SELENIUM-TERMINATED AND TELLURIUM-TERMINATED GAAS(100) SURFACES OBSERVED BY SCANNING-TUNNELING-MICROSCOPY

GaAs(100) surfaces with adsorbed Se or Te have been studied using scan ning tunneling microscopy (STM), x-rav-photoemission spectroscopy (XPS ), and electron diffraction, STM reveals uniform dimerization which is consistent with the 2 X 1 symmetry of the electron diffraction. XPS s hows an initial single-monolayer coverage of Se followed by a slow Se uptake which predominantly replaces As. Narrow single- and double-bila yer high islands, which are long in the [011] direction of dimer rows, are generally observed as well as terrace edges which show related ki nk anisotropy. Possible surface structures are discussed.