Numerical analysis and optimization of device parameters for external quantum efficiency improvement in quantum cascade lasers

This research work evaluates the role of the parameters that impacts the optical external efficiency in Quantum Cascade Lasers (QCLs). QCLs fabricated from GaAlAs and emitting light at 9µm is chosen for the work. The Optical External Efficiency (OEE) is computed using three level rate equations that describing the carrier number and photon number variation in the laser cavity. The effect of length of lasing cavity, mirror reflectivity, optical confinement factor, and waveguide losses on optical external efficiency is explored in detail. From the analysis, it is evident that OEE reduces with increase in length of the lasing cavity, increases with increase in optical confinement factor, decreases with increase in mirror reflectivity and reduces when the waveguide losses increase. The optimum value of the parameters described is considered for maximizing the laser’s optical external efficiency. Maximum OEE of 19.41%, 20.41%, 19.49%, and 29.21% are obtained when the length of the lasing cavity, optical confinement factor, mirror reflectivity, and waveguide losses are varied individually. Numerical simulations provide optimum parameter values of L=1mm, Γ=0.45, R=0.25 and αw=10 cm−1, leading to a maximum OEE of 29.54% for the device under consideration which is higher than all the OEE values obtained under each criterion.