Study of design-dependent electroluminescence linewidth of quantum cascade lasers

Electroluminescence linewidth is an important characteristic of quantum cascade lasers (QCLs) because the gain and the emission spectra of QCLs significantly depend on electroluminescence linewidth. Electroluminescence linewidth depends on the different intra-subband and inter-subband electron scattering mechanisms. Since the electron scattering rates due to different mechanisms vary when the applied electric field, temperature, and the quantum mechanical design vary, so does the electroluminescence linewidth of QCLs. In this work, we have studied the change in electroluminescence linewidth of QCLs when the quantum mechanical design and the material composition vary. We find that the linewidth of QCLs with diagonal lasing transition is greater than the linewidth of QCLs with vertical lasing transition; the linewidth of QCLs with strain-compensated material system is greater than the linewidth of QCLs with lattice-matched material system; and the linewidth of QCLs built on InGaAs/InAlAs material system is greater than the linewidth of QCLs built on GaAs/AlGaAs material system.