Native-Oxide-Confined Mid-IR Quantum Cascade Lasers Via Non-Selective Oxygen-Enhanced Wet Oxidation

In this work, a novel self-aligned process utilizing non-selective, O-2-enhanced wet thermal oxidation is presented for fabricating InP-based, ridge waveguide mid-infrared (lambda=5.4 mu m) quantum cascade lasers (QCLs) with a strain-compensated, 30-stage (1.53 mu m thick) InGaAs/AlInAs active region, grown via metal organic chemical vapor deposition. This process, previously used in GaAs-based diode lasers containing low-Al content AlGaAs or even Al-free III-As alloys, forms a highly-insulating native oxide layer while simultaneously smoothing and passivating the etch-exposed active region, resulting in low-loss, strongly-confining waveguides. Here we report the first application of this process for directly oxidizing the deeply-etched QCL InGaAs/AlInAs active region ridge waveguide sidewalls and field (outside the ridge), eliminating the need for a deposited dielectric for electrical isolation, thus allowing self-aligned device fabrication. An 8 hour, 500 degrees C wet oxidation with 7000 ppm added O-2 (relative to N-2 carrier gas) yields a uniform oxide of similar to 350 nm in the field outside the ridge to similar to 500 nm on the ridge sidewall. Laser devices tested under room temperature, pulsed excitation exhibit a threshold current density of J(th)similar to 3.2 kA/cm(2) for a 19.5 m wide x 3 mm long stripe width.