Activation energy of degradation in GaAlAs double heterostructure laser diodes

Aging test of GaAlAs double heterostructure (DH) laser diodes is performed in the temperature range of 50–180 °C. In samples for the aging test, AuSn-alloy bonding solder is used and the facet coating with Al2O3 film is performed. Samples are operated in the light emitting diode (LED) mode with the application of the constant current of 4 kA/cm2 and 6 kA/cm2 at temperatures above 80 °C and in the automatic power control (APC) lasing mode with the constant optical power of 5 mW/facet at 50 and 70 °C. The activation energy is 0.5 eV obtained from the results of the LED mode operation at 4 kA/cm2. The parameter to evaluate the degradation is the current at which the optical power at 25 °C is 5 mW/facet. This parameter includes the deterioration of the external differencial efficiency. It is shown that the increasing rates of this parameter are almost the same at the same temperature between the LED mode operation at 4 kA/cm2 and 6 kA/cm2. The increasing rate is almost the same when samples are operated in the APC lasing mode. Twenty-three samples operated at 70 °C maintain the optical power of 5 mW/facet set initially over 5000 h. The averaged increasing rate of that parameter in these samples is 7.1×10−6/h. The activation energy of 0.5 eV is almost the same as that of GaAlAs DH LED’s which is 0.56 eV. It is presumed that point defects which disperse homogeneously cause the degradation of laser diodes and this degradation mode seemed to be the same as LED owing to the improvements against the facet degradation and the contact degradation.