Cyclotron resonance of electrons in a narrow GaAs/(Ga,Al)As quantum well: Polaron effects and non-parabolicity

Cyclotron resonance of electrons in a GaAs/Ga0.64Al0.36As multi-quantum-well sample with 2.2 nm well width is reported, in magnetic fields up to 19 T applied perpendicular to the well planes. The resonances are observed by using optical pumping to populate the electron subband of the wells, which are nominally undoped. In addition, inter-band magneto-optical experiments were performed on the same sample, and the transitions are fitted using a calculation of the excitonic Landau level transitions: this gives a separate check on the electron band non-parabolicity. It is found that the band non-parabolicity of the electrons for motion perpendicular to the well plane (i.e. confinement) is much smaller than the band non-parabolicity due to motion in the well plane (i.e. cyclotron motion): the latter is close to the recently deduced values for bulk GaAs. The polaron contribution to the non-parabolicity is found to be almost negligibly enhanced over the predicted three-dimensional value.