A REFLECTANCE ANISOTROPY SPECTROSCOPY STUDY OF MOLECULAR SULFUR ADSORPTION ON THE GAAS(100) SURFACE

The interaction of molecular sulfur with the GaAs(100) surface has been investigated by reflectance anisotropy spectroscopy (RAS). The use of arsenic-capped GaAs(100) surfaces provided a means to study the interaction of sulfur with both the arsenic-rich (2X4) and gallium-rich (4X1) surface reconstructions. A sulfur flux was generated in ultra-high-vacuum (UHV) by the thermal decomposition of silver sulfide. The room-temperature deposition of a 1-2 monolayer saturation coverage of sulfur on both arsenic- and gallium-rich surfaces produces a (1X1) low-energy electron-diffraction pattern. This surface displays a strongly anisotropic optical response with RAS spectra which contain two clear features at 3.5 and 5.2 eV. These features become more pronounced as the sulfur-covered surface is annealed up to 500 degrees C where the surface displays a (2X1) reconstruction. The origin of these spectral features is believed to be due to optical transitions related to the sulfur dimers which are formed on this surface. The extent of the reduction in surface band bending induced by the sulfur coverage can be monitored by measuring the magnitude of the linear electro-optic feature which appears prominently in the RAS spectra of high-doped GaAs samples. (C) 1995 American Institute of Physics.