The transient thermal characteristics related to catastrophic optical damage (COD) in high power AlGaAs/GaAs laser diodes (LDs) are studied experimentally by means of thermal infrared imaging, laser scanning confocal microscopy, and transient thermal technique. The transient thermal technique is based on the diode forward voltage method in which the structure function theory is applied to determine the component thermal resistance and temperature rise of the LDs. We have recorded the dynamics of COD process using thermal infrared camera. Two melting spots are observed in the output facet after COD which location exactly matches the position of the thermal flash from the thermal imaging and even the temperature of COD seed has a sudden increase of 32 K when the COD event occurs. Furthermore, we find that the thermal resistance from chip to In solder increases remarkably after COD, meanwhile the thermal resistance of solder and package does not change apparently. The results are attributed to the heat power dissipation increase originating from the enhancement of nonradiative recombination after COD under constant input electrical power.
The degradation of AlGaAs/GaAs laser diodes is studied in detail using laser scanning confocal microscopy, cathodoluminescence images, and x-ray diffraction (XRD) techniques. Our analysis has identified a degradation mechanism that results from the periodic distribution of the carrier density and the near-field intensity originating from periodic spatial hole burning. Based on the XRD measurements, we find that the epitaxial layer enters a polycrystalline phase during degradation due to the dark line defects, and the out-of-plane strain and in-plane compressive stress are induced by degradation.
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