Threshold current density calculations for far-infrared semiconductor lasers

We study theoretically the conditions for achieving lasing action at infrared and far-infrared wavelengths based on intersubband transitions in semiconductor quantum well structures, taking into account resonant tunnelling and intersubband absorption-emission processes. Analysis of optical losses in the semiconductor quantum well structures reveals that a reasonably low threshold current density in the range of 1-5 kA cm -2 is achievable for room temperature lasing at emission wavelength of lambda =60 mu m. A significantly higher threshold current density of 40-50 kA cm -2 is required for lasing at lambda =10 mu m.