the substrate atoms will terminate the surface. The GaAs appears to be As terminated and hence As-S chemisorption bonds primarily occur. On InP the S bonds to the surface In atoms.
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