Dresden 2006 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 5: SiC
HL 5.3: Vortrag
Montag, 27. März 2006, 12:45–13:00, BEY 154
Kinetic mechanisms for the deactivation of nitrogen — •Alexander Mattausch, Michel Bockstedte, and Oleg Pankratov — Theoretische Festkörperphysik, Staudtstr. 7/B2, 91058 Erlangen, Germany
Nitrogen is a common dopant in silicon carbide. It is known that nitrogen substitutes for carbon atoms. Yet surprisingly, recent experiments have shown [1] that the silicon co-implantation (which should support N incorporation on the C-sublattice) leads to a significant deactivation of nitrogen at high annealing temperatures. At the same time, the concentration of compensating centers decreases. Employing ab initio density functional theory calculations we investigate the interaction of the nitrogen dopants with self-interstitials and vacancy aggregates in 4H-SiC. We find that a silicon interstitial can kick-out the activated NC, since the emission of a nitrogen interstitial from the (N-Si)C complex is favoured over the silicon emission by 1 eV. The reaction of N with carbon interstitials leads to (CN)-complexes which possess deep levels. These defects have dissociation energies between 2.6 eV and 3.2 eV and thus are thermally stable. Yet, the formation of these complexes requires moderate temperatures and cannot be responsible for the high temperature annealing behaviour after silicon co-implantation. A possible alternative is the formation of the highly stable vacancy clusters (VC)n-VSi. Due to the high migration barrier of VC this process is possible only at high temperatures. These defects can trap nitrogen interstitials, finally leading to the electrically passive (NC)4-VSi complexes.
[1] F. Schmid and G. Pensl, Appl. Phys. Lett. 84, 3064 (2004).