Temperature field determination of InGaAsP/InP lasers by photothermal microscopy: Evidence for weak nonradiative processes at the facets

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Abstract
Photothermal microscopy was used for absolute temperature determination of InGaAsP/InP lasers. High modulation frequencies were employed in order to improve spatial contrast. The strong thermal mismatch between InGaAsP and InP induces a heat confinement in the active region as shown experimentally and confirmed by finite element calculations. Facet temperature was found to be 10 K/mW for a 2-μm-wide active layer, which is low compared to those reported for GaAlAs/GaAs and GaInP. Moreover, measurements along the cavity do not show differences in temperature when approaching the facets. Both results indicate a weak nonradiative recombination process at the facets, in agreement with the higher mirror reliability of this type of laser.