M-plane GaN terahertz quantum cascade laser structure design and doping effect for resonant-phonon and phonon-scattering-injection schemes

Non-equilibrium Green’s function method has been employed to solve carrier distribution, current density and gain properties for non-polar m-plane GaN terahertz quantum cascade laser (THz-QCL) structures. One is traditional three-wells resonant-phonon (RP) design scheme. The other is two-wells phonon scattering injection (PSI) design scheme. The peak gain of 41.8 and 44.2 cm-1 have been obtained at 8.2 and 7.7 THz respectively at 300 K according to the self-consistent calculation. Different from the usual GaAs two-wells design, the upper and lower lasing levels are both ground states in the GaN quantum wells for the PSI scheme, mitigating the severe broadening effect for the excited states in GaN. To guide the fabrication of such devices, the doping effect on the peak gain has been analyzed. The two designs have demonstrated distinct doping density dependence and it is mainly attributed to the very different doping dependent broadening behaviors. The results reveal the possibility of GaN based THz-QCL lasing at room temperature.