Local electronic structure of threading screw dislocation in wurtzite GaN

Abstract

The atomic and electronic structure of the full-core threading screw dislocation in wurzite GaN has been investigated using a self-consistent density-functional tight-binding calculation. It is shown that the atoms are severely strained in a hexagonal atomic core, and an extra charge transfer of 0.12 e occurs at the core atoms from Ga to N, in addition to the typical charge transfer of 0.56 e for bulk GaN. Filled and unfilled gap states are found to be spread over the entire band gap. The p states of the core N-atom mostly contribute to the tail states of valence and conduction bands, whereas the deep levels are heavily localized at the Ga and N core atoms. The coexistence of acceptor and donor gap states in the vicinity of the screw dislocations could be an origin of the leakage currents observed in GaN-based devices.