Optoelectronic performance of gallium nitride devices: the role of tilt grain boundaries and point defects

The electronic structures of perfect tilt grain boundaries in the gallium nitride (GaN) and the interaction of point defects with their boundaries have been investigated. Our calculations suggest that among the three possible atomic configurations describing the perfect tilt grain boundaries, namely, the 5/7-interface, the 4-interface and the 8-interface, it was found that the 8-interface introduces deep states in the very center and the upper half of the band gap whereas the 5/7-interface possess only states close to the conduction band. The N-vacancy in the 8-interface introduces filled or empty electronic states inside the band gap. Such states may give rise to transition towards the valence band, which could be a candidate to account for the yellow luminescence (YL) in GaN. For the gallium or nitrogen interstitial in interaction with the GaN tilt grain boundaries, it was shown that while the Ga-interstitial introduces empty deep-states in the very center and filled shallow-states in the half bottom of the band gap, the N-interstitial gives only rise to shallow-states at the band edges. Given that for an electrically neutral boundary the deep states are unoccupied (deep acceptors), such defects may contribute to the YL.