Catastrophic degradation in high-power InGaAs ...

Catastrophic Degradation in High Power InGaAs-AlGaAs Strained Quantum Well Lasers and InAs-GaAs Quantum Dot Lasers Yongkun Sin*, Stephen LaLumondiere, Brendan Foran, Neil Ives, Nathan Presser, William Lotshaw, and Steven C. Moss Electronics and Photonics Laboratory The Aerospace Corporation El Segundo, CA 90245-4691 ABSTRACT Reliability and degradation processes in broad-area InGaAs-AlGaAs strained quantum well (QW) lasers are under investigation because these lasers are indispensible as pump lasers for fiber lasers and amplifiers that have found an increasing number of industrial applications in recent years. Extensive efforts by a number of groups to develop InAs-GaAs quantum dot (QD) lasers have recently led to significant improvement in performance characteristics, but due to a short history of commercialization, high power QD lasers lacks studies in reliability and degradation processes. For the present study, we investigated reliability and degradation processes in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers as well as in MBE-grown broad-area InAs-GaAs QD lasers using various failure mode analysis (FMA) techniques. Dots for the QD lasers were formed via a self-assembly process during MBE growth. We employed two different methods to degrade lasers during accelerated life-testing: commercial lifetester and our newly developed time-resolved electroluminescence (TR-EL) set-up. Our TR-EL set-up allows us to observe formation of a hot spot and subsequent formation and progression of dark spots and dark lines through windowed n-contacts during entire accelerated life-tests. Deep level transient spectroscopy (DLTS) and time resolved photoluminescence (TR-PL) techniques were employed to study trap characteristics and carrier dynamics in pre- and post-stressed QW and QD lasers to identify the root causes of catastrophic degradation processes in these lasers. We also employed electron beam induced current (EBIC), focused ion beam (FIB), and high resolution TEM to study dark line defects and crystal defects in post-aged QW and QD lasers at different stages of degradation. Keywords: High power lasers, broad area lasers, strained QW lasers, QD lasers, reliability, degradation mechanisms 1. INTRODUCTION High power broad-area lasers have attracted an increasing number of applications as pump lasers for solid-state lasers (λL= 808 nm) and for fiber lasers and amplifiers (λL= 915 - 980 nm). Although 915 - 980 nm broad-area lasers have a relatively short history of development compared to 808 nm broad area lasers, the broad-area lasers based on strained InGaAs-AlGaAs single quantum well (QW) heterostructures have recently shown remarkable output powers of over 20W from single emitters with 100 µm wide stripes [1-5]. This achievement has been made possible because (i) a number of groups have investigated the root causes of facet COD or catastrophic optical mirror damage (COMD) in GaAs-based lasers over the decades and successfully developed techniques including facet passivation to significantly increase a threshold for COMD and (ii) optical power density causing COMD at the facet of InGaAs-AlGaAs QW lasers is higher than (Al)GaAs QW lasers due to a low surface recombination velocity of InGaAs-AlGaAs materials systems. However, 915 - 980 nm multi-mode pump lasers still lack in-depth studies on their failure modes and degradation mechanisms mainly because their main applications have been industrial uses as pump lasers for Er-Yb co-doped fiber amplifiers. Recently, these lasers have been considered for high reliability applications including space satellite systems. Only a few groups have reported failure modes in 915 – 980 nm lasers [6, 7] including our group that reported failure mode analysis on these lasers using electron beam-induced current (EBIC) and high-resolution transmission electron microscopy (HR-TEM) techniques [8]. Facet COD, which typically limits maximum output power obtainable from GaAs-based lasers, has been known to be the dominant failure mode of these lasers since Henry, et al. reported in 1979 [9] that temperature rise at the facet due to presence of carriers generated by optical absorption of lasing photons and surface recombination could eventually lead to melting of facets via thermal runaway. ______________________________________________________________________ *[email protected]; phone (310) 336-1734; fax (310) 563-5755

