GaNAs(Sb) layers were grown by solid-source molecular-beam epitaxy utilizing a radio frequency (rf) nitrogen plasma source. The samples contained less nitrogen and antimony (0.5%-0.8% N and ≤2% Sb) than in previous studies and were examined for their optical and electronic properties and any interactions between the elements. Secondary-ion-mass spectrometry, high-resolution x-ray diffraction, electroreflectance (ER) spectroscopy, and photoluminescence (PL) measurements were used to study those properties. We found that the addition of small amounts of antimony enhanced nitrogen incorporation into GaAs, similar to other studies that used 5-15× the mole fraction of antimony. The nitrogen concentration increased with increasing antimony flux. PL measurements indicated an improvement in optical quality with increasing nitrogen and antimony concentrations-contrary to the belief that adding more nitrogen necessarily degrades material quality. We collected and simulated ER spectra to examine the general band properties of the layers. Isoelectronic codoping can explain the improved quality when antimony is added to GaNAs. The improvement in GaNAs with small amounts of antimony holds great promise for improving strain-compensated GaInNAs (Sb) GaNAs devices.