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 of
E
-gun deposited Al
2
O
3
applied 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 (Al
2
O
3
) 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.