First-principles investigation of a-line Shockley partial dislocations in wurtzite GaN: core reconstruction and electronic structure

Abstract

Αtomistic simulations based on density functional theory were performed to investigate Shockley partial dislocations, parallel to the <11–20> direction, in wurtzite gallium nitride. The cores of both 30° and 90° Shockley partial dislocations, their possible reconstructions and their electronic structures were analyzed and compared systematically. Shockley partial dislocations were found to have a variety of core structures while exhibiting different bonding states like: deformed Ga–N bonds, Ga–Ga and N–N homo-nuclear bonds, as well as Ga– and N–dangling bonds. We have demonstrated that the core reconstruction of these dislocations is not always energetically favourable in wurtzite GaN, as it is the case in elemental semiconductors. It results from interplay between the energy gain from eliminating dangling and forming homo-nuclear bonds and the energy excess from the induced strain of hetero-nuclear Ga–N bonds within the core. Depending on their core configurations, Shockley partial dislocations are expected to have different electronic behaviours in wurtzite GaN, as they can act either as sources of parasitic luminescence or non-radiative recombination centres, or give pathways to leakage currents. We have demonstrated that deep states associated with dislocations are not due to the dangling bonds, as generally believed, but rather to Ga–Ga bonds in their cores, and that N–N bonds do not lead to any gap states. These results are of high relevance as guidelines in defect engineering strategies aiming at producing dislocations with a particular electronic behaviour in wurtzite GaN.