ADSORPTION OF CHLORINE ON GAAS(110) INVESTIGATED BY HIGH-RESOLUTION ELECTRON-ENERGY-LOSS SPECTROSCOPY

The adsorption of chlorine on cleaved GaAs(110) surfaces at room tempe rature was investigated by high-resolution electron energy-loss spectr oscopy (HREELS) and Auger electron spectroscopy (AES). Chlorine molecu les were released from an electrochemical Ag-AgCl-Pt cell. With AES, a dsorption of chlorine was observed to saturate at about 0.8 of a monol ayer. It is followed by an etching process which removes Ga atoms from the surface. After exposing the surfaces to Cl2, an adsorbate-induced energy-loss peak was found with HREELS which is identified as an adso rbate vibration. The width and the energetic position of this loss pea k vary as a function of chlorine coverage. Comparing this loss energy with vibrational energies of AsClBr2 and GaClBr2 molecules suggests to attribute the loss feature to Ga-Cl valence vibrations (430 cm-1, 53. 3 meV) for Cl coverages up to one monolayer and to As-Cl valence vibra tions (386 cm-1 47.9 meV) when etching occurs.