There is presently a great interest in dilute III-V nitrides. The investigation of defects in these materials is rather scarce and of importance, as the practical use of these materials relies on the control of the defects present. For this purpose, nitrogen-doped GaP and GaAs crystals have been investigated by Fourier transform spectroscopy. The local vibrational modes of carbon-nitrogen and boron-nitrogen complexes are identified. The carbon-nitrogen complexes sit in T-P or T-A, interstitial sites and are oriented along four-fold axes of the lattice. The local vibrational modes of the boron-nitrogen complex show unusual features: they are accompanied by sidebands and they show a strong stress-induced dichroism at low temperatures. A tentative model of the boron-nitrogen complex is proposed. (c) 2005 Elsevier B.V. All rights reserved.