TOPOGRAPHIC AND CRYSTALLOGRAPHIC CHARACTERIZATION OF A GRAZING-ION-BOMBARDED GAAS(110) SURFACE BY TIME-OF-FLIGHT ION-SCATTERING SPECTROMETRY

We studied the topography and the atomic structure of a clean GaAs(110 ) surface by time-of-flight ion-scattering spectrometry (TOF-ISS). In a first series of measurements the surface was cleaned by standard cyc les of ion bombardment and annealing (500 eV Ar+, 500 degrees C). This method was very efficient to remove surface contaminants but not to s mooth out the damage produced in TOF-ISS experiments. A cleaning metho d consisting of grazing bombardment with 20 keV Ar+ combined with anne aling at 500 degrees C resulted in a clear improvement of the surface flatness. This was confirmed by measurements of electron energy distri butions recorded under grazing proton bombardment and by a topographic al analysis with an atomic force microscope. The crystallographic stru cture of the grazing ion bombarded surface was then studied by TOF-ISS . The quasisingle backscattered intensity measured for 5 keV Ne+ prese nted strong variations with the incident and azimuthal angles which ar e consistent with the generally accepted relaxed GaAs(110) surface. Fr om the comparison of critical angles measured and focusing regions cal culated with a code recently developed we have obtained an As-Ga first interlayer spacing Delta Z = (0.66 +/- 0.08) Angstrom, and the spacin gs between the first and second As layers Delta Z(1,2)(As) = (2.25 +/- 0.08) Angstrom and between the first and second Ga layers Delta Z(1,2 )(Ga) = (1.57 +/- 0.1) Angstrom.