The degradation of semiconductor light-emitting diodes, high-radiance lamps and lasers

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Abstract
Experimental results on LEDs show that a number of light-degrading mechanisms can operate which probably include migration of impurities or point defects. Dislocations when present in high densities also give rise to degradation in LEDs. Extrapolated lives to half intensity of between 105 and 107 h have been commonly projected for these devices, and this rather slow rate of degradation appears to have been achieved by minimizing impurity contamination, reducing strain and minimizing the dislocation density in the carrier recombination region. Relatively long lives have also been predicted for high-radiance, high-current-density lamps from thermally accelerated life-tests. Dark-spot and dark-line defects have been observed. In one case, the dark structure has been shown to result from the formation of tangles of dislocations generated during fabrication. High-current-density lamps which are free from dark structure also have projected lives of between 105 and 107 h. Generally, laser diodes can now be made which have lives in excess of 104 h. Details of the dark structure resulting from dislocations is reviewed and consideration is given to the remaining causes of degradation in lasers.