Effect of low-intensity laser radiation during oxidation of the GaAs(110) surface

Abstract

Considerable interest in the use of laser irradiation as a means of processing (annealing, cleaning, alloying, etc.) semiconductor materials, as well as the importance of the oxygen surface chemistry on III-V semiconductors, has led us to study the effect of low-intensity (?3 W/cm2) laser radiation on the oxidation behavior of (110) surfaces of GaAs cleaved in UHV (<10−10 Torr). The oxygen sticking probability in the submonolayer coverage range has been increased by a factor of 103 (from a probability of ∠10−9 to ∠10−6) by uniform irradiation of the GaAs surface with a continuous wave Ar+ laser (λ = 5145 Å) during the oxygen exposure. We find the data cannot be explained in terms of either heating of the surface or excitation of the oxygen by the laser radiation; it appears that the most likely explanation of the phenomena is an increase in the density of electrons and/or holes at the surface. A limiting step in the oxygen uptake process is the breakup of the oxygen molecule; this dissociation would be increased by increasing the number of electrons at or near the surface. In chemical terms, the reconstructed GaAs surface has no orbitals suitable for binding oxygen—such orbitals can be provided by changing the charge state of a surface atom via optical excitation.