We investigate the effects of both nonradiative recombination centers and compositional inhomogeneity on low-temperature localization in GaInNAs quantum wells. With the introduction of antimony and a reduction of nitrogen plasma-related damage during growth, localization energies as low as 2.5 meV are reported for single quantum well samples with room temperature emission at 1.5 mu m. Moreover, low-temperature photoluminescence spectra revealed a broad, sub-band-gap luminescence peak that is ascribed to plasma-related defects. Deviation from the Varshni dependence of the band gap below 50 K was also observed and attributed to compositional inhomogeneity that localizes emission; however, no "S shape" was observed. Localization effects were found to depend upon the excitation density. (c) 2005 American Vacuum Society.