We present the change in diffused scattering intensity and crystal truncation rod in X-ray reciprocal space mapping (RSM) of GaNxAs1-x grown by a radio frequency (RF) nitrogen plasma source in a solid source molecular beam epitaxy system. The RSM results are discussed in relation to variation in the low-temperature photoluminescence (PL) efficiency and peak energy. The X-ray RSM plots were recorded using a high-resolution triple-axis X-ray diffractometer on GaNAs samples annealed from 550 to 800degreesC. The RSM plots show higher diffused scattering around the GaNAs and GaAs (004) reflection point for the as-grown GaNxAs1-x sample with x = 1.3%, indicating a high incorporation rate of N atoms and N complexes as interstitials, compared to a 5 mum-thick unintentionally doped GaAs sample. A reduction in diffused scattering around the GaNxAs1-x and GaAs (004) Bragg reflection point was observed with sharp termination of the crystal surface in the sample annealed at similar to 700degreesC for 10min. This is in good agreement with the observed improved PL efficiency, due to annihilation of interstitial point defects. (C) 2002 Elsevier Science B.V. All rights reserved.