Abstract
We demonstrate λ ~ 9 μm GaAs/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.45</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.55</sub> 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- μm-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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .
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