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We have used synchrotron-based near-edge x-ray absorption fine structure (NEXAFS) spectroscopy to study the electronic structure of nitrogen-related defects in several compound semiconductors, such as GaN, InN, GaSb and InSb. Several defect levels within the band gap or the conduction band were clearly resolved in NEXAFS spectra around the nitrogen K-edge. We attribute these levels to interstitial and antisite nitrogen. A sharp resonance above the conduction band minimum observed from all samples under consideration was attributed to molecular nitrogen, in full agreement with the vibrational fine structure of the N 1s→1Π* resonance in molecular nitrogen. The vibrational fine structure observed in compound semiconductors exhibits substantially larger lifetime linewidth Γ than in isolated molecular nitrogen. A clear correlation between Γ and the lattice constant of the host matrix has been found, indicating that the broadening of vibrational levels is governed by a finite probability of the electron to escape from the Π* orbital into the matrix. |