Novel In-Plane Semiconductor Lasers XII, edited by Alexey A. Belyanin, Peter M. Smowton, Proc. of SPIE Vol. 8640, 86401G · © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2006624

Proc. of SPIE Vol. 8640 86401G-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/26/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

In 2009, tw wo groups rep ported a new failure f mode in i InGaAs-AlG GaAs strained QW lasers, bbulk COD or C COBD (catastroph hic optical bullk damage) [10, 11]. How wever, the roott causes of thhis failure modde are still noot well understood d and its impacct on long-term m reliability is a major concerrn especially foor space appliccations. Recenttly, we reported ou ur results of faailure mode in nvestigation ussing the time-rresolved electrooluminescencee (TR-EL) techhnique [12]. This technique mad de it possible to o directly obseerve the intra-ccavity optical inntensity distribbution in real ttime in broad-areaa lasers. In thee present study y, we further investigate i deggradation mechhanisms responsible for COBD in multi-mode InGaAs-AlG GaAs strained QW lasers. Various V destruuctive and nonndestructive faailure mode annalysis (FMA) techniques were employed e to in nvestigate thesee lasers at diffeerent stages of degradation. Inn addition, exttensive efforts by a number of groups g to develop high pow wer InAs-GaAss quantum dott (QD) lasers have recently led to significant improvementss in performancce characteristics, but due to a short historyy of commerciaalization, high power QD lasers significantly lacks studies in reliability and degradattion processess. We investiggated reliabilitty and degradation processes in MBE-grown broad-area b InA As-GaAs QD laasers using variious FMA techhniques. 2. EXPERIM MENTAL ME ETHODS We studieed MOCVD-grrown broad-arrea strained-laayer InGaAs-A AlGaAs singlee QW lasers lasing at ~975 nm, consisting of an InGaAs graded index separate con nfinement heteerostructure (G GRIN SCH) ssandwiched beetween AlGaAs clladding layers. These lasers had h a 100 μm wide w waveguidde and ~ 1.5 − 2 mm long cavvity. We also sstudied MBE-grow wn broad-area InAs-GaAs qu uantum dot (QD D) lasers lasingg at ~1150 nm m. These laserss had a 200 μm m wide waveguidee and ~ 3.6 mm m long cavity. Both strained QW lasers andd QD lasers thhat we studied were window lasers having an opening formeed in the backsside n-metal. This T configurattion is attractivve because it aallows us to peerform time-resolv ved electrolum minescence (TR R-EL) by directtly observing sspontaneous em mission from thhe entire activee layer or intra-cavity optical in ntensity distribu ution through the window. W Windows weree introduced too strained QW lasers during bacckside metallizzation process, whereas wind dows were intrroduced to QD D lasers using our angle pollishing technique. We were able to introduce windows w to C-m mounted laser ddiode chips byy selectively removing the baackside n-metal ex xcept an approx ximately 100 μm μ wide metal strip for wire bbonds as show wn in Figure 1. Facets of broaad-area laser diodees, mounted on n standard C-m mounts in p-sidee down configuuration, were ppassivated and then AR-HR ccoated. Note that the t optical inteensity distributiion in the activ ve layer of the 975 – 1150 nm m laser diodes was easily observed through thee ~120 μm thicck GaAs substrrate because it was transparennt at these lasinng wavelengthhs.

Rear Facet F

Window

N N-Metal

Front Facett

Figuree 1. Windowed d broad-area lasser on C-mounnt.


