Comparison of facet temperature and degradation of unpumped and passivated facets of Al-free 940-nm lasers using photoluminescence

Influences of facet degradation of Al-free InGaAsP-GaAs 940-nm laser diodes were studied at power densities well below catastrophic optical mirror damage level using photoluminescence (PL) during normal operation and after a rigorous burn-in procedure. The shift in the PL peak of the cladding layer of the device is used to calculate the temperature of the facet. Devices with different facet treatments: untreated electron beam evaporation, untreated ion beam deposition, unpumped and passivated facets were compared. The results indicate that the degradation of facet is more severe for untreated and unpumped facets as compared to passivated facets. The results were also compared with power measurements, which show that the drop in the power during the first 50 h of operation is nonexistent for passivated facet devices leading to the conclusion that photo-induced oxidation is the major cause of the degradation of the facet and thus oxide removal and surface passivation are crucial to make stable laser diodes.