Improved large optical cavity design for 10.6 μm (Al)GaAs quantum cascade lasers

We have developed an improved waveguide design for 10.6 μm (Al)GaAs quantum cascade lasers based on a large optical cavity. With the optical confinement based on the free-carrier plasma effect we accurately evaluate the complex dielectric constant as a function of doping densities of the GaAs waveguide layers. Free-carrier absorption losses and confinement factors are simulated and compared with experimental results. An improved design was obtained by varying the doping profile of the large optical cavity resulting in a 30% reduced threshold current density of 3.4 kA cm^-2 at 77 K heatsink temperature.