Abstract
Surface modification of InP by exposure to hydrogen polysulfide vapor at room temperature and by subsequent heating were studied by X-ray photoelectron spectroscopy (XPS). The XPS measured surface Fermi level ( E Fs ) position of polysulfide treated p-InP changed from 0.5 eV, relative to the valence band maximum (VBM), to 1.2 eV by heating the exposed surface at 300°C for a few minutes in vacuum. Further heating at 400°C for a few hours resulted in E Fs moving back to a position 0.5 eV above the VBM. Surface chemistry changes determined by XPS during this rather large movement of E Fs suggest a mechanism which involves the following three steps; (a) the exposure of InP to polysulfides reduces surface states in the bandgap; (b) heating of the exposed surface converts weakly adsorbed polysulfides to more strongly adsorbed species which contribute donor states near the conduction band minimum; (c) heating at 400°C slowly desorbs the surface donor species and gradually returns the E Fs of a p-substrate to its original 0.5 eV above the VBM.
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