ABSTRACT
In this work we present a method to measure the energy of the phonon modes responsible for non-radiative energy relaxation of electrons in the active zone of quantum cascade lasers (QCLs). The method is based on the analysis of the oscillation patterns of QCL emission intensity as a function of magnetic field applied along the growth direction. This technique is applied to both GaAs/AlGaAs QCLs (with Al concentration in the barriers of 33% and 45%) and to In0.73Ga0.27As/AlAs shortwavelength QCLs. We demonstrate that in the case of the GaAs/Al0.45Ga0.55As QCL, the relaxation via AlAs-like LO phonon can be significant. We further show that in case of the In0.73Ga0.27As/AlAs QCL, in spite of the high Al concentration in the barriers and the low GaAs contents in the wells, the non-radiative energy relaxation occurs principally via GaAs-like or InAs-like (or mixed modes) phonon emission, while a clear signature of AlAs-like phonons is not observed.
