GaInNAsSb quantum wells with GaNAs barriers, grown via molecular beam epitaxy (MBE) on 100–oriented GaAs substrates at varying temperatures, were analyzed using photoluminescence (PL), high-resolution x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive spectrometry (EDS). Samples grown at 420 °C, 440 °C, and 470 °C were analyzed, as were two pieces of the 440 °C growth temperature sample that had been annealed at 740 °C and 820 °C. These measurements showed that the decrease in PL with higher growth temperatures was due to the onset of 3D growth and the nucleation of dislocations. The degradation associated with overannealing was likely due to dislocation nucleation. The poor PL associated with low growth temperatures was due to another mechanism, most likely arsenic anti-site defects. EDS measurements showed greater composition uniformity with lower growth temperatures, as expected, and also showed that there was no ordered indium-rich or indium-poor phase separation at any temperature. Phase separation upon annealing was not observed.