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