Oxidation of GaAs(110) with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">NO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>: Infrared spectroscopy

The oxidation of the GaAs(110) surface with ${\mathrm{NO}}_{2}$ has been studied by Fourier-transform infrared spectroscopy, molecular-beam techniques, and transport measurements. We find that ambient ${\mathrm{NO}}_{2}$ dissociatively adsorbs with an average low-coverage probability of 0.03 at room temperature and 0.14 at liquid-nitrogen temperature. In contrast, the molecular-sticking probability is greater than 0.5. We have identified the vibrational modes related to oxygen atoms, nitrogen atoms, NO, ${\mathrm{N}}_{2}$O, and dimerized ${\mathrm{NO}}_{2}$ adsorbed on the (110) surface. We find significantly different vibrational frequency distributions for oxygen atoms directly deposited on the surface compared to those derived from ${\mathrm{NO}}_{2}$ dissociative adsorption. Based on a variety of measurements we argue that ${\mathrm{NO}}_{2}$ dissociation requires steps or defects. Both vibrational spectra and transport properties indicate that a small fraction of the adsorbed oxygen atoms migrates into the bulk of the GaAs crystal, creating an electronic level in the band gap.

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