Stoichiometric Defects in Silicon Carbide

Abstract

Defect structures showing odd-membered rings are known features of several tetrahedral semiconductors as well as carbon nanostructures; examples of them are bond defects in crystalline and amorphous silicon, Stone−Wales defects in fullerenes and carbon nanotubes, and the core structure of partial dislocations in some tetrahedral semiconductors. We investigate, using Density Functional Theory, two types of stoichiometry-conserving defects, which we call SCD and antiSCD and which are metastable structures presenting five- and seven-membered rings, both in the cubic and in the hexagonal 4H−SiC polytypes. We also investigate the annealing properties of the two mentioned variants and find that one of them (SCD) easily disappears, turning back to a normal site, while the other (antiSCD) transforms to an antisite pair, overcoming a barrier of 0.21 eV. The very short lifetimes at ambient conditions explain why those defects have not been observed up to now, but they suggest they should be observable at very low temperature, and we provide local vibrational modes to facilitate their identification.