Papers by Author: A.T. Blumenau

Abstract: Recently, the interaction of copper with dislocations in p-type Si/SiGe/Si structures has been investigated experimentally and a new dislocation related DLTS-level at Ev +0.32 eV was detected after intentional contamination with copper. To determine the origin of this newly detected level, in this work we present first density functional calculations of substitutional copper at 90◦ and 30◦ partial dislocations in silicon. Defect–dislocation binding energies are determined and electrical gap levels are calculated and compared with the experimental data. As a result, the observed level at Ev + 0.32 eV is tentatively assigned to the single acceptor level of substitutional copper at the dislocation.

Abstract: Under forward bias bipolar 4H- and 6H-SiC devices are known to degrade rapidly through stacking fault formation and expansion in the basal plane. It is believed that the ob- served rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations. This degradation phenomenon has generated considerable interest in the involved dislocations — in particular in their atomic and electronic structure, but also in the mechanisms of their glide motion. Fortunately, nowadays advances in computing power and in theoretical methodology allow the ab initio based modelling of some aspects of the problem. This paper therefore gives a brief review of recent activities in this field, and further discusses some general problems of ab initio based modelling of dislocations in compound semiconductors.

Abstract: 90 Shockley partial dislocations in GaN are investigated by first-principles calculations. This work is focussed on the electrical properties of dislocation cores, and on investigating the electrical fields around these defects. The band structure analysis shows that both the  and  core partials possess a midgap state. The -core dislocations give rise to a donor level Ev +0:87 eV that might explain the absorption peak at 2.4 eV revealed by energy loss spectroscopy measurements. The acceptor level Ev + 1:11 eV localized at the -core dislocations might contribute to the yellow luminescence. These dislocations experience a substantial charge polarization along the [0001] growth axis. In addition, we show that these dislocations tend to charge in a high stress field.