Dresden 2006 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 34: Impurities/Amorphous semiconductors

HL 34.1: Vortrag

Mittwoch, 29. März 2006, 17:15–17:30, BEY 154

Measurement of the spatial extension of defect states by probing vacancy interactions — •Philipp Ebert, Ansgar Laubsch, and Knut Urban — Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich

The spatial extension of localized electronic states of defects in semiconductors governs to a large degree the formation of defect bands and thus the properties of semiconductor materials. Unfortunately, the spatial extension of localized defect states is largely unknown. On the one hand theory suffers from the limited size of the supercells used, where states from neighboring defects overlap. On the other hand experiments mostly rely on STM images, where defect states can be directly imaged. However, the electric field between the tip and the sample induces an extensive band bending in semiconducting surfaces, which modifies the spatial extension of the imaged defect states. Here we domonstrate for P vacancies in InP(110) surfaces that the extension of the localized defect state in the band gap can be extracted from measuring the vacancy-vacancy interaction potentials. The interaction potentials are extracted from imaging only the position of the vacancies, which remain unaffected by the electric field of the tip. We find that surface vacancies exhibit a two-dimensional repulsive screened Coulomb interaction at high vacancy concentrations, due to the formation and partial population of a vacancy-related defect band in the band gap. In contrast at low vacancy concentration no two-dimensional screening occurs, since the vacancy states do not overlap. From this we extract that the localized P vacancy state in the band gap has a spatial extension larger that 4.1 nm in diameter.