Short-wavelength (λ≈3.3 μm) InP-based strain-compensated quantum-cascade laser

The authors describe the design and implementation of a short-wavelength quantum-cascade laser emitting at approximately 3.3 mu m at 80 K. The active region is based on the strain-compensated In0.73Ga0.27As-In0.55Al0.45As-AlAs heterosystem on InP. The band structure and the strain are controlled through the use of both composite barriers as well as composite wells. The structure is designed so the transition resulting in laser emission is very spatially diagonal; the upper laser state is primarily located in a thick In0.55Al0.45As layer in the injector while the lower laser state is in an In0.73Ga0.27As well. This design allows the lasing transition to bypass (in energy-growth-coordinate space) the lowest indirect X and L valleys of In0.73Ga0.27As, and population inversion is achieved in spite of the upper laser state reaching the energy of the indirect X- and L-valley edges of the adjacent In0.73Ga0.27As well. (c) 2006 American Institute of Physics.