Energy relaxation of magnetically confined electrons in quantum cascade lasers

By measuring the light emitted from a quantum cascade laser placed in a high magnetic field, we have investigated the energy relaxation of 0D magnetically confined electrons in the active quantum wells of the structure. The experiment consists of injecting electrons by tunnelling into one upper subband level and monitoring a resonant interaction with optical phonons produced by Landau tuning of subband energy levels. For this purpose, the upper level lifetime is probed by measuring the laser intensity as a function of magnetic field, under constant current bias values. Both the laser intensity and the bias voltage oscillate periodically with the reciprocal of the field. In addition, at high magnetic fields, the current threshold goes through deep minima at antiresonance values. The lifetime is then deduced and analyzed using the strong electron–phonon coupling scheme which is typically applied to quantum dots.