CHEMICAL, STRUCTURAL, AND ELECTRONIC-PROPERTIES OF SULFUR-PASSIVATED INP(001) (2X1) SURFACES TREATED WITH (NH4)2SX

Some chemical, structural, and electronic properties of (NH4)2Sx-treated InP(001) surfaces have been studied using x-ray photelectron spectroscopy, x-ray photoelectron diffraction and reflection high-energy electron diffraction. A (2X1) surface reconstruction is observed for substrates heated in vacuum at a transition temperature of about 200-350-degrees-C. Sulfur atoms are only bonded to indium atoms and the exchange between phosphorus and sulfur occurs in the first five atomic planes leading to the formation of an InP1-xSx pseudomorphic overlayer. The sulfur surface concentration varies from about 0.85 +/- 0.15 after annealing at 350-degrees-C to 0.5 +/- 0.15 monolayer at 550-degrees-C. The sulfidation treatment results in (2 X 1) reconstructed surfaces of high thermal stability up to 560-degrees-C and of high chemical stability. Unpinned ultraclean surfaces, free of carbon and oxygen, are obtained after vacuum annealing at 550-degrees-C.