Formation Mechanism of Nanotubes in GaN

A formation mechanism for so-called nanotube defects in GaN is proposed. It is shown that two related types of defects are formed: nanotubes and pinholes. Both start with $\mathsf{V}$ shaped facets on $\{10\overline{1}1\}$ polar planes. Slow growth rate on these polar planes and impurity poisoning of growth steps are suggested as being responsible for initiation of these defects.