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(a) Layer scheme of the investigated structures A, B, and C. (b) Schematic of experimental setup (top view) and coordinate system. The thermocamera includes an imaging optics. (c) Thermal image of the aligned setup (side view). The grayscale image represents the emissivity contrast. The insets show front (left) and rear facets (right) as well as a side view (bottom) on an enlarged scale. Thermal flashes as observed during the step test are overlaid to the insets. Their amplitude is normalized.
[(a) and (b)] Data from a step test toward COD for a device of batch B: (a) Optical output within the control pulses applied after each primary pulse versus the current of the primary pulse. (b) Magnitudes of thermal flashes vs primary pulse current. (c) Spatial decay of a thermal flash amplitude along the laser axis (z) as observed from the front facet. are found as lower limit for the depth of focus assuming no absorption of the infrared light within the semiconductor structure. Scanning electron micrographs of typical front (d) and rear (e) facet damages. Notice that these damage pattern to be not dependent on the device batch.
(a) Thermal images from a device belonging to batch B with overlaid thermal flashes tracing the propagation of the damage front along the laser axis. The 19 images have been taken during 19 successive pulses each in duration. The grayscale image represents the emissivity contrast. On top a scheme depicts the structure including bond wiring. (b) Motion of the position (center of gravity) of the heated area vs current for three devices. (c) Propagation of the spot of Planck’s radiation within the emitter stripe (x-z plane, pinpoints the front facet) as reconstructed from thermal images taken from a front facet COD of a device belonging to batch B. The shaded region indicates a likely path of damage propagation.
Average data describing performance and COD behavior of 12 devices from 3 batches.
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