Characterisation of molecular nitrogen in ion-bombarded compound semiconductors by synchrotron-based absorption and emission spectroscopies

We have studied formation of molecular nitrogen under low-energy nitrogen bombardment in a range of compound semiconductors by synchrotron-based X-ray photoelectron spectroscopy (XPS) around N 1s core-level and near-edge X-ray absorption fine structure (NEXAFS) around N K-edge. We have found interstitial molecular nitrogen, N2, in all samples under consideration. The presence of N2 produces a sharp resonance in low-resolution NEXAFS spectra at around 400.8 eV, showing the characteristic vibrational fine structure in high-resolution measurements. At the same time, a new peak, shifted towards higher binding energies, emerges in all N 1s photoemission spectra. We have found a shift of 7.6 eV for In-based compounds and 6.7 eV for Ga-based compounds. Our results demonstrate that NEXAFS and core-level XPS are complementary techniques that form a powerful combination for studying molecular nitrogen in compound semiconductors, such as GaSb, InSb, GaAs, InN, GaN or ZnO.