We demonstrate λ∼3.5 μm and λ∼3.3 μm strain compensated In0.7Ga0.3As/AlAs(Sb)/InP quantum cascade lasers operating in pulse regime at temperatures up to at least 400 K. Peak optical power exceeding 3.5 W at 300 K has been achieved at both wavelengths for 10 μm wide 4 mm long lasers with high reflectivity coated back facets. Threshold current densities of 2.5 kA/cm2 and 3.5 kA/cm2 have been observed at 300 K for the devices emitting at λ∼3.5 μm and λ∼3.3 μm, respectively.

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We demonstrate m GaAs/Al Ga As quantum cascade lasers (QCLs) operating up to 320 K. Metal-organic vapor phase epitaxy has been used throughout for the growth of the devices. Detailed comparison has been carried out for the QCLs with various waveguides and grown on (100) GaAs substrates with different miscut angles towards (111)A. Introduction of InGaP cladding layers into the optical waveguide significantly improves the QCL performance due to a better optical confinement and lower waveguide losses compared with the GaAs-based waveguide. A 20-m-wide 4-mm-long device with high reflectivity coating on the laser back facet demonstrates room-temperature pulsed output power of 220 mW and a lowered threshold current density of 6.5 kA/cm . Index Terms-Midinfrared quantum cascade lasers (QCLs), optical waveguide.

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Publisher's Note: "High-peak-power strain-compensated GaInAs/AlInAs quantum cascade lasers (λ4.6 μm) based on a slightly diagonal active region design" [Appl.We report on the midinfrared broadband transmission spectroscopy measurements of a ϳ 4.3 m strain compensated In 0.64 Ga 0.36 As/ Al 0.58 In 0.42 As/ InP quantum cascade laser. A detailed experimental analysis of the electronic distribution for bias values below the laser threshold is presented, highlighting the effects of the design with strongly diagonal laser transition. A marked voltage induced Stark shift is observed for the diagonal laser transition while the vertical intersubband transitions involved higher energy levels remained nearly bias independent. We also demonstrate the direct observation of intersubband transitions originating from the ground level of the injector miniband to the level confined above the AlInAs barriers.