The effect of sputtered-SiO2facet coating films on the suppression of self-sustained pulsations in the output of (GaAl)As double-heterostructure lasers during CW operation

In order to clarify the cause of self-sustained pulsation (SSP) associated with degradation, both channeled-substrate-planar and new buried-heterostructure lasers were life tested under various conditions. Surface layers at the laser mirrors, which probably included large nonradiative recombination centers, were etched off to a depth of 200-500 Å by Ar+ ion etching, then sputtered-SiO2films were deposited on both mirrors without the laser chips being removed from the apparatus. Optical microscope observation for the mirrors of the aged lasers and electroluminescent patterns observed in the active layers revealed that the SSP was caused by a mechanism closely related to optically induced faults, such as oriented dark line defects, which formed a saturable absorption region in the interior of the laser near the mirror. Facet coating films formed with the above process were found to be quite helpful in suppressing the occurrence of SSP provided that power densities were kept less than the moderately high value of 0.6 MW/cm²(∼15 mW/facet).