Continuous-wave operation of terahertz quantum-cascade lasers above liquid-nitrogen temperature

We report cw operation of a quantum-cascade laser at 3.2 THz (lambdaapproximate to94 mum) up to a heat-sink temperature of 93 K. Resonant longitudinal-optical phonon scattering is used to depopulate the lower radiative state and a low-loss metal-metal waveguide is used to provide high modal confinement. Optical powers of similar to1.8 mW at 10 K and similar to400 muW at 78 K are observed from a single facet of a 40-mum-wide and 1.35-mm-long laser device. A threshold current density of 432 A/cm(2) at 10 K and 552 A/cm(2) at 78 K was obtained in cw mode. The same device lased up to 129 K in pulsed mode with a threshold current density of 419 A/cm(2) at 5 K. (C) 2004 American Institute of Physics.