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Accelerated facet erosion formation and degradation of (Al, Ga)As double-heterostructure lasers

Beyond an initially occurring, temporally saturable mode of degradation, we demonstrate that clearly existing facet erosion does not cause degradation in (Al,Ga)As double-heterostructure proton-delineated stripe-geometry lasers with unprotected facets operated in a room-temperature (22°C) laboratory ambient [∼ 25 percent relative humidity (RH)] in times ∼3000 h and for power outputs ≈ 3 mW/ facet. Contrary claims relating facet erosion to long-term degradation are explained as actually being based upon observations of the initial saturable mode made under circumstances in which short and long term effects were not easily distinguished. A clear demonstration of a long-term facet erosion mode of degradation was produced by aging devices in a 70°C 85 percent RH environment. This elevated temperature ambient rich in oxygen and water vapor promoted a facet erosion which severely degraded laser performance. The observed significant increases in the operating current, required to maintain 3 mW/facet outputs, caused by both altered mirror reflectivities, in accord with theoretical expectations, and associated beam steering, could be substantially suppressed by half-wavelength "quick" coatings ofE-gun deposited Al2O3applied to the laser facets soon after cleaving. The aging results for the ambients examined suggest that alterations of the temperature and oxidant concentration in the aging environment should permit a characterization of the facet erosion mode of degradation, and a determination of the extent to which a real operating ambient must be oxidant or contamination free in order to realize the million hour lifetimes which have been predicted for room-temperature operation of these lasers. An alternative approach to facet protection, namely, a dielectric film (Al2O3) deposition, has been shown to be quite promising in an extreme example of a hostile environment (70°C 85 percent RH). The coating approach is stressed because it is highly desirable to coat lasers for reasons (reviewed herein) other than the prevention of facet erosion.