Nonlinear intersubband absorption coefficient in an AlxGa1−xAs/GaAs quantum cascade laser-like profile

Abstract

In this work we perform a theoretical study on the nonlinear intersubband absorption response in a quantum cascade laser (QCL) profile-like heterostructure that consists of a triple AlAs/GaAs quantum well. In particular, we investigate the role of the central quantum well width, as well as the electric and magnetic field effects, on the intersubband optical properties of the system. Results on the electronic structure arise within the framework of the effective mass, and parabolic band approximations. The calculation also takes into account the effective mass mismatch in the kinetic energy and magnetic potential energy terms, in order to investigate the importance of the position dependence of this parameter. The conduction band offset ratio was determined using the model solid theory, considering strain effects. The expression from which we calculate the nonlinear optical response comes from the third-order dielectric susceptibility derived within the compact density matrix formalism. In general we have obtained that, as a function of the central well width and the applied magnetic field strength, the light absorption coefficient can exhibit red- and blue-shifts. Meanwhile, in the case of the application of an electric field only blue-shifts are observed. The effective mass mismatch is more significant for small applied magnetic fields, due to the difference in the resonant peak found in the absorption coefficient. In all cases it is found that the third-order correction is significant in value.