N – K edge NEXAFS study of the defects induced by indium implantation in GaN

Abstract

N – K edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy is applied in order to determine implantation-induced changes in the electronic structure of GaN. The samples were implanted with 700 keV In ions and fluencies in the range 5×1013 – 1 × 1016 ions/cm2. The NEXAFS results are discussed in combination with Rutherford backscattering (RBS) characterization which assesses the implantation induced damage. The main implantation effects on the NEXAFS spectra are: (a) a fluence-dependent broadening of the NEXAFS peaks, (b) emergence of a pre-edge shoulder (RL1) that is attributed to N split-interstitials and (c) appearance of a post-edge sharp peak (RL2) that is attributed to molecular N2 trapped in the GaN matrix. The RL2 is characterized by fine structure due to vibronic transitions that result from a change of the vibrational quantum number along with the electronic transition. The concentration of the interstitials and the N2 molecules as well as the width of the NEXAFS peaks, have a sigmoidal dependence on the logarithm of the ion fluence, following the behaviour of the defect concentration deduced from the RBS measurements.