Terahertz quantum cascade lasers with double-resonant-phonon depopulation

We present two different terahertz quantum cascade laser (QCL) designs based on GaAs/Al0.3Ga0.7As heterostructures that feature a depopulation mechanism of two longitudinal-optical phonon scattering events. This scheme is intended to improve high temperature operation by reducing thermal backfilling of the lower radiative state. The better of these two devices displays a threshold current density of 170 A/cm(2) at 5 K and lases up to 138 K in pulsed mode and 105 K in continuous-wave mode. However, contrary to expectation, we observed no improvement in temperature performance compared to single-resonant-phonon designs, which suggests that the thermal backfilling is not yet a limiting factor for high temperature terahertz QCL operation.