Regensburg 2000 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 3: Amorphe Halbleiter/Epitaxie
HL 3.2: Vortrag
Montag, 27. März 2000, 10:45–11:00, H13
Structural and electronic properties of fluorine impurities in tetrahedrally bonded amorphous carbon — •M. Amkreutz1, K. Kohary2, G. Jungnickel1, Th. Frauenheim1, and G. Seifert1 — 1Universität Paderborn, Fachbereich Theoretische Physik, 33098 Paderborn — 2Technical University of Budapest, Department of Theoretical Physics, H-1521 Budapest
We have applied the density-functional based tight-binding (DFTB) method to study the incorporation of fluorine into tetrahedral amorphous carbon (ta-C). Previous experimental findings in graphite intercalation compounds where F atoms seem to stimulate the formation of 4-fold coordinated sp3 hybridized carbon led us to investigate the influence of F dopants on the structural and electronic properties of the amorphous material. We support the experimental conclusion that fluorine stimulates sp3 bonding in graphite. By analyzing the carbon hybrids we deduce the analogous relationship between fluorine content and number of 4-fold coordinated carbon atoms for the ta-C. Here, we observe a competition of local structures where fluorine is truly covalently bonded to the carbon host network and configurations where fluorine traps an electron, becomes inert, and exists unbonded in microvoids. We discuss the implications for the bonding characteristics and the consequences for the electronic properties of the ta-C:F system. We present results from both static and molecular dynamics models and discuss the charge transfer effects between carbon and fluorine which appear to be important for the chemical bonding. For this, we take advantage of the recently developed self-consistent charge extension to the DFTB technique.