Comparison of the quantum efficiencies of interwell and intrawell radiative transitions in quantum cascade lasers

A theoretical study has been made to compare the quantum efficiencies of in terwell and intrawell radiative transitions in quantum cascade lasers based on AlxGa1-xAs/GaAs technology. Radiative and nonradiative intersubband tra nsition rates were calculated for a range of temperatures between 4 and 300 K at an applied electric field of 4 kV cm-1 for structures designed to emi t in both mid-infrared and far-infrared frequency ranges. It is found that the internal quantum efficiency of mid-infrared devices is a maximum for di agonal, or interwell, transitions. Conversely, for the far-infrared devices , the quantum efficiency is a maximum for vertical, or intrawell, transitio ns. (C) 1999 American Institute of Physics. [S0003-6951(99)01940-3].