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Comparison of Low Intensity Laser Enhancement of Oxygen Chemisorption on GaAs Using O2 and N2O

Published online by Cambridge University Press:  28 February 2011

K. A. Bertness ,
C. E. McCants ,
T. T. Chiang ,
P. H. Mahowald ,
A. K. Wahi ,
T. Kendelewicz ,
I. Lindau  and
W. E. Spicer
K. A. Bertness
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
C. E. McCants
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
T. T. Chiang
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
P. H. Mahowald
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
A. K. Wahi
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
T. Kendelewicz
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
I. Lindau
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
W. E. Spicer
Affiliation:
Stanford Electronics Laboratories, Stanford University, Stanford, CA 94305
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Abstract

The sticking coefficient for molecular oxygen on GaAs(110) up to about one-halft monolayer coverage can be enhanced by two or three orders of magnitude when the semiconductor surface is illuminated by an argon ion laser with intensities of 5 W/cm2 or less. Previous work has shown that this effect is nonthermal and roughly independent of wavelength for above-bandgap radiation, implying that photogenerated electrons and/or holes are responsible in some way. In this paper we present recent work which shows that transfer of energy from the GaAs to oxygen molecules physisorbed on the surface causes the breakup of the oxygen and so enhances the reaction. This conclusion comes from comparison of our photoemission results for O2 and N2O exposures made under the same conditions, N2O being chosen since only 1.7 eV is needed to remove the oxygen atom as opposed to the 5.1eV required to break an O-O bond. Nitrous oxide, in contrast to O2, shows only slight photoenhancement and has a much lower activation energy for the dissociative sticking coefficient, demonstrating that removal of the dissociation of O2 as a reaction step also removes the major part of the activation energy barrier to oxygen chemisorption. Since N20 and photoenhanced O2 have similar kinetics, we conclude that the breakup of O2 is the reaction step accelerated by illumination. Another clue to the nature of the photoenhancement comes from our finding that both n- and p-type GaAs display similar O2 laser enhancement ratios. An estimate of the carrier concentrations at the surface predicts that electrons and holes are present in equal amounts at the surfaces of both doping types, however, so this result does not distinguish between single-carrier and recombination-related enhancement mechanisms.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 75: Symposium B – Photon, Beam, and Plasma Stimulated Chemical Processes at Surfaces , 1986 , 575
Copyright
Copyright © Materials Research Society 1987

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