Typical strained QW lasers showed a laser threshold of ~300mA and slope efficiency of ~0.9W/A. The external differential quantum efficiency was ~0.7W/A. The characteristic temperature (or T0) was ~130K between 25 and 85°C. Typical QD lasers showed a laser threshold of ~900mA and slope efficiency of ~0.6W/A. We also studied lattice-matched broad-area AlGaAs single QW lasers at ~830 nm for comparison. Typical waveguides were 100 μm wide and cavity lengths were ~1.5 - 2 mm. Accelerated life-tests of our lasers were performed using two different methods − a commercial laser diode lifetester and our TR-EL set-up. We employed various nondestructive FMA techniques to study degradation processes including TR-EL, deep level transient spectroscopy (DLTS), and time resolved photoluminescence (TR-PL) as well as destructive techniques including EBIC and HR-TEM. TR-PL techniques were used to study carrier dynamics in InGaAs-AlGaAs strained QW lasers and InAs-GaAs QD lasers. Carrier lifetimes were measured before and after the lasers were aged. Dark line defect and DLD-free areas were excited by laser pulses from a mode-locked Ti:Sapphire laser with a pulse duration of 120 fsec and a repetition rate of 200 kHz. The excitation wavelength was 900 nm and a Hamamatsu streak camera with an IRF of 30 ps was used for the PL detection. Detailed description of our TR-EL and DLTS techniques was provided in our previous publications [13, 14]. 3. EXPERIMENTAL RESULTS AND DISCUSSION 3.1 Catastrophic Degradation in High Power InGaAs-AlGaAs Strained Quantum Well Lasers We employed our TR-EL techniques to study catastrophic degradation processes in high power broad-area strained InGaAs single QW lasers at 975 nm and high power broad-area lattice-matched AlGaAs single QW lasers at 830 nm as they were stressed under accelerated lifetests. Both types of lasers had windowed n-contacts. We also employed the DLTS technique to study trap characteristics in laser diodes before and after aging and the EBIC technique to identify failure modes by observing DLDs after device degradation. 3.1.1 TR-EL – Real Time Observation of Dark Spots and Dark Lines TR-EL images were captured in real-time from the window region during entire accelerated lifetests under automatic current control (ACC) mode until catastrophic device failure. Our TR-EL set-up with a nominal spatial resolution of 2 μm/pixel allowed us to collect EL images as fast as one image per second during entire lifetests. Among a number of broad-area lasers we studied, results from only two lasers (Samples A and B) are shown in this section. Sample A was an InGaAs strained QW laser and Sample B was an AlGaAs lattice-matched QW laser. Both lasers had a passivation layer on the facets. Test conditions were 6A and Ths=65°C for Sample A and 5A and Ths=25°C for Sample B. Figure 2 (b) – (d) show snapshots of TR-EL images captured from Sample A during accelerated lifetest. Sample A degraded by bulk degradation. Our group has studied a number of InGaAs-AlGaAs broad-area strained QW lasers over the years and found out that the dominant failure mode of these lasers is bulk degradation [10, 13, 14]. The TR-EL images of Sample A clearly show that the laser underwent a series of events starting from a convergence of the filaments at t=t1 as shown in Figure 2 (b). The local gain saturation and spatialhole burning leading to filamentation and self-focusing of light in broad-area lasers [13, 14] can be responsible for optically induced heating, creating a hot spot, which most likely causes the filaments to converge. Figure 2 (a) shows an illustration of optical beam at different distances as it propagates along the longitudinal axis of a broadarea laser. As the illustration shows, the presence of a thermal lens can lead to narrowing and self-focusing of the optical beam as it propagates. When the critical optical power density or threshold for catastrophic optical bulk damage (COBD) is reached via the convergence of the filaments, a significant temperature rise due to strong optical absorption can damage the area, generating a dark spot at t=t2 as shown in Figure 2 (c) and a dark line and dark area at t=t3 as shown in Figure 2 (d). Our group reported that dark line defects typically observed from EL and EBIC images of catastrophically degraded InGaAs broad-area lasers are manifestations of a high density of dislocations [8]. Figure 3 shows snapshots of TR-EL images captured from Sample B. Sample B degraded by facet catastrophic optical mirror damage (COMD). In contrast to Sample A, Sample B showed remarkably different characteristics.


Sample B developed d DLD Ds initiated fro om the front faacet at t=t2 afterr the previous image was capptured at t=t1 w without showing ob bvious converg gence of the fillaments.

