Self-consistent solutions to the intersubband rate equations in quantum cascade lasers:: Analysis of a GaAs/AlxGa1-xAs device

The carrier transition rates and subband populations for a GaAs/AlGaAs quantum cascade laser operating in the mid-infrared frequency range are calculated by solving the rate equations describing the electron densities in each subband self-consistently. These calculations are repeated for a range of temperatures from 20 to 300 K. The lifetime of the upper laser level found by this self-consistent method is then used to calculate the gain for this range of temperatures. At a temperature of 77 K, the gain of the laser is found to be 34 cm(-1)/(kA/cm(-2)), when only electron-longitudinal-optical phonon transitions are considered in the calculation. The calculated gain decreases to 19.6 cm(-1)/(kA/cm(-2)) when electron-electron transition rates are included, thus showing their importance in physical models of these devices. Further analysis shows that thermionic emission could be occurring in real devices. (C) 2001 American Institute of Physics.