High Power Mid-Infrared Interband Cascade Lasers
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B. H. YANG, D. ZHANG, RUI. Q. YANG, C.-H. LIN, S. J. MURRY, H. WU, S. S. PEI Space Vacuum Epitaxy Center, University of Houston, Houston, TX 77204-5507 [email protected] ABSTRACT We have demonstrated 4-p•m InAs/InGaSb/AlSb interband cascade lasers with optical output power close to 0.5 W per facet with l-gs pulses at 1 kHz repetition rate. At 10% duty cycle, an average output power -20 mW was realized. External and internal quantum efficiencies exceeding 200% have been achieved at 80 K. INTRODUCTION High power near-infrared semiconductor lasers have been extensively investigated for applications in data storage, solid-state laser pumping, medical therapy, etc. However, high power semiconductor lasers at mid-infrared atmospheric transmission window are urgently demanded for a number of military and commercial applications such as IR countermeasures, high resolution molecular spectroscopy, industrial process control, free space communications, etc. We have proposed [1-3] and demonstrated [4] a new type of mid-IR quantum cascade (QC) lasers based on interband transitions in type-TI quantum wells. This interband cascade laser takes advantage of the broken-gap band alignment in the InAs/Ga(In)Sb heterostructure to recycle carriers from the valence band back to the conduction band, thus enabling sequential photon emission from active regions stacked in series. Recently, we demonstrated high-power and highefficiency operation of the interband cascade laser. A peak optical output power of- 0.5 W/facet with a slope efficiency of 211 mW/A per facet at -3.9 ptm was obtained with I pLs current pulses at 80 K [5]. The threshold current density at 80K was 290 A/cm 2 which is substantially lower than those reported for the QC lasers. The characteristic temperature was 80 K at temperatures up to 165 K. The slope efficiency was 211 mW/A per facet, corresponding to a differential external quantum efficiency of 130%, or 1.3 emitted photons per injected electron. Comparable external quantum efficiency, with a peak output power of 430 mW/facet and a slope efficiency of 274 mW/A per facet were also reported with a "W" configuration 2.9 pgm cascade laser when pumped with 100 ns current pulses at 100 K [6]. At 180 K, the maximum output power was 252 mW/facet with a slope efficiency of 188 mW/A per facet. We report here 4-ptm interband cascade lasers with quantum efficiencies > 200% and average optical output powers 20 mW for the first time. EXPERIMENT The laser structure was grown with a Riber 32 MBE system on a rotating p-type GaSb substrate. The substrate temperature was kept at about 440°C during growth and the wafer was annealed at higher temperatures to improve the material quality. High-resolution double crystal X-ray diffraction was used to characterize the crystalline quality. The active region of the laser structure comprises 23 periods of coupled InAs/GalnSb/AISb QWs which are connected by digitally graded n-type lnAs/AllnSb injection layers as reported previously [5]. 89 Mat. Res. Soc. Symp. Proc. Vol. 484 ©1998 Materials
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