Optimized energy separation for phonon scattering in three-level terahertz intersubband lasers

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Abstract
We examine the impact of the complex phonon spectrum on the design rules for three-level THz intersubband emitters that utilize resonant optical phonon scattering to obtain intersubband population inversion. In GaAs/AlxGa1−xAs multiple quantum wells, electron–optical phonon scattering occurs due to interaction with “GaAs-like” modes at ℏωLO∼36 meV and “AlAs-like” modes at ℏωLO∼47 meV. Scattering rates are calculated for interface and confined phonon modes to determine the optimal subband energy separations for enhancement of fast depopulation scattering and reduction of parasitic nonradiative scattering. While the results depend sensitively on details of the structure, we find that, for electrically pumped THz lasers, there is not an overwhelming advantage in increasing the subband separation to allow scattering by the higher energy modes. © 2001 American Institute of Physics.