Design of n-type silicon-based quantum cascade lasers for terahertz light emission

The design of terahertz quantum cascade lasers based on electronic intersubband transitions in Ge∕SiGe quantum wells is investigated. A detailed theoretical model of the conduction-band lineup of these heterostructures is first presented and used to show that large quantum confinement in the L valleys can be obtained with properly selected layer compositions and thicknesses. Computation of the key laser design parameters is then discussed, including the important role played by the L-valley ellipsoidal constant-energy surfaces. Finally, the main design issues specific to this material system and its potential for high-performance operation are illustrated by means of two exemplary structures, designed for emission near 50 and 25μm.