Strain and temperature distribution in broad-area high-power laser diodes under operation determined by high resolution X-ray diffraction and topography

Broad-area lasers were investigated by high resolution X-ray diffraction (HRXRD) and topography, before and during laser operation. Rocking curves were taken at different positions of the 150 μm wide and 2 mm long laser stripe, using high-precision motorized slits with a spatial resolution of 40×40 μm². From the series of rocking curves recorded at different lateral positions and driving currents, the curvature and temperature profiles along the stripe could be estimated for different driving currents. X-ray topographs revealed regions with higher strain compared to the surrounding area. At lateral positions within the stripe, where the highest temperature was determined by HRXRD, regions of dark contrasts, indicating defects, were detected by cathodoluminescence. Transmission electron microscopy revealed that the highly strained regions act as sinks for point defects, since no dislocations or dislocation loops were detected. Thus, a clear correlation between temperature rise, high local strain and defect formation was found.