Magnetic Field Assisted sub-THz Quantum Cascade Lasers

In THz QCLs radiative transitions take place between closely-spaced 2D electronic subbands (1THz~$\sim $~4meV) of a multi-QW semiconductor system. THz quantum cascade lasers now cover the frequency range from 1.2 THz to 5 THz, though cryogenic cooling is still required. Further progress towards the realization of devices emitting at longer wavelengths (sub-THz QCLs) and higher temperatures may be realized in a system with additional lateral confinement. Here we use strong magnetic fields to achieve quasi-0D confinement in THz QCL based on the resonance phonon design. We studied two designs: (a) 2-well injector/2 well active region, emitting at 3~THz at B=0; and (b) 1-well injector/3-well active region, emitting at 2~THz at B=0~T. By applying the appropriate electrical bias and strong magnetic fields, we achieved laser emission at 0.8-0.9~THz at B$>$16~T [1], and 0.6~THz at B$\sim $17~T, from devices a and b respectively. The ability to achieve sub-THz lasing is due to magnetic field enhanced population inversion in a quasi-0D QCL. [1] Wade, A et. al., \textit{Magnetic field assisted Terahertz quantum cascade laser operating up to 225K, }\textbf{Accepted for publication Nature Photonics} (2009)