Lasing is reported for ridge-waveguide devices processed from a 40-stage InP-based quantum cascade laser structure grown on a 6-inch Ge-coated silicon substrate with a metamorphic buffer. The structure used in the proof-of-concept experiment had a typical design, including an Al0.78In0.22As/In0.73Ga0.27As strain-balanced composition, with high strain both in quantum wells and barriers relative to InP, and an all-InP waveguide with a total thickness of 8 µm. Devices of size 3 mm x 40 µm, with a high-reflection back facet coating, emitted at 4.35 µm and had a threshold current of approximately 2.2 A at 78 K. Lasing was observed up to 170 K. A preliminary surface morphology analysis suggests that laser performance for QCLs-on-Si devices can be significantly improved by reducing strain for the active region layers relative to InP bulk waveguide layers surrounding the laser core. Additional experimental data on material quality, including threading dislocation density, will be presented in the talk and compared for the same design grown on three different substrates to demonstrate how material quality impacts laser performance. The three substrates to be studied are the following: a native InP substrate, a GaAs substrate (~ 4 % lattice mismatch with InP), and a Si substrate (~ 8 % lattice-mismatch with InP).
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