Optimized energy separation for phonon scattering in three-level terahertzintersubband lasers

We examine the impact of the complex phonon spectrum on the design rules fo r three-level THz intersubband emitters that utilize resonant optical phono n scattering to obtain intersubband population inversion. In GaAs/AlxGa1-xA s multiple quantum wells, electron-optical phonon scattering occurs due to interaction with "GaAs-like" modes at (h) over bar omega (LO)similar to 36 meV and "AlAs-like" modes at (h) over bar omega (LO)similar to 47 meV. Scat tering rates are calculated for interface and confined phonon modes to dete rmine the optimal subband energy separations for enhancement of fast depopu lation 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 ener gy modes. (C) 2001 American Institute of Physics.