Density-functional tight-binding calculations of electronic states associated with grain boundaries in GaN

The electronic structure of the $(3\overline{7}40)\phantom{\rule{0.3em}{0ex}}\ensuremath{\Sigma}=37\phantom{\rule{0.3em}{0ex}}(\ensuremath{\theta}=9.3\ifmmode^\circ\else\textdegree\fi{})$, $(3\overline{5}20)\phantom{\rule{0.3em}{0ex}}\ensuremath{\Sigma}=19\phantom{\rule{0.3em}{0ex}}(\ensuremath{\theta}=13.4\ifmmode^\circ\else\textdegree\fi{})$, and $(1\overline{3}20)\phantom{\rule{0.3em}{0ex}}\ensuremath{\Sigma}=7\phantom{\rule{0.3em}{0ex}}(\ensuremath{\theta}=21.6\ifmmode^\circ\else\textdegree\fi{})$ tilt grain boundaries has been investigated by means of atomic computer simulation within the density-functional-based tight-binding approach. Among the three possible atomic configurations of these boundaries, namely, the 5/7-, the 4-, and the 8 dislocation core interfaces, it is shown that the 4 or 8 interface introduces deep states in the very center and the upper half of the band gap whereas the 5/7 interface possesses only states close to the conduction band.

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