  We investigate room temperature lasing of terahertz quantum cascade lasers
using quantum dot chains as active material suitable for wireless communication
and imaging technologies. Bandstructure calculations for such extended systems
of coupled quantum dots are made possible by a novel 'linear combination of
quantum dot orbitals'--method, based on single quantum dot wavefunctions. Our
results demonstrate strong vertical-emission of coupled quantum dots, reduced
phonon coupling and in-plane scattering, enabling room-temperature lasing with
significantly reduced threshold current densities.
