Comparison of resonant-phonon-assisted terahertz quantum-cascade lasers with one-well injector and three-well module

The authors compare resonant-phonon-assisted terahertz quantum-cascade lasers with different active region designs, i.e., one-well injector and three-well module, using an ensemble Monte Carlo method. Carrier transport under injection anticrossing, parasitic anticrossing, and collection anticrossing couplings are investigated for both structures. The results show that the main parasitic current channel is the resonance of the injector 1(') with the lower lasing level 3 and one-well injector design benefits a high injection selectivity because of a better Delta(')(1)4/Delta(')(1)3 ratio. Due to the diagonal radiative transition, the one-well injector design sacrifices the oscillator strength and modal gain to reduce the parasitic coupling. Temperature evaluation shows that longitudinal-optical phonon emission is the dominant scattering mechanism contributing to lasing and the calculated modal gain in the one-well design shows a slower decreasing rate with temperature.