Intersubband electron-electron scattering in asymmetric quantum wells designed for far-infrared emission

Population inversion in inter-subband emitters and lasers depends critically on the lifetimes of the nonradiative inter-subband transitions. We find that the often neglected Auger-type processes and Pauli exclusion effects can dominate the electron-electron scattering contributions to the total scattering rate. Electron exchange is also considered. In a range of three-level asymmetric quantum-well structures designed to produce terahertz radiation, we estimate the potential for laser operation for a range of electron densities and temperatures using the population ratio ${\tau }_{32}/{\tau }_{21}.$ We find that predicted population ratios have a strong dependence on the electron-electron scattering rates, and that Auger processes and Pauli exclusion are of particular importance. In addition, the temperature dependence of the population ratio is significantly altered by the inclusion of electron-electron scattering processes. Our results indicate that the interplay of electron-phonon and electron-electron scattering rates suggest optimum operating temperatures for different emitter frequencies.