Defects on GaAs Surfaces

In order to determine the structural properties of defects on semiconductor surfaces using STM, it is crucial to properly interpret the STM images using, for example, state-of-art first principles calculations. The case considered here in the above figures (click on small figures above to see full-size versions) is As vacancies on the GaAs(110) surface. STM images were generated using ab-initio wavefunctions and supercells, which probe the isosurface of the wavefunctions squared over a given energy window. The two figures here were calculated with a negative sample bias of about 2 eV to reveal states associated with surface As atoms. They show, on the appearance, that surface As atoms near the vacancy are displaced towards the underlying bulk. In calculations with large enough surface supercells (see the 2nd figure), significant As displacements in the STM images due to As vacancy were found while in fact the vacancy causes little As atomic motion. Discrepancies between the actual atomic positions and those inferred from the STM images for Ga atoms are even more pronounced. A detailed analysis explaining this paradox is the subject of the reference below.

Selected References

  1. S. B. Zhang and A. Zunger, Phys. Rev. Lett., 77, 119 (1996).

Other References

For a listing of all SST references on the topic "Clean Semiconductor Surfaces and Surface Steps", click on the "Get References" button below.

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