Epitaxial GaAs1-xNx alloy layers, nominally 200-nm-thick, with x up to 0.0375 were grown on GaAs(001) at temperatures T, varying from 500 to 650 degreesC to investigate nitrogen incorporation and lattice parameter variations during organometallic vapor phase epitaxy from trimethylgallium, tertiarybutylarsine, and 1,1-dimethylhydrazine. Quantitative secondary ion mass spectrometry measurements (SIMS) indicate that N incorporation decreases systematically with increasing T, to become almost negligible at 650degreesC. All films are coherent with the substrate as judged by high-resolution x-ray reciprocal lattice mapping although atomic force microscopy and cross-sectional transmission electron microscopy reveal the presence of cracks in films with x > 0.02. High-resolution x-ray diffraction measurements combined with SIMS analyses indicate that the lattice constant decreases linearly with increasing x following closely the predictions of Vegard's rule for x<0.03. At higher concentrations, the lattice constant decreases more rapidly as a significant fraction of N atoms becomes incorporated in nonsubstitutional sites as demonstrated by nuclear reaction analysis. (C) 2004 American Vacuum Society.