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STUDY OF MECHANISMS RESPONSIBLE FOR THE EFFICIENCY DEGRADATION OF THE III-NITRIDES LIGHT EMITTING DIODES

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The results for external quantum efficiency degradation of two types of light emitting diodes based on III-nitrides: blue and ultraviolet ones are presented. Existing mechanisms proposed for the degradation are considered briefly. Applying several techniques for studying the light emitting diodes at various stages of the aging test gives the possibility to reveal a new mechanism of defects formations with a help of multi-phonon recombination of carriers in an extended defects system and in local regions of random alloy fluctuations. These techniques include analysis of current voltage characteristics evolution at V<2V, the low frequency noise methods, and infrared microscopy. The multi-phonon recombination of carriers is accomplished by generation of native defects, in particular, In- or Ga-atoms and their migration. These processes lead to modification of the extended defects system properties and local composition of InGaN alloys in several regions that result in decreasing of the carriers participating in a radiative recombination and degradation of the external quantum efficiency. It was demonstrated that this mechanism of the defects formation can be responsible for the degradation of the blue and ultraviolet light emitting diodes. The mechanism can explain non monotonic dependence of the degradation process during the aging test, catastrophic failures of the light emitting diodes and low lifetime of the ultraviolet light emitting diodes. 

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