Continuous-wave room temperature operated 3.0 μ m type I GaSb-based lasers withquinternary AlInGaAsSb barriersT. Hosoda, G. Belenky, L. Shterengas, G. Kipshidze, and M. V. Kisin Citation: Applied Physics Letters 92, 091106 (2008); doi: 10.1063/1.2890053 View online: http://dx.doi.org/10.1063/1.2890053 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/92/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in 200 mW type I GaSb-based laser diodes operating at 3 μ m : Role of waveguide width Appl. Phys. Lett. 94, 261104 (2009); 10.1063/1.3159819 GaSb-based, 2.2 μ m type-I laser fabricated on GaAs substrate operating continuous wave at room temperature Appl. Phys. Lett. 94, 023506 (2009); 10.1063/1.3072596 Room temperature operated 3.1 μ m type-I GaSb-based diode lasers with 80 mW continuous-wave output power Appl. Phys. Lett. 92, 171111 (2008); 10.1063/1.2919720 Room-temperature operation of 3.26 μ m GaSb-based type-I lasers with quinternary AlGaInAsSb barriers Appl. Phys. Lett. 87, 241104 (2005); 10.1063/1.2140875 High-power room-temperature continuous wave operation of 2.7 and 2.8 μm In(Al)GaAsSb/GaSb diode lasers Appl. Phys. Lett. 83, 1926 (2003); 10.1063/1.1605245

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Continuous-wave room temperature operated 3.0 �m type I GaSb-basedlasers with quinternary AlInGaAsSb barriers

T. Hosoda,1 G. Belenky,1,a� L. Shterengas,1 G. Kipshidze,1 and M. V. Kisin2

1Department of Electrical and Computer Engineering, SUNY, Stony Brook, New York 11794, USA2Power Photonic Corporation, Stony Brook, New York 11790, USA

�Received 2 January 2008; accepted 8 February 2008; published online 4 March 2008�

Diode lasers emitting at 3.0 �m were designed and fabricated. Device active region contained twocompressively strained InGaAsSb quantum wells incorporated in quinternary AlInGaAsSb barriers.Laser output power at room temperature was 130 mW in continuous wave regime and more than1 W in pulse. © 2008 American Institute of Physics. �DOI: 10.1063/1.2890053�

Over the past several years, significant progress wasachieved in development of high power type I GaSb basedquantum well �QW� lasers operating at room temperaturewithin spectral region 2.3–2.8 �m. Devices with InGaAsSbstrained QWs incorporated in AlGaAsSb barriers providehundreds of milliwatt output power in cw regime.1–7 How-ever, the performance of type I GaSb based quantum welllasers at longer wavelength is not so impressive. Only 4 mWoptical power in cw regime at room temperature with wave-length near 3 �m was shown in Ref. 8. Type I lasers basedon AlGaInAsSb / InGaAsSb /GaSb heterostructure showemission at 3.26 �m in pulse mode at temperature up to50 °C.9 Since the spectrum region 3.0–3.5 �m is attractivefor a variety of gas sensing applications, different approacheshad been used to design devices with these characteristics.Emission with wavelength close to 3 �m was registered inpulse mode up to 400 K from intersubband quantum cascadelasers based on InAs /AlSb heterostructure.10 Type II inter-band QC laser based on GaSb substrate demonstrates emis-sion close to 3.3 �m and operates in cw regime up to264 K.11

Earlier, we noted6 that improvement of the hole confine-ment is the decisive factor for development of GaSb basedlaser diodes with enhanced performance. In this paper, weare reporting the characteristics of room temperature operat-ing 3 �m type I GaSb based lasers with improved carrierconfinement. The devices output power at room temperaturein cw regime is 130 mW and in pulse is more than 1 W.

Laser heterostructures were grown using a VeecoGEN-930 solid source molecular beam epitaxy system onTe-doped GaSb substrates. The cladding layers were 2.5and 1.5 �m wide Al0.6Ga0.4As0.07Sb0.93 doped with Te�n-side� and Be �p-side�, respectively. Graded bandgapheavily doped transition layers were introduced between thesubstrate and n-cladding and between the p-cladding andp-cap to assist carrier injection. The nominally undopedAl0.2In0.2Ga0.6As0.2Sb0.8 waveguide layer with a total thick-ness of about 800 nm contained two 12 nm wideIn0.54Ga0.46As0.23Sb0.77 QWs centered in the waveguide andspaced 40 nm apart. Thick waveguide and cladding layerswere lattice matched to GaSb. The compressive strain in theQWs was about 1.8%. The wafer was processed into 100 �mwide oxide confined gain guided lasers. 2 mm long neutral-

reflection ��NR��30% � and high-reflection ��HR��95% �coated lasers were In-soldered episide down onto Au-coatedpolished copper blocks and characterized.

