This paper reviews recent experimental progress in the investigation of nitrogen in GaAs and
GaAs-based dilute nitrides by Fourier transform infrared absorption spectroscopy. Isolated
substitutional nitrogen on the anion site gives rise to a local vibrational mode at a wavenumber of
472 cm−1, which can be detected at low temperatures as a sharp absorption band. Based on a
comparison with secondary ion mass spectroscopy and x-ray diffraction analysis, a calibration
factor is derived for the integrated absorption of the band. Quantitative determination of
substitutional nitrogen is possible in epitaxial layers of only 10 nm thickness. The influence
of indium–nitrogen bonding on the local mode frequency is discussed. A mode at
490 cm−1 is tentatively
attributed to the InGa3N
configuration. An additional local vibrational mode occurs at
638 cm−1. A valence-force model is presented, which reproduces quantitatively the experimentally
observed host-isotope fine structure. The results are consistent with an assignment to a
nitrogen–gallium vacancy complex.