Terahertz bound-to-continuum quantum-cascade lasers based on optical-phonon scattering extraction

In this paper we present a new QC THz laser with a design that combines the advantages of the bound-to-continuum approach together with the use of an LO phonon resonance to enable fast scattering of the carriers out of the lower miniband. As compared to the previous bound-to-continuum design the large energy separation significantly reduces the lower state lifetime by allowing optical phonon scattering from electrons with very small in-plane kinetic energy and reduces the thermal backfilling of the lower state. Processing of the devices has been performed using both single plasmon and double metal waveguides. Laser emission takes place at an energy of 14.9 meV just after threshold, in good agreement with the designed photon energy. Pulsed operation could be observed up to an heatsink temperature of 116 K in a 1.5 mm-long. 110 μm wide laser ridge with HR backfacet coating. CW operation is possible in narrow stripes because of the high lateral mode confinement provided by the double-metal waveguide and maximum operating temperature rises up to 53 K in a 0.75 mm-long, 70 μm wide laser ridge.