The nature of the electron distribution functions in quantum cascade lasers

There has been much speculation about the nature of the electron distribution functions in quantum cascade lasers, in particular: Are they non equilibrium and if so, to what extent? In order to address this, detailed calculations of the intersubband and intrasubband electron-longitudinal phonon and electron–electron scattering rates in a real GaAs/AlxGa1−xAs device design [Sirtori et al., Appl. Phys. Lett. 73, 3486 (1998)] are presented. The results suggest that two important conclusions relating to the electron distribution functions in the quantum well subbands can be drawn: the electron distributions in both the active region and the injector subbands are thermalized, i.e., they can be described by Fermi–Dirac distribution functions and furthermore all the electron distributions have the same electron temperature.