Dresden 2003 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 29: GaN: Pr
äparation und Charakterisierung II
HL 29.1: Vortrag
Mittwoch, 26. März 2003, 14:30–14:45, BEY/118
EVIDENCE FOR A NEW DISLOCATION TYPE IN GaN. — •L. Lymperakis1, J. Neugebauer1, M. Albrecht2, T. Remmele2, and H.P. Strunk2 — 1Fritz-Haber-Institut der MPG, Berlin — 2Universität Erlangen-Nürnberg, Institut für Werkstoffwissenschaften, Lehrstuhl Mikrocharakterisierung, Erlangen
Previous theoretical studies [1] on various a-type dislocations (full core, Ga vacancy, N vacancy, open core) predicted all of them to be electrically active. In contrast a number of experimental studies find a-type dislocations to be not active. The question appears whether this is due to passivation of the dislocation core by H or due to a new type of dislocation core. Employing a multiscale approach that combines elasticity theory, Stillinger-Weber empirical potentials, and density-functional theory we identify a new type of a reconstructed dislocation core (having a 4-ring structure) which for intrinsic GaN is energetically more favorable than any of the previously considered structures. In contrast to those the core of the new structure is fully reconstructed, i.e. no broken bonds exist. An analysis of the electronic structure revealed that although the core is free of dangling bond states, the huge strain field around the dislocation core induces localized states near the conduction band. Further, based on the ab-initio calculated geometries, through focus high resolution transmission electron microscopy image simulations are performed by multi-slice calculations. A comparison with experimental images obtained for HVPE-grown GaN gives clear evidence for the existence of the reconstructed 4-core structure.
[1] A. Wright, U. Grossner, Appl. Phys. Lett. , 2751 (1998).