Dislocations in hexagonal and cubic GaN

The structure and electronic activity of several types of dislocations in b oth hexagonal and cubic GaN are calculated using first-principles methods. Most of the stoichiometric dislocations investigated in hexagonal GaN do no t induce deep acceptor states and thus cannot be responsible for the yellow luminescence. However, it is shown that electrically active point defects, in particular gallium vacancies and oxygen-related defect complexes, can h e trapped at the stress field of the dislocations and may be responsible fo r this luminescence. For cubic GaN, we find the ideal stoichiometric 60 deg rees dislocation to be electrically active and the glide set to be more sta ble than the shuffle. The dissociation of the latter is considered.