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O: Fachverband Oberflächenphysik

O 27: Poster Session I (Methods: Scanning probe techniques; Methods: Atomic and electronic structure; Methods: Molecular simulations and statistical mechanics; Oxides and Insulators: Clean surfaces; Oxides and Insulators: Adsorption; Oxides and Insulators: Epitaxy and growth; Semiconductor substrates: Clean surfaces; Semiconductor substrates: Epitaxy and growth; Semiconductor substrates: Adsorption; Nano- optics of metallic and semiconducting nanostructures; Electronic structure; Methods: Electronic structure theory; Methods: other (experimental); Methods: other (theory); Solutions on surfaces; Epitaxial Graphene; Surface oder interface magnetism; Phase transitions; Time-resolved spectroscopies)

O 27.14: Poster

Dienstag, 24. März 2009, 18:30–21:00, P2

Scanning Tunneling Spectroscopy at the [110]-[110] Cleaved Edge of GaAs — S. Siewers, M. Wenderoth, L. Winking, •P. Kloth, and R. G. Ulbrich — IV. Phys. Inst. Georg-August-Universität Göttingen

We report the first cross-sectional scanning tunneling spectroscopy (STS) study of zincblende [110]-[110] cleaved edges with atomic resolution. The samples were prepared in-situ by a double cleavage procedure applied to 6 · 10¹⁸ cm⁻³ Si-doped GaAs in UHV. In edge-approaching scans and for positive sample bias we observed a monotonically decreasing tunnel current within a few tens of nm from the edge. For negative bias we found the onset of this decrease within a few nm from the edge, followed by a considerable increase directly at the edge. Comparing these observations with scans over charged defects embedded in plane surfaces, we conclude that the edge contains a negative line charge density. The data suggests that the observed effect is not simply caused by tip-induced band bending and screening of bulk states confined within the 90^∘-edge geometry. Spectroscopic measurements on edges support the concept of a negatively charged quasi-1d electronic state localized along the edge. It is laterally confined within ∼2 lattice constants and is clearly observed in the local density of states derived from the STS data. To estimate the absolute value of its charge density we simulated the shape and spatial extension of the screening cloud of a negative line charge located at the center of the "quarter-space" geometry. By adjusting this potential to the spectroscopic data we find a line charge density of ∼0.7 electrons per unit cell.