Engineering of electron–longitudinal optical phonon coupling strength in m-plane GaN terahertz quantum cascade lasers

In this work nonpolar (m-plane) GaN terahertz quantum cascade lasers are designed based on the non-equilibrium Green's function method. The lasing quantum-level broadening that arises from electron–longitudinal optical (LO) phonon coupling is studied by tuning the coupling strength, and the changes of optical gain due to this broadening are demonstrated in a self-consistent way. It is found this coupling process largely widens the linewidth of intersubband transition and then quenches the lasing even at a low temperature of 10 K. The electron–LO phonon coupling strength, however, can be manually engineered by tailoring the quantum well structure. As a result, the optical gain will be recovered above the cavity threshold, indicating a potential for terahertz lasing from GaN semiconductors.