Quantum cascade lasers (QCLs) are novel semiconductor devices. Unlike ordinary band gap lasers known from everyday life (laser pointers, Blu-ray/DVD/CD drives), they are using a radically new concept. The energy levels in a quantum cascade laser are formed by quantum mechanically bound states in an artificially grown semiconductor nanostructure. Therefore they are also known as intersubband lasers.


To push the current limits of terahertz quantum cascade lasers we employ novel semiconductor material systems and compensate for imperfections on the atomic level. We have demonstrated performance records with novel InP-based material combinations (InGaAs/GaAsSb) and developed symmetric active regions which are a perfect tool to study growth-related problems such as interface roughness asymmetry and dopant migration.
(C. Deutsch)


Quantum cascade lasers are very promising sources of coherent terahertz radiation for future applications. We considerable improved the device performance by increasing the active region thickness of the laser using a stacking process. The improved optical properties combined with the increased light generation results in a high power THz laser with a record high pulsed output power of almost 1 W.
(M. Brandstetter)


Carrier relaxation has a significant influence on the efficiency of quantum-well-based optoelectronic devices. In terahertz quantum cascade lasers, for example, non-radiative scattering processes are quickly depopulating the upper laser level, reducing the optical gain and limiting the maximum operating temperature. Low-dimensional nanostructures, like semiconductor nanowires, introduce an additional quantum mechanical confinement in the plane of a quantum well structure. We study the prospects and technological challenges of realizing such an additional quantization to enhance the lifetimes of excited states.
(M. Krall)