Atomic structure and electronic properties of HCl-isopropanol treated and vacuum annealed GaAs(100) surface

The HCl-isopropanol treated and vacuum annealed GaAs(100) surface was studi ed by means of AES, XPS, HREELS and LEED. The chemical treatment and sample transfer into UHV were performed under N-2 atmosphere. The HCl-isopropanol treatment removes gallium and arsenic oxides from the surface leaving behi nd about two monolayers of excess arsenic. The residual carbon contaminatio n was around 0.2-0.4 ML. Bending and stretching C-H modes were observed in HREELS spectra and attributed to the CH2 and CH3 radicals. This hydrocarbon contaminations were removed from the surface together with the excess arse nic by vacuum annealing at 300-420 degrees C. LEED measurements of the chem ically treated surface showed spotty (1 X 1) patterns even before annealing . These patterns became sharper after annealing in the temperature range 25 0-400 degrees C. At higher temperatures LEED patterns changed to (2 X 4)/c( 2 X 8), (2 X 6), (3 X 1)/(3 X 6), (4 X 1) and (4 X 2)/c(8 X 2) reconstructi ons. The XPS results indicated weak regular movement of the Fermi-level wit hin about 150 meV in the 250-600 degrees C annealing temperature range. We observed systematic variations of work function and electron affinity up to 550 meV with the maximum and minimum for the (2 X 4)/c(2 X 8) and (4 X 1)/ c(8 X 2) structures, respectively. These variations are due to a charge tra nsfer between the top two surface layers (Ga and As) of the crystal. (C) 19 99 Elsevier Science B.V. All rights reserved.