A detailed study on the optical quality of atmospheric pressure metalorganic vapor phase epitaxy grownGaAs(1−x)Nxepilayers (on GaAs substrates) in which the N incorporation is accomplished using dimethylhydrazine precursor is reported. We show here that the poor optical quality of these as-grown layers can be significantly improved by carefully planned post-growth heat treatments. Optical data are presented to demonstrate unambiguously that such treatments affect in no way the physical properties of these metastable layers (no phase separation) and that the improvement of their optical quality is closely connected to the incorporation behavior of N in this growth method. ©1998 American Institute of Physics.