Quantum Cascade Lasers (QCLs), operating in continuous wave (cw) at room temperature
(rt) in 3-3.5μm spectral range, which overlaps the spectral fingerprint region of many hydrocarbons,
is essential in spectroscopic trace gas detection, environment monitoring, and pollution control. A
3μm QCL, operating in cw at rt is demonstrated. This initial result makes it possible, for the most
popular material system (AlInAs/GaInAs on InP) used in QCLs in mid-infrared and long-infrared, to
cover the entire spectral range of mid-infrared atmospheric window (3-5μm).
In0.79Ga0.21As/In0.11Al0.89As strain balanced superlattice, which has a large conduction band
offset, was grown. The strain was balanced with composite barriers (In0.11Al0.89As /In0.4Al0.6As) in
the injector region, to eliminate the need of extremely high compressively strained GaInAs, whose
pseudomorphic growth is very difficult.