The optical and carrier transport properties of In0.38GaAsNx/GaAs single-quantum-well diode laser structures of x ranging from 3% to 3.8% were investigated by temperature-dependent photo luminescence (PL) spectroscopy, photocurrent spectroscopy, differential absorption spectroscopy, and deep-level transient spectroscopy (DLTS). A carrier localized state of ∼ 12 meV activation energy and of a delocalization temperature at ∼ 150 K was observed by PL thermal quenching data. We also observed a Gaussian shape absorption edge of increasing absorption strength with the reverse bias in the photocurrent spectra. DLTS data show a hole trap of 0.34 eV activation energy possibly originating from the In0.38GaAsNx layer. © 2005 Elsevier B.V. All rights reserved.