Gradual degradation may be caused by (1) Electrostatic Discharge (ESD) damage experienced by the device, or (2) defects in the materials used in the laser diode or the fabrication process from which it is made, and from moisture ingression that can occur from inadequate hermetic. Among the limitations known from semiconductor lasers, catastrophic optical damage (COD) is perhaps the most spectacular power-limiting mechanism. Here, absorption and temperature build up in a positive feedback loop that eventually leads to material destruction. In that period, Technology and Reliability ran a furious race, with the latter continuously trying to discover the new failure mechanisms intrinsic to the new devices, to invent suitable techniques to detect them, to model their kinetics, to find any precursor able to early point out any risk. Table 1 summarizes common failure modes and mechanisms of LEDs and laser diode devices. Assessment and selection of manufacturers who adequately and consistently control their processes is important in eliminating these controllable defects. The degradation of laser diodes is a severe problem for the laser makers, but it is also a very relevant defect physics problem as it involves optical, mechanical and thermal issues.
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