GaAsN/GaAs and GaInAsN/GaAs epitaxial layers, with band gap wavelengths as long as 1.25 and 1.3 μm, respectively have been successfully grown using triethylgallium, trimethylindium, arsine and dimethylhydrazine. The dependence of nitrogen incorporation on growth temperature and In content has been determined. The band gap energy was lower than that predicted by theory, possibly due to short-range order. The intensity of the room temperature (RT) photoluminescence (PL) emission from as-grown GaAsN layers was found to decrease with increasing N content. The PL intensity of GaAsN layers with high N content increased upon annealing in nitrogen. The N content of GaAsN layers was unaffected by annealing at 650°C for 30 min. Phase separation has been observed in Ga 0.912In 0.088As 0.958N 0.042 but not in Ga 0.927In 0.073As 0.97N 0.03. No long-range order was seen in GaAsN or GaInAsN layers. No RTPL emission was observed in as-grown GaInAsN layers. Annealing these GaInAsN samples at 600–650°C for 10–30 min resulted in PL emission at wavelengths as long as 1.35 μm and a slight decrease in N content. Ga 0.7In 0.3As 1− x N x /GaAs quantum wells, with emission wavelengths as long as 1.3 μm, have been grown. The RTPL intensity of the quantum wells was found to decrease greatly for wavelengths greater than 1.2 μm. Upon annealing the quantum wells at 600°C the emission wavelength decreased and the intensity increased substantially for wells with initial emission wavelengths greater than 1.2 μm.