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1. Long wavelength interband cascade lasers

   https://doi.org/10.1063/5.0084565  

   Massengale, J. A.; Shen, Yixuan; Yang, Rui Q.; Hawkins, S. D.; Klem, J. F. (February 2022, Applied Physics Letters)

   InAs-based interband cascade lasers (ICLs) can be more easily adapted toward long wavelength operation than their GaSb counterparts. Devices made from two recent ICL wafers with an advanced waveguide structure are reported, which demonstrate improved device performance in terms of reduced threshold current densities for ICLs near 11  μm or extended operating wavelength beyond 13  μm. The ICLs near 11  μm yielded a significantly reduced continuous wave (cw) lasing threshold of 23 A/cm²at 80 K with substantially increased cw output power, compared with previously reported ICLs at similar wavelengths. ICLs made from the second wafer incorporated an innovative quantum well active region, comprised of InAsP layers, and lased in the pulsed-mode up to 120 K at 13.2  μm, which is the longest wavelength achieved for III–V interband lasers. 

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2. Low Threshold, Long Wavelength Interband Cascade Lasers With High Voltage Efficiencies

   https://doi.org/10.1109/JQE.2023.3314098  

   Massengale, Jeremy A; Shen, Yixuan; Yang, Rui Q; Hawkins, Samuel D; Muhowski, Aaron J (December 2023, IEEE Journal of Quantum Electronics)

   We report on the substantial advancement of long wavelength InAs-based interband cascade lasers (ICLs) utilizing advanced waveguides formed from hybrid cladding layers and targeting the 10-12 μm wavelength region. Modifications in the hole injector have improved carrier transport in these ICLs, resulting in significantly reduced threshold voltages (Vth) as low as 3.62 V at 80 K. Consequently, much higher voltage efficiencies were observed, peaking at about 73% at 10.3 μm and allowing for large output powers of more than 100 mW/facet. Also, low threshold current densities (Jth) of 8.8 A/cm2 in cw mode and 7.6 A/cm2 in pulsed mode near 10 μm were observed; a result of adjustments in the GaInSb hole well composition intended to reduce the overall strain accumulation in the ICL. Furthermore, an ICL from the second wafer operating at a longer wavelength achieved a peak voltage efficiency of 57% at 11.7 μm, with a peak output power of more than 27 mW/facet. This ICL went on to lase beyond 12 μm in both cw and pulsed modes, representing a new milestone in long wavelength coverage for ICLs with the standard W-QW active region. 

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3. ∼8.5 μ m-emitting InP-based quantum cascade lasers grown on GaAs by metal-organic chemical vapor deposition

   https://doi.org/10.1063/5.0122272  

   Xu, S.; Zhang, S.; Kirch, J. D.; Suri, S.; Pokharel, N.; Gao, H.; Kim, H.; Dhingra, P.; Lee, M. L.; Botez, D.; et al (October 2022, Applied Physics Letters)

   Room-temperature, pulsed-operation lasing of 8.5  μm-emitting InP-based quantum cascade lasers (QCLs), with low threshold-current density and watt-level output power, is demonstrated from structures grown on (001) GaAs substrates by metal-organic chemical vapor deposition. Prior to growing the laser structure, which contains a 35-stage In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As lattice-matched active-core region, a ∼2  μm-thick nearly fully relaxed InP buffer with strained 1.6 nm-thick InAs quantum-dot-like dislocation-filter layers was grown. A smooth terminal buffer-layer surface, with roughness as low as 0.4 nm on a 10 × 10  μm 2 scale, was obtained, while the estimated threading-dislocation density was in the mid-range × 10 8  cm −2 . A series of measurements, on lasers grown on InP metamorphic buffer layers (MBLs) and on native InP substrates, were performed for understanding the impact of the buffer-layer's surface roughness, residual strain, and threading-dislocation density on unipolar devices such as QCLs. As-cleaved devices, grown on InP MBLs, were fabricated as 25  μm × 3 mm deep-etched ridge guides with lateral current injection. The results are pulsed maximum output power of 1.95 W/facet and a low threshold-current density of 1.86 kA/cm 2 at 293 K. These values are comparable to those obtained from devices grown on InP: 2.09 W/facet and 2.42 kA/cm 2 . This demonstrates the relative insensitivity of the device-performance metrics on high residual threading-dislocation density, and high-performance InP-based QCLs emitting near 8  μm can be achieved on lattice-mismatched substrates. 

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4. Enhanced performance of InAs-based interband cascade lasers emitting between 10–13 µm

   https://doi.org/10.1088/1361-6641/acac4e  

   Massengale, Jeremy A; Shen, Yixuan; Yang, Rui Q; Hawkins, Samuel D; Klem, John F (December 2022, Semiconductor Science and Technology)

   Abstract Interband cascade lasers (ICLs) based on the type-II quantum well (QW) active region have attracted much attention for a range of practical applications in the mid-infrared due, in part, to their low power consumption. However, extending the operating wavelength of these ICLs into the long-wave infrared region presents several challenges including the reduced thermal conductivity of the optical cladding layers and the diminished wavefunction overlap in the type-II QW. One solution to alleviate the former concern is to use InAs-based ICLs. To solve the latter problem, InAs 0.5 P 0.5 barriers are introduced in the active region, which lowers the electronic energy level and allows for the InAs well width to be reduced at longer emission wavelengths. Here the advancement of long wavelength ICLs, made from four new InAs-based ICL wafers grown by molecular beam epitaxy, is reported. These ICLs lased in the wavelength range from 10 to 13 µ m and showed significantly improved performance compared with previous ICLs, including the first demonstration of broad-area devices operating in continuous wave mode beyond 12 µ m. These ICLs exhibited substantially increased output powers with reduced threshold voltages ( V th ) and current densities ( J th ). They operated at temperatures up to 40 K higher than previous ICLs at similar wavelengths. 

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5. Pushing the performance limits of long wavelength interband cascade lasers using innovative quantum well active regions

   https://doi.org/10.1063/5.0162500  

   Shen, Yixuan; Massengale, J A; Yang, Rui Q; Hawkins, S D; Muhowski, A J (July 2023, Applied Physics Letters)

   We report significantly enhanced device performance in long wavelength interband cascade lasers (ICLs) by employing a recently proposed innovative quantum well (QW) active region containing strained InAsP layers. These ICLs were able to operate at wavelengths near 14.4 μm, the longest ever demonstrated for III–V interband lasers, implying great potential of ICLs to cover an even wider wavelength range. Also, by applying the aforesaid QW active region configuration on ICLs at relatively short wavelengths, ICLs were demonstrated at a low threshold current density (e.g., 13 A/cm2 at 80 K) and at temperatures up to 212 K near 12.4 μm, more than 50 K higher than the previously reported ICLs with the standard W-shape QW active region at similar wavelengths. This suggests that the QW active region with InAsP layers can be used to improve device performance at the shorter wavelengths. 

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