Nonresonant tunneling phonon depopulated GaN based terahertz quantum cascade structures

GaN based terahertz quantum cascade structures are theoretically studied. Since the Frohlich interaction is similar to 15 times higher in GaN than in GaAs, level broadening makes obtaining appreciable optical gain difficult even with a large population inversion. A density matrix Monte Carlo method is used to calculate the broadening of the optical gain spectra as a function of lattice temperature. We find by using a proposed method of nonresonant tunneling and electron-longitudinal-optical phonon scattering for depopulation of the lower lasing state, that it is possible to sufficiently isolate the upper lasing state and control the lower lasing state lifetime to obtain high optical gain in GaN. The results predict lasing out to 300 K which is significantly higher than for GaAs based structures. [http://dx.doi.org/10.1063/1.4801947]