X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY ON INP TREATED BY SULFUR-CONTAINING-COMPOUNDS

Surface chemistry, and surface Fermi level (E(Fs)) changes on InP, as a result of exposure to several sulfur compounds, and of subsequent heating were studied by x-ray photoelectron spectroscopy. It was found that after p-InP samples were exposed to a mixture of hydrogen sulfide - and polysulfide, heating at 200-300-degrees-C induced a strong type-inversion of the semiconductor surface. However, subsequent heating at 400-degrees-C returned E(Fs), towards the valence band maximum (VBM). From many repeated experiments, E(Fs), was found to be changed in the range of 0.5-1.2 eV (referenced to VBM). Further studies on exposure to other sulfur compounds including hydrogen sulfide, sulfur, and sulfur dioxide showed that the large range of E(Fs) movement correlated only with polysulfide. The overall spectral results suggest that adsorption of hydrogen polysulfide reduced surface states in the band gap of InP and led to the formation of donor states near the conduction band minimum of InP upon heating at 200-300-degrees-C. Further heating at 400-degrees-C desorbed the donor species and returned E(Fs) towards the VBM.