At t=t1

Att t=t2

At t=t3

Rear Facett

Locattion A

t'

[ T y p e

[ T y p e

[ T y p e

a

a

a

11

hate (um)

(a)

Front Facet (b)

((c)

(d)

Figure 2. Illustration off optical beam as it propagaates along the longitudinal aaxis (a) and snnap-shots of T TR-EL images cap ptured from Sample A (b - d).


At t=t1

Rear Facet

Front Facet

At t=t2

Figure 3. Snap-shots of TR-EL images captured from Sample B. To understand the microscopic causes of degradation processes, DLTS measurements were performed on Samples A and B before and after aging. Our DLTS measurements on pre-aged InGaAs QW lasers showed EL2 traps (NT= ~2×1013/cm3 or > 2×104 EL2 traps in the strained InGaAs QW layer), but no EL2 traps were found in pre-aged AlGaAs QW lasers. EL2 traps are mainly attributed to arsenic anti-sites that participate as non-radiative recombination centers (NRCs) of injected carriers only in the bulk degradation processes of InGaAs-AlGaAs strained QW lasers. To the best of our knowledge, no other group has ever reported real-time observation of dark spots or dark lines in motion in semiconductor lasers as they are aged. EBIC images were also taken from the catastrophically degraded lasers and these images showed the same dark lines that we observed from the EL images. 3.1.2 Catastrophic Degradation Processes Pre-existing NRCs We proposed a COBD model in our previous publications [13, 14], where nonradiative recombination processes were identified to play a critical role in bulk degradation of state-of-the art GaAs-based lasers. We suggested nonradiative recombination centers (NRCs) as the root causes of the bulk degradation because NRCs are expected to play a similar role for bulk degradation (or COBD) that surface states play for facet degradation (or COMD). Our model is based on our study of trap characteristics in pre- and post-stressed lasers using DLTS. Our DLTS study identified point defects such as arsenic anti-sites forming EL2 traps as potential NRCs and our TR-PL study identified recombination processes in pre- and post-stressed lasers. Optically Induced Hot Spot Formation Spatial hole burning (SHB) is responsible for filamentation as well as thermal lensing (or self focusing) in broad-area lasers [13−15]. The thermal lens (ΔnT) and carrier-induced refractive index change (ΔnC) both affect waveguide properties of a broad-area laser. Assuming the thermo-optic effect coefficient (∂n/∂T) of ~ 2.5×10−4/°C [16], the refractive index step introduced by the thermal lens (ΔnT) is ~ 5×10−3 for a temperature increase (ΔT) of 20°C. The thermally induced index step is always positive and the refractive index gradient of ~ 5×10−3 in transverse direction is of the same order as the effective index step. As we quantitatively showed in our recent publication [17], ΔnC ≈ 6×10−6, indicating that the thermal lensing effect is a dominant contributor in our lasers. Furthermore, the formation of a thermal lens is critical especially for high power multi-mode lasers because it also leads to gain saturation at local areas and a significant increase in optical power density at Location A as indicated in Figure 2. Nonradiative recombination accompanies local heating, which subsequently increases optical absorption. The increase of the absorption coefficient (Δα) due to local heating (ΔT) caused by nonradiative process is given by Equation 1 [9].

Δ α = α 0 ⋅ [exp(

ΔT ΔT ) − 1] ≅ α 0 ⋅ exp( ) 21 . 4 ° C 21 . 4 ° C

(1)

where α0 is the absorption coefficient without local heating.


