Electron-phonon interaction in quantum cascade structures probed by Landau level spectroscopy

In this work we present a method to study the energy of the phonon modes responsible for nonradiative energy relaxation of electrons in the active zone of quantum cascade lasers (QCLs). The method is based on the analysis of the oscillations pattern of QCLs emission intensity as a function of magnetic field applied along the growth direction. We studied first GaAs/AlGaAs QCLs with different Al concentration in the barriers (33% and 45%). We demonstrated that in the case of high Al concentration the relaxation via AlAs- like LO phonon can be significant. We have also shown that in case of In0.73Ga0.27As/AlAs short-wavelength QCL in spite of the high Al concentration in the barriers and the low GaAs contents in the wells, the nonradiative energy relaxation happens principally via GaAs-like or InAs-like (or mixed modes) phonon emission, while a clear signature of AlAs-like phonons was not observed.