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We report on an extensive study of the defect structure associated with catastrophic failure of GaAs-based 980 nm pump lasers. Electron beam induced current (EBIC) analysis shows that catastrophic optical damage (COD) is characterized by the introduction of high densities of extended defects in the optical cavity of the laser, in the vicinity of the output facet. The heterostructure comprising the active region of the device is interdiffused in a spherical region surrounding the region of highest defect density. In some regions, melting of the laser cavity is observed. A “fast capture” laser degradation analysis demonstrates that the COD damage initiates at the laser facet, and propagates back along the cavity with continued device stressing. COD failure under pulsed operation results in a dramatically altered defect distribution consisting of periodic arrays of dislocation tangles along the laser cavity. Successive pulses following the initial failure event result in the formation of fresh defect “packets” which are separated from the damaged region generated due to the preceding pulse by a volume of relatively defect free material. The periodicity of these defective packets is related to the magnitude of the drive current pulse at the time of failure. Following the description of the defect distribution obtained using EBIC, we employed site-specific transmission electron microscope sectioning methods to form a detailed description of the structural modifications that the device undergoes at the onset of failure.

Measurements of longitudinal variation in critical laser parameters such as gain and carrier concentration are invaluable in understanding and diagnosing device performance and failure mechanisms. However, traditional frontfacet measurements cannot reveal the variation of these parameters along the length of the laser. Other methods require physical modifications to the laser itself, such as the fabrication of a top window, and are thus invasive.We describe a new experimental technique based on analysis of side spontaneous emission. A tapered optical fiber translated along the side of the laser using a micropositioner collects spontaneous emission from the active region, allowing spatially-resolved gain and carrier concentration measurements to be made. Such measurements can be used to track the evolution of dark lines caused by defects where non-radiative recombination is dominant.We applied this method to a 980nm high power laser with an In02Ga8As, 80 A SQW and facets of 90%/1O% reflectivity. It was predicted through a one-dimensional rate equation model that the carrier concentration would increase near the high-reflectivity mirror, due to lower optical field intensities. Using the bimolecular recombination equation to determine the carrier density, this expectation was confirmed. The peak modal gain also increased with proximity to the high-reflectivity mirror, and modulations in the gain peak profile attributed to spatial hole burning were observed.

Longitudinal variations of photon and carrier density along the length of a Fabry–Perot quantum well laser are simulated and compared to experimental carrier density measurements performed using a side spontaneous emission scanning technique. Both simulation and measurement demonstrate the existence of carrier nonpinning along the cavity of the laser, with increasing carrier density from the low reflectivity facet toward the high reflectivity facet. Measured carrier densities increased monotonically above their threshold value with injection current, at all points along the laser, seemingly contradicting the condition of net round-trip gain pinning at threshold. This behavior is attributed to current spreading into the low-gain regions aside the active region causing a current-dependent increase in spontaneous emission, and thus an apparent increase in measured active region carrier density. Periodic spatial modulation of the carrier density profile, consistent with the hypothesis of beam steering induced by beating and locked lateral modes, was also observed.