Three critical events lead ding to COBD include hot spo ot formation, thhermal runawaay, and local m melting. 1. The firsst event occurss when the loccal temperaturre reaches ~1330°C. At this sstage, the locaalized area beggins to strongly ab bsorb lasing ph hotons. When local heating (ΔT) increasess to 130°C, abbsorption coeffficient (Δα) inccreases to 8.7×104 cm-1 assuming g α0 ≈ 200 cm-1. 2. The seccond event occcurs when thee local heating further increaases to ~300°C C. At this staage, Δα increaases to 2.5×108 cm m-1 and a therm mal runaway pro ocess turns on. 3. The theermal runaway y process imm mediately leadss to local mellting and subssequent COBD D when ΔT reeaches ~1200°C (tthe third eventt). Note that the t TR-EL imaages captured from fr Sample A in Figure 2 (bb) – (d) clearlyy showed that S Sample A evenntually developed a dark spot at Location A (Fiigure 2 (c)) folllowed by darkk lines and darkk areas (Figuree 2 (d)). Dark Linee Defects We studied laser diiodes at differeent stages of deegradation. Thhis investigationn was made poossible because ou ur commercial laser diode liife-tester and TR-EL T set-upss are both equuipped with the automatic shhut-off feature thaat automatically y stops the testt when optical output power reaches a presset threshold. M Most of our saamples we studied d degraded by y bulk failure, but we also observed a feew samples thhat degraded bby facet failurre. We investigateed a number off samples afterr they failed caatastrophicallyy and a few saamples before tthey fully deveeloped dark line defects d (DLDs)). Various techn niques were em mployed to stuudy our samplees including TR R-EL, TR-PL, EBIC, and TEM. Figure 4 show ws a snap-shot of TR-EL images captured from Sample C. Sample C ddegraded by C COBD. As shown in Figure 4, Saample C also sh howed well dev veloped dark liine defects as a result of cataastrophic degraadation involving filaments. f

i

Rear Faccet

Front Faacet

Figure 4. Sn nap shot of TR--EL images cap ptured from Saample C duringg accelerated liife-tests.

(a)


ADF (Z and Straiti

Contrast)

wide TEM sample

(b) Figuree 5. EBIC imaage from Sample D (a) and TE EM image from m Sample E (bb). Figure 5 sh hows EBIC im mage from Sam mple D (a) and TEM image frrom Sample E (b). The DLD Ds shown in Figure 5 (a) are duee to the presen nce of high diislocation denssities as show wn in Figure 5 (b). The shappes of DLDs cclearly indicate that filamentatio on plays a criticcal role in degrradation of theese lasers. Sam mples C, D, annd E were all InnGaAs strained QW W lasers. 3.2 Catasttrophic Degradation in High h Power InAs--GaAs Quantu um Dot Laserrs We started d investigation on reliability and a degradation n mechanism iin state-of-the art InAs-GaAss quantum dot lasers. The lasers were grown by b MBE and quantum q dots were w formed bby the Stranskii–Krastanov (S SK) process (oor selfassembly process). p QD Laserrs Device charracteristics of broad-area InA As-GaAs QD lasers were m measured incluuding L-I-V-sppectral measuremeents, thermal reesistance meassurements, and near field andd far field meassurements.

/ 6

5

,." g6

''

b

X=1]3,.==f1CiII=I:G=511=1,IMML,11USG

$S z

4 á3 U_

z

'Or

1

10

12

LD Current (A)

200

250

'ation (h)

(a)

(b)

Figure 6. L-I characteristics measured d from seven InAs-GaAs I QD D lasers at six different tempperatures from m 25 to nd ACC aging test results fro om three InAs-G GaAs QD laserrs (b). 75ºC (a) an


Figure 6 (aa) shows L-I ch haracteristics measured m from seven QD laseers up to 13A uunder CW operration at six diffferent temperaturres ranging frrom 25 to 75 5ºC. Significaant degradationn in slope effficiencies is observed at higher temperaturres possibly du ue to enhanced carrier leakagee at elevated teemperatures. Lifetest Th hree QD laserss (QD Laser 4, QD Laser 5, and a QD Laserr 6) are currenttly under accellerated lifetest (ACC mode). Test conditions are a 13A (QD Laser L 4), 15A (QD Laser 5)), and 17A (QD Laser 6) at the same basee-plate temperaturre of 30ºC. Ourr preset thresho old (or drop in optical outputt power) is 5% % for the lifetestt. Figure 6 (b) shows ACC aging g test results of o the samples. No failure haas occurred. W When failures ooccur, we willl prepare TEM M cross sections off the failures using u focused ion beam and d will perform detailed defecct analysis usinng a high resoolution TEM. TR-PL Wee employed thee angle polishiing technique to t form window ws to three QD D lasers (QD L Laser 1, QD Laaser 2, and QD Laaser 3). TR-PL L measurementts were perform med on these ssamples at RT T. Figure 7 shoows PL decay ccurves measured from f the three QD lasers.

