  We report on a new design of terahertz quantum cascade laser based on a
single, potential-inserted quantum well active region. The quantum well
properties are engineered through single monolayer InAs inserts. The modeling
is based on atomistic, spds* tight-binding calculations, and performances are
compared to that of the classical three-well design. We obtain a 100% increase
of the oscillator strength per unit length, while maintaining a high, nearly
temperature-independent contrast between phonon-induced relaxation times of the
upper and lower lasing states. The improved performances are expected to allow
THz lasing at room temperature.
