Deep-level transient spectra DLTS and photoresponsivity were measured for Ga0.90In0.10N0.033As0.967 /GaAs and Ga0.96In0.04N0.028As0.967Sb0.005 /GaAs p-i-n photodetector structures. The GaInNAs and GaInNAsSb layers were grown closely lattice matched to GaAs substrate at 460 °C using molecular beam epitaxy. Two hole-trap levels were observed in the DLTS spectra of the GaInNAs sample with activation energies of 0.152 and 0.400 eV labeled as H-1 and H-2 peak, respectively . The lower activation energy is believed to be associated with nitrogen-related defects and the higher activation energy is associated with arsenic antisite defects AsGa . Following the incorporation of Sb into GaInNAs, the H-1 peak vanished from the DLTS spectra of the GaInNAsSb sample, and the AsGa defect-related DLTS signal was significantly reduced. Analysis of the DLTS data also showed that the trap concentration related to AsGa was reduced from 2.15 1015 to 2.58 1014 cm−3. The DLTS results are in good agreement with the photoresponsivity results, in which the GaInNAsSb sample showed 10 higher photoresponse compared to the GaInNAs sample. This indicates the incorporation of Sb into GaInNAs has effectively improved the p-i-n photodetector device performance.