Electron scattering spectroscopy by a high magnetic field in quantum cascade lasers

We present a detailed experimental and theoretical study of a $\mathrm{GaAs}∕\mathrm{AlGaAs}$ mid-infrared quantum cascade laser (QCL) under a strong magnetic field. The emitted power and the magnetoresistance show strong oscillations as a function of $B$, due to a magnetic field modulation of the lifetime of the upper state of the laser transition. The analysis of these oscillations shows a modulation of the electron lifetime due to inelastic (LO-phonon emission) and elastic scattering mechanisms. We show that at low temperature, the interface roughness scattering is the most efficient elastic relaxation mechanism; it becomes dominant whenever LO-phonon emission is inhibited by the magnetic field. By comparing experimental and theoretical results, we are able to estimate the relative weight of elastic and inelastic scattering. The magnetic field is thus a powerful spectroscopic tool to study the scattering mechanisms in QCL active regions.