A Study of Degradation in High Power Multi-Mode InGaAs-AlGaAs Strained Quantum Well Lasers as Pump Lasers
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1195-B01-06
A Study of Degradation in High Power Multi-Mode InGaAs-AlGaAs Strained Quantum Well Lasers as Pump Lasers Yongkun Sin, Nathan Presser, Neil Ives, and Steven C. Moss Electronics and Photonics Laboratory The Aerospace Corporation El Segundo, CA 90245 ABSTRACT Degradation processes in high power broad-area InGaAs-AlGaAs strained quantum well lasers were studied using electron beam-induced current (EBIC) techniques, time-resolved electroluminescence (TR-EL) techniques, and deep-level transient spectroscopy (DLTS). Accelerated lifetests of the broad-area lasers yielded catastrophic failures at the front facet and also in the bulk. EBIC was employed to study dark line defects generated in degraded lasers stressed under different test conditions. TR-EL was employed to study the intra-cavity intensity distribution in real time as devices were aged. DLTS was employed to study deep electron traps in both pristine and degraded laser diodes. Lastly, we present a possible scenario for the initiation of bulk degradation in the broad-area lasers. INTRODUCTION High power broad-area InGaAs-AlGaAs strained quantum well (QW) lasers with emission wavelengths at 915-980 nm are used as pump lasers to optically pump various fiber lasers and amplifiers [1, 2]. These applications, mainly developed for industrial uses, do not require stringent reliability from the pump lasers. Because these pump lasers have not been deployed in high reliability communications systems including potential satellite systems, careful study of reliability and degradation of these devices is needed. The maximum output powers of both single-mode and broad-area lasers are limited by catastrophic optical mirror damage. However, unlike 980 nm single-mode lasers where a single failure mode is typically observed due to good facet passivation along with optimized structural designs, broad-area lasers have shown at least two different failure modes including facet catastrophic optical damage (COD) and bulk failure. There have been extensive reports on facet COD, but very limited reports on bulk degradation although catastrophic bulk failure has been identified as the dominant failure mode in broad-area InGaAs-AlGaAs strained QW lasers [3]. For the present study, we investigated degradation processes in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers at ~975nm by performing accelerated lifetests of these devices and failure mode analysis (FMA) with various techniques including electron beam induced current (EBIC), time resolved electroluminescence (TR-EL), and deep level transient spectroscopy (DLTS). EXPERIMENTAL METHODS Laser diodes under study The laser diodes studied were broad-area lasers with windows formed in the backside n-metals, which allowed direct observation of spontaneous emission from the entire active layer. Windows were introduced using our newly developed angle polishing technique, which allowed us to selectively remove the backside metal except a ~100µm wide
metal strip left for wire bonds. More than sixty samples were prepared usi
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