Predictive quantum theory of current and optical gain in quantum cascade lasers

We have developed a flexible and accurate self consistent non-equilibrium Green’s functions method for stationary charge transport and optical gain in terahertz quantum cascade lasers. We compare our theoretical results with experimental data of a THz-QCL and find excellent quantitative agreement for the current- voltage characteristics and the peak gain energy. We identify non-radiative losses of electrons of the upper laser level to efficiently increase the threshold current and propose an optimized design that suppresses this coherent leakage.