Interdiffusion limiting on self-consistent optical gain in terahertz quantum cascade lasers

Abstract

In this study, the physical picture of imperfect interfaces is characterized by two terms of in-plane roughness and out-plane interdiffusion. The corresponding scattering is quantified using the nonequilibrium Green’s function model by setting an additional self-energy, and then the impact of scattering strength on GaAs/Al0.3Ga0.7As 2-well terahertz quantum cascade laser performance is investigated. It shows that the interdiffusion scattering term can lead to a maximum reduction of approximately 30% in self-consistent optical gain at a temperature of 300 K. The decrease of population inversion, rather than the broadening linewidth of radiation transition, is the primary factor contributing to the gain degradation. By excluding the effect of band structure deformation caused by interdiffusion in advance, the main cause for the reduction in population inversion is identified as the decoherence of resonant-tunneling injection resulting from interdiffusion scattering.