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The reliability of high radiance InGaAsP/InP DH LED's operating in the m wavelength and the defect structures observed in this quaternary alloy have been presented. Threading dislocations and misfit dislocations do not act as strong nonradiative recombination centers, in contrast with the case in GaAs or GaAlAs optical devices. Dark-spot defects (DSD's) were sometimes generated in the emitting area during aging at elevated temperatures. These defects were analyzed microscopically using a transmission electron microscope and were identified as precipitates. To investigate the homogeneous degradation, accelerated aging at the ambient temperatures of 20, 60, 120, 170, 200, and 230°C has been carried out for over 15 000 h at the current density of 8 kA/cm ² using LED's without dark structures. The degradation rates were statistically calculated by assuming the normal distribution. The mean values …