  Quantum cascade lasers made of nanowire axial heterostructures are proposed.
The dissipative quantum dynamics of their carriers is theoretically
investigated using non-equilibrium Green functions. Their transport and gain
properties are calculated for varying nanowire thickness, from the
classical-wire regime to the quantum-wire regime. Our calculation shows that
the lateral quantum confinement provided by the nanowires allows an increase of
the maximum operation temperature and a strong reduction of the current density
threshold compared to conventional terahertz quantum cascade lasers.
