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

Abstract

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/Al x Ga 1−x As 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, E 21 E 00 , E 22 E 01 and E 21 E 22 , 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.

Numerical design of AlGaN/GaN double quantum wells for intersubband absorption in the wavelength range ofλ9.3–10.6 μm

“…In the case of small intersubband energy separation, EE scattering may become more prominent, compared with that of larger subband separation. So in addition to we have carefully treated EE and ionized impurity scatterings in this study, in the same ways as those in our previous studies [5,21,22].…”