Intrinsic electronic structure of threading dislocations in GaN

In this paper we use multiple-scattering simulations in conjunction with experimental Z-contrast images and electron-energy-loss spectra to obtain a detailed analysis of the effect of the intrinsic structure of edge, screw, and mixed dislocations on the local density of unoccupied states in GaN. In particular, we show that the multiple scattering method is especially useful for examining dislocation cores where the bonding is significantly different at each atomic site in the structure. Furthermore, the analysis of the nitrogen K edge from intrinsic dislocations in GaN, i.e., stoichiometric cores with no dopants or vacancies, shows that the changes in the local electronic structure can be attributed to a change in the symmetry of the structure that does not result in readily identifiable states in the band gap. As such, the electrical activity at dislocations that limits the lifetime and performance of GaN devices appears to be related to the segregation of dopants, impurities or vacancies.