Nitrogen K-edge X-ray absorption measurements on N- and O-implanted GaN

Nitrogen K-edge X-ray absorption measurements are used to study the effect of N+ and O+ implantation in the microstructure of GaN. In the as-grown sample, the central N atom is four-fold coordinated with 3.35 Ga atoms at the expected distance of 1.93 Angstrom, and 0.65 displaced to a distance longer by about 0.33 Angstrom. This distortion in the nearest neighbor distances is attributed to thermal strain and/or to the presence of N vacancies. Implantation with either N or O ions enhances the distortion in the microstructure and the number of the displaced Ga atoms increases from 0.65 to 1. In addition to that, implantation causes a reduction in the nearest neighbor distances by about 2% and an increase in the Debye-Waller factors. Finally, implantation induces states in the gap that are detectable in the near edge X-ray absorption fine structure (NEXAFS) spectra, where they introduce a characteristic transition at about 1.4 eV below the absorption edge. (C) 1999 Elsevier Science B.V. All rights reserved.