Terahertz intersubband electroluminescence from n-type germanium quantum wells

The Quantum Cascade Laser (QCL) has been demonstrated in polar III-V semiconductor materials employing transitions between conduction band states [1] . Harnessing intersubband transitions allows lasing at mid-infrared and far-infrared wavelengths. Buried InGaAs/InAlAs QCLs unlocked the mid-infrared application space, because they are operational at room-temperature and in continuous wave [2] . However, THz QCLs remain limited up to 250 K in pulsed operation with a large dissipation [3] . The quenching of the laser emission is related to ther-mally activated LO phonon emission in polar materials. Exploiting intersubband transitions in non-polar group IV materials with weaker electron-phonon interaction is an exciting approach to realize a Si-based THz QCL and to eventually elevate the operation temperature [4] .