Subband electronic temperatures and electron-lattice energy relaxation in terahertz quantum cascade lasers with different conduction band offsets

The electronic temperatures of the conduction subbands, the local lattice temperature, and the electron-lattice energy relaxation times (tau(E)) in bound-to-continuum GaAs/AlxGa1-xAs quantum cascade lasers, operating at 2.9 and 2 THz, are reported. This information has been gathered from the analysis of microprobe photoluminescence spectra collected during device continuous wave operation. We find that the electronic distributions in both the active region and the injector are thermalized and that all subbands share the same electronic temperature. The efficiency of electron cooling increases with the conduction band offset.