The difference in N concentrations in GaPN layers grown simultaneously on Si and GaP substrates is investigated. The N concentration was estimated by X-ray diffraction and photoluminescence (PL). For all sample pairs, the N concentration in the GaPN layer on the Si substrate was about 1% greater than that in the GaPN layer on the GaP substrate. It is conjectured that the misfit strain influences the incorporation of N atoms in GaPN layers. We also investigate the difference in PL spectra of GaPN layers having approximately the same N concentration. It was found that the deep-level emission from GaPN layers on a Si substrate were remarkably weak compared with that from GaPN layers on a GaP substrate. (c) 2006 Elsevier B.V. All rights reserved.