Temperature dependences of the threshold current and output power of a quantum-cascade laser emitting at 3.3 THz

The active region of a THz (terahertz) quantum-cascade laser based on three tunnel-coupled GaAs/Al$_{0.15}$Ga$_{0.85}$As quantum wells with a resonance-phonon depopulation scheme is designed. Energy levels, matrix elements of dipole transitions, and gain spectra are calculated as functions of the applied electric-field strength $F$ and temperature. It is shown that the maximum gain is implemented at a frequency of 3.37 THz and $F$ = 12.3 kV/cm. Based on the proposed design, a quantum-cascade laser emitting at $\sim$3.3 THz with a double metal waveguide and $T_{\operatorname{max}}$ $\sim$ 84 K is fabricated. The activation energy $E_a$ = 23 meV for longitudinal-optical (LO) phonon emission upon the stimulated recombination of hot electrons from the upper laser level to the lower one is determined from the Arrhenius temperature dependence of the output power.