Longitudinal-optical phonon absorption and dephasing in three-level terahertz quantum cascade structures with different injector anticrossings

摘要

The effects of longitudinal-optical phonon scattering and dephasing in quantum cascade structures are studied. Three-level longitudinal-optical phonon depopulated terahertz structures are investigated using a density matrix Monte Carlo method. Ideally, these structures do not contain energy states above the upper lasing state, which in principle, can reduce parasitic leakage. The light output and current density as a function of lattice temperature are calculated and shown to be consistent with experiment for a recently reported structure that is confirmed to be a good approximation to a three-level structure. The pure dephasing time is self-consistently found to be relatively constant over the temperature range, which differs from the previous analysis of other structures. At higher lattice temperatures, particularly at elevated temperatures beyond the lasing point, the reduction in current density is rather due largely to rapid longitudinal-optical phonon absorption, which reduces the lifetime of the ground state. It is shown that the operating temperature limit may further be improved by adequately increasing the injector anticrossing.