Thermally Activated Longitudinal Optical Phonon Scattering of a 3.8 THz GaAs Quantum Cascade Laser

Thermally activated longitudinal optical (LO) phonon scattering time (τ thermal LO ) of excited subbands in a 3.8 THz quantum cascade laser is studied. The active region used herein is based on a LO phonon depopulation scheme. A single plasmon waveguide was used for optical confinement. By calculating the temperature dependence of threshold current density ( J th ) and comparing with the experiment, τ thermal LO limiting the characteristic temperature of J th is estimated: τ thermal LO is 246 ns at 5 K, which rapidly decreases 15 ps when temperature rises up to 100 K.