CONTROLLING SURFACE BAND-BENDING OF INP WITH POLYSULFIDE TREATMENTS

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 beating the exposed surface at 300-degrees-C for a few minutes in vacuum. Further beating at 400-degrees-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-degrees-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.