The properties of (NH4)2Sx-treated (001) surfaces were studied by using X-ray photo-electron spectroscopy, X-ray photo-electron diffraction, and reflection high-energy electron diffraction techniques. A (2 x 1) surface reconstruction was observed, on substrates which had been heated in vacuum, at a transition temperature of about 200 to 350C. The S atoms were bonded only to In atoms, and exchanges between P and S occurred in the first 5 atomic planes, leading to the formation of an InP1-xSx pseudomorphic overlayer. The S surface concentration ranged from about 0.85 of a monolayer, after annealing at 350C, to 0.5 of a monolayer at 550C. The sulfidation treatment produced (2 x 1) reconstructed surfaces which were highly stable at temperatures of up to 560C. Unpinned ultra-clean surfaces, free of C and O, were obtained by vacuum annealing at 550C.

D.Gallet, G.Hollinger: Applied Physics Letters, 1993, 62[9], 982-4