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The chemisorption and the reaction of chlorine and hydrogen chloride on the GaAs(100)-4 × 6 surface at 110 K are investigated using soft X-ray photoelectron spectroscopy which employs synchrotron radiation. At low exposures, Cl 2 and HCl dissociate and preferentially adsorb on the As atom, which causes As-Ga bond breakage to initiate chlorination of the Ga atom. As x Cl is proposed to form at initial chlorination, in which the Cl atom is bonded to a high coordination site. Subsequently, various AsCl x and GaCl x (x ) 1, 2, and 3) species are formed on the GaAs surface, and their corresponding chemical shifts are assigned. At high exposures, chlorination of the GaAs surface is saturated, and the surface is mainly covered with physisorbed Cl 2 and HCl molecules. Synchrotron radiation on the chlorinated GaAs surface stimulates both the photodesorption of Ga and As chlorides and the photodissociation of physisorbed Cl 2 molecules. A potential route for anisotropic cryogenic etching of the GaAs surface by the chlorine-containing compound under photon irradiation is discussed.

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The adsorption and thermal reaction of H 2 S on the InP(100) surface is studied by synchrotron radiation (SR) soft X-ray photoelectron spectroscopy. In addition to molecular adsorption, H 2 S decomposes to form the dissociative species of S, HS, and H on the surface at 100 K. The S atom of the sulfide species preferentially bonds to the In atom, and the H atom generated by the H 2 S dissociation bonds to the P atom. H 2 S molecules may physisorb on the surface in the form of an icelike multilayer/cluster at low temperatures, even at low coverages. The irradiation of SR white light can induce an alternative reaction of H 2 S with the InP surface to form a thicker sulfur layer than that obtained by thermal deposition. The resulting sulfur layer may provide chemical protection for the InP substrate from further reaction.

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