Strong confinement in terahertz intersubband lasers by intense magnetic fields

Abstract

Terahertz intersubband lasers based on different optical transitions are investigated under an intense magnetic field applied perpendicularly to the plane of the epilayers, reaching the limit where the cyclotron energy exceeds many times the photon energy. Lasing thresholds as low as $0.65\phantom{\rule{0.3em}{0ex}}\mathrm{A}∕{\mathrm{cm}}^{2}$, together with a strong increase of the laser efficiency demonstrate the long intersubband relaxation times achieved in the intrawell samples by the induced three dimensional confinement. The radically different behavior observed for the bound-to-continuum structures highlights the role of interface roughness scattering at low energy subband spacing.