Chemical passivation of InSb (100) substrates in aqueous solutions of sodium sulfide

The elemental composition and electronic structure of both native-oxide-covered InSb (100) substrates and substrates treated in aqueous solutions of sodium sulfide are analyzed by X-ray photoelectron spectroscopy. It is found that, as a result of treatment in a 1 M aqueous solution of Na$_2$S and subsequent annealing in vacuum at 150$^\circ$C, the surface layer consisting of complex antimony and indium oxides of nonstoichiometric composition is removed completely with the formation of a continuous layer of chemisorbed sulfur atoms coherently bound to indium atoms. According to atomic-force microscopy data, no etching of the host substrate material occurs during sulfide passivation. A shift (by 0.37 eV) of the In–Sb bulk photoemission towards higher binding energies is found, which indicates that the surface Fermi level shifts deeper into the conduction band.