Electron-electron scattering in far-infrared quantum cascade lasers

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Abstract
A large depolarization shift indicates a strong nonequilibrium intersubband electron-electron scattering (Γ) in tunneling structure. For a far-infrared subband separation Δ∼10 meV, the rate Γ scales with the upper-subband occupation and is never significantly reduced by screening. Despite this nonradiative decay a finite population inversion can be maintained. Finally, the applied bias changes the wave-function symmetry so as to cause a dramatic variation of the electron-electron scattering rate. © 1996 The American Physical Society.