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J. Phys.: Condens. Matt. 12 (2000) pp. L489-L496

Nature of Friedel Oscillations around Si dopants in the GaAs(110) accumulation layer

J.E. Inglesfield

Department of Physics and Astronomy, University of Wales Cardiff, P.O. Box 913, Cardiff, CF2 3YB, United Kingdom

M.H. Boon

Institute for Theoretical Physics, University of Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen, Netherlands

S. Crampin

Department of Physics, University of Bath, BA2 7AY, United Kingdom

Abstract
The screening of sub-surface Si impurities in an accumulation layer at the GaAs(110) surface is calculated. Such an accumulation layer can be induced by a scanning tunneling microscope tip, and surface Friedel oscillations have been imaged around the Si dopants. This study uses the effective mass approximation to describe the electrons in the GaAs conduction band, and a fitted model potential for the impurity. Two-dimensional effects dominate, with a doubly occupied bound state pulled off the lowest sub-band by the impurity, and a depletion of one electron in the conduction states. The bound state gives a large central peak in the surface induced charge, with the Friedel oscillations coming from the change in the conduction states. To explain the amplitude of the observed oscillations, it is necessary to reduce the tunneling contribution from the bound state.