GaN-based intersubband structures and mid-infrared quantum cascade lasers with heterogeneous cascades

We review two recent developments in the field of quantum cascade lasers. First, early studies of the GaN/AlGaN material system demonstrate the suitability of the latter for the communications wave-length range. Intersubband absorption measurements at wavelengths as short as λ≥ 1.35 μm are reported in multiple coupled quantum wells. An electron scattering time of few 100 fs between the subbands is obtained. Secondly, in InP-based quantum cascade lasers, the recent development of lasers with heterogeneous cascades, i.e. lasers with stacks of many intentionally dissimilar active regions interleaved with injectors is leading to novel concepts for multi-wavelength operation. We report broadband optical gain from 5 to 8 μm and Fabry-Perot laser action covering all wavelengths from 6 to 8 μm simultaneously in a single device.