Figure 1 shows the temperature dependence of cw light-current characteristics for 2 mm long NR/HR lasers. Morethan 130 mW cw output power was demonstrated at 290 Kfor the 2 mm long laser with threshold current about 0.6 A.In short pulse low duty cycle mode �200 ns /10 kHz�, the2 mm long devices show no thermal rollover and more than1 W peak power level at 12 A at room temperature �Fig. 2�.At 250 K, the device peak power is more than 1 W at 9 A ofpeak current. The inset in Fig. 2 plots the temperature depen-dences of the 2 mm long device threshold current and effi-ciency. Parameters T0 and T1 characterizing the exponentialincrease of the threshold current and decrease of the externalefficiency with temperature are above 58 and 217 K, respec-tively. Figure 3 presents the modal gain spectra obtained atroom temperature �290 K� by Hakki–Paoli method. From thevalue of the modal gain in the long-wavelength part of thespectra, where the material gain is zero, we can determinethe total optical loss and assuming that mirror loss is about12 cm−1 for 0.92 mm long uncoated �33%� devices, the in-ternal optical loss for 3.0 �m lasers happens to be 14 cm−1.

The results presented above demonstrate that hetero-structures with quinternary AlInGaAsSb waveguide and In-GaAsSb QW layers �this approach was already used to de-

a�Author to whom correspondence should be addressed. Electronic mail:garik@ece.sunysb.edu.

FIG. 1. cw mode output power and spectral characteristics of 2 mm longNR/HR coated device with stripe width 100 �m.

APPLIED PHYSICS LETTERS 92, 091106 �2008�

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sign and fabricate lasers operated at room temperature inpulse mode9� are promising for fabrication of GaSb-basedtype I diode lasers with emission wavelength above 3 �m.Structures with quaternary AlGaAsSb waveguides/barriershave limitations which restrict their use for device develop-ment in this spectral range. The laser operation beyond 3 �mrequires increasing the QW indium concentration above 50%level. In order to keep the mechanical strain low, arsenicconcentration in QW material must be increased. This resultsin strong degradation of the hole confinement in the activeQWs.

Hole confinement in quaternary InGaAsSb /AlGaAsSbheterostructures can be restored by raising the aluminumconcentration in the barrier �waveguide� layers. This leads toreduction of the waveguide refractive index, deteriorating theoptical mode confinement, and to increase of the conductionband discontinuities at QW heterointerfaces. The presence ofdeep QWs for electrons can result in inhomogeneous QWpopulations in multi-QW laser diodes as well as create thesituation of carrier heating during the intrawell electron re-

laxation. Under the condition of weak hole confinement,heating of the hole subsystem can be crucial for the ultimatelaser operation.

Most of the above problems can be resolved by introduc-ing indium into the waveguide composition. Indium notice-ably decreases the direct energy gap of the barrier layers and,therefore, lowers the conduction band discontinuities in theactive QWs. Moreover, the presence of indium in quinter-nary waveguide composition requires increased arsenic con-centration in the waveguide �barrier� layers leading to im-proved hole confinement. Utilizing quinternary waveguides,we can decrease QWs strain and correspondingly increasethe QWs width. Figure 4 illustrates the above considerationsand defines the choice of the material compositions used inthe design of the devices reported in this paper. For calcula-tion of the band edge positions we use the data fromreview.12 Energy gaps were calculated using biquadratic in-terpolation algorithm.13 Valence band positions were ob-tained by linear interpolation. Figure 4 presents the calcu-lated band edge positions at room temperature. It is readilyseen that presence of indium in quintenary alloy stronglydecreases the energy positions of both conduction band andvalence band as compared with quaternary Al0.2GaAsSbcomposition �start points of solid curves marked with shortarrows correspond to quaternary waveguide compositionswithout indium�. Such a decrease favorably balances theconfinement conditions for both electrons and holes. The ver-tical arrows indicate the direct energy gaps for quinternarywaveguide with 20% aluminum and 20% indium �left arrow�and 1.8% strained quaternary QW composition with 54%indium �right arrow�. Figure 4 also shows the band edgepositions for quaternary InGaAsSb alloy lattice matched toGaSb �dash-dotted lines� which would be the best choice inview of aluminum-free waveguide. Note, however, that qua-ternary waveguide with no aluminum added provides insuf-ficient confinement either for holes or for electrons at anycomposition and therefore should be avoided.

In conclusion, we proved that heterostructures withquinternary AlInGaAsSb waveguide and InGaAsSb QW

FIG. 2. Pulse mode �200 ns /10 kHz� output power characteristics. Insetshows the characteristic temperatures T0 and T1.

FIG. 3. Current dependence of the modal gain of 0.92 mm long uncoateddevice at 290 K measured in pulse mode �200 ns /2 MHz�.

FIG. 4. Conduction and valence band positions vs indium concentration forquinternary waveguide lattice matched to GaSb �solid lines� with 20% alu-minum and 1.8% strained InGaAsSb quaternary QW composition �dashedlines�. Thin dash-dotted lines show band positions for quaternary waveguidewith no aluminum. Vertical arrows indicate bulklike energy gaps forwaveguide/QW compositions used in the present devices.

091106-2 Hosoda et al. Appl. Phys. Lett. 92, 091106 �2008�

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layers are promising for fabrication of room temperatureoperating GaSb-based type-I diode lasers with emissionwavelength of 3 �m. Devices based on AlInGaAsSb /InGaAsSb /AlInGaAsSb /GaSb heterostructures demonstrateoptical power 130 mW in cw regime and more than 1 W inpulse at room temperature.

Authors would like to thank Dr. D. Westerfeld of PowerPhotonic Corporation for fruitful discussions. This work wassupported by the NYSTAR Contract No. C020000, AFOSRGrant No. FA9550-04-1-0372, and NSF Grant No.DMR071054.

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