QD Laser 1 QD Laser QD Laser 3

ï

Figure F 7. PL decay d curves measured m from three t InAs-GaA As QD lasers w with windowedd n-metals. Table 1 su ummarizes lifettimes and amp plitudes estimatted using doubble exponentiall. Unlike strainned InGaAs-A AlGaAs single QW W lasers that show a single deecay componen nt with a typiccal lifetime of ~ 7 ns, all threee QD lasers shhowed faster comp ponents follow wed by slower components c an nd significantlyy longer lifetim mes of > 400 nns. These diffeerences need furtheer investigation n. Table 1. Summary S of TR R-PL measurem ment results fro om three InAs--GaAs QD laseers. Sample QD1 QD2 QD3

Faster Com mponent A0 (a. u.) τ0 (ns) 2478 44 2529 37 7272 13

Slower Com mponent A1 (a. u.) τ1 (ns) 1871 428 1498 452 1230 412


4. SUMMARY We investigated catastrophic degradation processes in high power broad-area InGaAs-AlGaAs strained QW lasers using TR-EL, DLTS, TR-PL, EBIC, and TEM techniques. Most of the broad-area lasers that we studied for the present study degraded by a COBD process. Our TR-EL technique could temporally resolve a series of events in broad-area lasers including the formation of hot spot, dark spot, and dark lines via optically induced heating. DLTS was able to identify point defects such as EL2 traps that could behave as highly efficient NRCs to initiate the COBD process that eventually leads to bulk degradation in the broad-area lasers. Carrier lifetimes measured using our TRPL technique showed good correlation between dark line defects in degraded lasers and nonradiative recombination processes. Our various techniques were also employed to study lasers at different stage of degradation including significantly degraded lasers as well as less degraded lasers. We also reported our preliminary results on catastrophic degradation processes in high power broad-area InAs-GaAs QD lasers.

ACKNOWDGMENTS The work described in this paper was performed as part of The Aerospace Corporation's Sustained Experimentation and Research for Program Applications (SERPA). The authors are grateful to Miles Brodie for his help in TEM sample preparation and to Barbara Hill for her help in EBIC sample preparation.

