Design optimization of quantum cascade laser structures at λ ∼ 11–12 µm

Abstract

AbstractBy a simulation optimization technique, we design In0.53Ga0.47As/In0.52Al0.48As quantum cascade laser (QCL) structures, based on a four‐quantum well (QW) active region. The design of QCL structures is performed by maximizing an objective function, i.e., $z_{{\rm UL}}^2 (1 - \tau _{\rm L} /\tau _{{\rm UL}} )\tau _{\rm U}$, related to the optical gain, including dipole matrix element ($z_{{\rm UL}}$) and population inversion between subbands. For a specific lasing wavelength, each barrier/well layer in the active region can be optimized to maximize the objective function, which results from the increase in the dipole matrix element and the reduction in the lifetime ratio of $\tau _{\rm L} /\tau _{{\rm UL}}$, by an iterative procedure. The optimized QCL structures are obtained for the target wavelengths from 11 to 12 µm by a step of 0.5 µm. For a QCL structure operating at λ = 11.98, it exhibits the maximized objection function of 6.30 ps‐nm2 with a large dipole matrix element under an electric field of 45 kV/cm. The influence of the percent variation of thickness in In0.53Ga0.47As and In0.52Al0.48As layers by the change in growth rate on the lasing wavelength and objective function is also investigated.