GaP0.98N0.02 layers having a thickness from 75 nm to 600 nm are grown on GaP substrates by metalorganic vapor phase epitaxy. Back-reflection X-ray topographs made with a synchrotron radiation of the thick GaP0.98N0.02 layers reveal images of misfit dislocations. The critical thickness of the grown GaP0.98N0.02 layer on GaP substrate is evaluated from the topographs to be about 200 nm. The strain relaxation is also observed from high resolution X-ray diffraction curves. X-ray diffraction curves and atomic force microscopy studies indicate that the GaP0.98N0.02 layers with thickness smaller than 200 nm possess a very good crystal quality, an atomically smooth surface with a roughness less than 0.3 nm and a well-defined interface without misfit dislocations between the layer and the substrate. (C) 2013 Elsevier B. V. All rights reserved.