Quantum cascade laser operation with high duty cycle

Summary form only given. The emitted wavelength of quantum cascade (QC) lasers is essentially determined by quantum confinement as these devices are based on intersubband transitions. The wavelength is usually designed by thickness modelling of the different lattice matched layers within the active region. By changing the indium composition one can further increase the energy difference between the intersubband states and thus reach wavelengths below 5 /spl mu/m at the cost of introducing strain into the structure. In such structures the overall stress of a period should be zero and each strained layer must not exceed the critical layer thickness to remain in a two-dimensional growth mode without strain relaxation and dislocation generation. We present lattice matched and strain compensated QC lasers with,a four quantum well active region designed for emission at /spl sim/10 /spl mu/m and 5 /spl mu/m, respectively. The four quantum well design makes use of short lifetime of the lower lasing state and a good injection efficiency. The lower waveguide cladding and the waveguide core with the active region consist of ternary InAlAs and InGaAs compounds.