Doping dependence of electron populations in optically pumped step quantum well structures

Transient electron dynamics in quantum well (QW) structure is very important for designing terahertz (THz) lasers based on subband transitions. In this paper, four three-level (indexed by 0, 1 and 2) asymmetric stepped GaAs/AlxGa1−xAs QW structures with different doping conditions are designed, and an ensemble Monte Carlo method is adopted to comparatively analyze the corresponding electron dynamics. We find that transient population reversion between upper two subbands is strongly dependent on a low doping density and doping position far away from electron ensemble to reduce electron–electron (EE) scattering and impurity scattering. The results also show that three types of EE scattering, E21E00, E22E01 and E21E22, subscripts representing the initial and final levels of an electron, dominate the EE scattering contribution to the transient population reversion. The ground state is found to have the highest average energy among the three levels, which may seriously weaken the optical pumping efficiency