Fluorine adsorption on GaAs(110) surfaces and the onset of etching after XeF2 exposures

The interaction of XeF2 molecules with GaAs(110) surfaces was investigated with high-resolution electron energy-loss (HREELS) and Auger electron spectroscopy (AES) in the exposure range between 1 and 1000 langmuir (L). The AES results show that up to XeF2 doses of approximately 100 L, fluorine atoms are mainly chemisorbed on GaAs(110) surfaces. After XeF2 exposures above 100 L, etching of the GaAs(110) surface occurs by removing arsenic atoms. Adsorbed xenon atoms were never detected. In the chemisorption range an energy-loss structure which is attributed to AsF valence vibrations is observed in the HREEL spectra. The excitation energy of the AsF vibration shifts from 670 cm−1 (84 meV) at very low fluorine coverages to 720 cm−1 (90 meV) at 0.3 monolayers. This finding may be explained by a mutual electrostatic interaction between AsF surface dipoles and their images. From that and by use of dielectric theory an effective dynamic charge of the vibrating AsF surface molecules is estimated. In the etching regime this AsF loss structure disappears and a broad feature at about 575 cm−1 (71.3 meV) is observed which may be due to vibrations of GaFx groups.