ISSN - 01694332, Applied Surface Science, 1999, vol. 142, p. 75-80
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 studied by means of AES, XPS, HREELS and LEED. The chemical treatment and sample transfer into UHV were performed under N2 atmosphere. The HCl-isopropanol treatment removes gallium and arsenic oxides from the surface leaving behind about two monolayers of excess arsenic. The residual carbon contamination 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 arsenic by vacuum annealing at 300-420°C. LEED measurements of the chemically treated surface showed spotty (1 × 1) patterns even before annealing. These patterns became sharper after annealing in the temperature range 250-400°C. At higher temperatures LEED patterns changed to (2 × 4)/c(2 × 8), (2 × 6), (3 × 1)/(3 × 6), (4 × 1) and (4 × 2)/c(8 × 2) reconstructions. The XPS results indicated weak regular movement of the Fermi-level within about 150 meV in the 250-600°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 × 4)/c(2 × 8) and (4 × 1)/c(8 × 2) structures, respectively. These variations are due to a charge transfer between the top two surface layers (Ga and As) of the crystal.