Ultralow threshold current terahertz quantum cascade lasers based on double-metal buried strip waveguides

Terahertz (THz) quantum cascade lasers based on a buried cavity geometry are demonstrated by combining double-metal waveguides with proton implantation. Devices are realized with emission at 2.8 THz, displaying ultralow threshold currents of 19 mA (127A∕cm2) at 4 K in both pulsed and continuous wave operation. Owing to the semiconductor material on both sides of the active region and to the narrow width of the top metal strip, the thermal properties of these devices have been greatly improved. A decrease of the thermal resistance by over a factor of two compared to standard ridge double-metal lasers of similar size has been measured.