REFERENCES 1. V. Rossin, E. Zucker, M. Peters, M. Everett, and B. Acklin, “High-power high-efficiency 910-980nm broad area laser diodes,” Proc. SPIE 5336, pp.196-202, 2004. 2. B. Schmidt, B. Sverdlov, S. Pawlik, N. Lichtenstein, J. Müller, B. Valk, R. Baettig, B. Mayer, and C. Harder, “9xx high-power broad area laser diodes,” Proc. SPIE 5711, pp. 201-208, 2005. 3. M. Kanskar, T. Earles, T. Goodnough, E. Stiers, D. Botez, and L. J. Mawst, “High power conversion efficiency Al free diode lasers for pumping high power solid state laser systems,” Proc. SPIE 5738, pp. 47-56, 2005. 4. Z. Xu, W. Gao, L. Cheng, A. Nelson, K. Luo, A. Mastrovito, and T. Yang, “High-brightness, high-efficiency 940980nm InGaAs/AlGaAs/GaAs broad waveguide diode lasers,” Technical Digest of Conference on Lasers and Electro-Optics (CLEO), paper CMX4, 2005. 5. V. Gapontsev, I. Berishev, G. Ellis, A. Komissarov, N. Moshegov, O. Raisky, P. Trubenko, V. Ackermann, E. Shcherbakov, J. Steinecke, and A. Ovtchinnikov, “High-efficiency 970 nm multimode pumps,” Proc. SPIE 5711, pp. 42-51, 2005. 6. M. Vanzi, G. Salmini, and R. De Palo, “New FIB/TEM evidence for a REDR mechanism in sudden failures of 980nm SL SQW InGaAs/AlGaAs pump laser diodes,” Microel. Reliab. 40, pp.1753-1757, 2000. 7. K. H. Park, J. K. Lee, D. H. Jang, H. S. Cho, C. S. Park, K. E. Pyun, J. Y. Jeong, S. Nahm, and J. Jeong, “Characterization of catastrophic optical damage in Al-free InGaAs/InGaP 0.98 µm high-power lasers,” Appl. Phys. Lett. 73, pp. 2567-2569, 1998. 8. Y. Sin, N. Presser, B. Foran, and S. C. Moss, "EBIC and HR-TEM study of catastrophic optical damaged high power multi-mode InGaAs-AlGaAs strained quantum well lasers", Technical Digest of Conference on Lasers and Electro-Optics (CLEO), JThA14, pp.1-2, 2008. 9. C. H. Henry, P. M. Petroff, R. A. Logan, and F. R. Merritt, “Catastrophic damage of AlxGa1-xAs doubleheterostructure laser material,” J. Appl. Phys. 50, pp. 3721-3732, 1979. 10. Y. Sin, N. Presser, B. Foran, N. Ives, and S. C. Moss, "Catastrophic facet and bulk degradation in high power multi-mode InGaAs strained quantum well single emitters,” Proc. SPIE 7198 (High-Power Diode Laser Technology and Applications VII), 719818, pp.1-12, 2009. 11. P. Crump, G. Blume, K. Paschke, R. Staske, A. Pietrzak, U. Zeimer, S. Einfeldt, A. Ginolas, F. Bugge, K. Häusler, P. Ressel, H. Wenzel, and G. Erbert, “20W continuous wave reliable operation of 980nm broad-area single emitter diode lasers with an aperture of 96μm,” Proc. SPIE 7198, 719814, 2009. 12. Y. Sin, N.Ives, N. Presser, and S. C. Moss, "Failure mode investigation of high power multi-mode InGaAsAlGaAs strained quantum well lasers using time-resolved EL and EBIC techniques," Technical Digest of Conference on Lasers and Electro-Optics (CLEO), JTuD16, pp.1-2, 2009.


13. Y. Sin, N. Ives, N. Presser, and S. C. Moss, "Root cause investigation of catastrophic degradation in high power multi-mode InGaAs-AlGaAs strained quantum well lasers," Proc. of SPIE 7583 (High-Power Diode Laser Technology and Applications VIII), 758307, pp. 758307-1 - 758307-12, 2010. 14. Y. Sin, N. Ives, S. LaLumondiere, N. Presser, and S. C. Moss, "Catastrophic optical bulk damage (COBD) in high power multi-mode InGaAs-AlGaAs strained quantum well lasers," Proc. of SPIE 7918 (High-Power Diode Laser Technology and Applications IX), 791803, pp. 791803-1 - 791803-12, 2011. 15. J. R. Marciante and G. P. Agrawal, “Controlling filamentation in broad-area semiconductor lasers and amplifiers,” Appl. Phys. Lett. 69, pp. 593-595, 1996. 16. J. P. Kim and A. M. Sarangan, “Temperature-dependent Sellmeier equation for the refractive index of AlxGa1−xAs,” Optics Letters 32, pp. 536 – 538, 2007. 17. Y. Sin, S. LaLumondiere, N. Presser, B. Foran, N. Ives, W. Lotshaw, and S. C. Moss, "Physics of failure investigation in high power broad-area InGaAs-AlGaAs strained quantum well lasers", Proc. SPIE 8241 (HighPower Diode Laser Technology and Applications X), 824116, 2012.
