Doping in quantum cascade lasers. II. GaAs/[Al.sub.0.15][Ga.sub.0.85]As terahertz devices

The performances of GaAs/[Al.sub.0.15][Ga.sub.0.85]As terahertz quantum cascade lasers based on a bound-to-continuum transition are examined as a function of injector doping. A linear dependence between threshold current and doping is observed and it has agreed well with the expected increase of waveguide losses due to free carrier absorption.