Both broad-area and single-mode strained InGaAs-AlGaAs single quantum well (QW) lasers are indispensable components for both terrestrial and space satellite communications systems due to their excellent power and efficiency characteristics. However, their degradation mode (catastrophic and sudden degradation) due to catastrophic optical damage (COD) is a major concern especially for space applications, since COD-prone lasers typically show no obvious precursor signature of failure. Furthermore, as our group first reported in 2009, these lasers predominantly degrade by a new failure mode (bulk failure) due to catastrophic optical bulk damage (COBD) unlike AlGaAs QW lasers that degrade by a well-known failure mode (facet failure) due to catastrophic optical mirror damage (COMD). Unlike COMD, there have been limited reports on root causes of COBD. In addition, none of decades-long studies of reliability and degradation processes in (Al)GaAs or InGaAs QW lasers by many groups have yielded a reliability model based on the physics of failure. As part of our efforts to develop a physics of failure-based reliability model of InGaAs-AlGaAs strained QW lasers, we continued our investigation by performing short-term and long-term lifetests, failure mode analyses, and root causes investigations using various destructive and non-destructive techniques. All of broad-area and single-mode lasers that we tested degraded by COBD. We employed electron beam induced current (EBIC) techniques to study formation of dark line defects (DLDs) of lasers stressed under different test conditions and time-resolved electroluminescence (TR-EL) techniques to study the dependence of DLD propagation on electrical-thermal stresses via recombination enhanced defect reaction. Also, we employed high-resolution TEM and deep level transient spectroscopy (DLTS) techniques to study extended defects and point defects (and electron traps), respectively. Finally, we report on reliability model parameters obtained from our physics of failure investigation and compare them with those extracted using an empirical model.
High-power laser manufacturers often perform accelerated multi-cell life-tests by applying significant amounts of stresses to lasers to generate failures in relatively short test durations and then use an empirical model to estimate lifetimes of the lasers. A drawback of this approach is overestimation of lifetimes at usage conditions due to the lack of failures generated under intermediate and low stress conditions. Many groups have studied reliability and degradation processes in GaAs-based lasers, but none of these studies have yielded a reliability model based on physics of failure. The lack of such model is a concern for space applications where complete understanding of degradation mechanisms is necessary. Furthermore, our group reported a new failure mode in multi-mode and single-mode InGaAs-AlGaAs strained QW lasers in 2009 and 2016, respectively. Our group also reported in 2017 that bulk failure due to catastrophic optical bulk damage (COBD) is the dominant failure mode of both SM and MM lasers. For the present study, we performed physics of failure (PoF) investigation to develop a PoF-based reliability model. Our physics of failure investigation consisted of (i) a series of long-term and short-term life-tests that exclusively generated COBD failures and (ii) destructive and non-destructive failure analyses using electron beam induced current, time-resolved electroluminescence, time-resolved photoluminescence, focused ion beam, highresolution TEM, and deep level transient spectroscopy.
While various layer schemes have been developed to protect thin film silver mirrors from tarnish and corrosion, the mechanisms by which these protective layers improve mirror durability are not fully understood. Mixed flowing gas exposure of plasma beam sputtered silver mirrors was used to investigate how the composition of the very thin adhesion layer changes the mechanism of corrosion feature growth. Two model mirror coatings were analyzed in which the composition of the base layer below the silver and the adhesion layer above were varied. Optical measurements and microscopy, SEM, TEM, and EDS were used to characterize the compositional and chemical effects at the layer interfaces. Large circular corrosion features formed along the silver-chromium interfaces; the addition of nickel to the layers on either side of the silver limited the growth of these features, but resulted in the corrosive attack of the silver itself.
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