Point defects in gallium nitride: X-ray absorption measurements and multiple scattering simulations

We have studied the formation of nitrogen-related point defects in gallium nitride (GaN) using near-edge x-ray absorption fine-structure (NEXAFS) spectroscopy and ab initio FEFF calculations. The presence of several point defects, created within the GaN matrix by low-energy ion-bombardment, has been detected by NEXAFS measurements around N K-edge. FEFF simulations that take into account the formation of nitrogen antisites, interstitials, and vacancies around absorbing nitrogen atoms are consistent with NEXAFS results. The position of energy levels created by these defects within the energy gap of GaN, obtained by both NEXAFS measurements and FEFF simulations, are in good agreement with theoretical predictions.