Analysis of polaron effects in the cyclotron resonance ofn-GaAs and AlGaAs-GaAs heterojunctions

Cyclotron resonance (CR) was measured at high magnetic fields in three-dimensional bulk n-GaAs and in the two-dimensional (2D) electron system of an AlGaAs-GaAs heterojunction, at a number of far-infrared laser lines, up to energies close to the longitudinal optical phonon energy, ħ${\omega }_{\mathrm{LO}}$. A quantitative analysis of the CR as a function of magnetic field is presented, taking into account dimensionality, band nonparabolicity, and polaron effects. It is found that screening is important in 2D systems, and from an analysis of polaron effects in the CR of the AlGaAs-GaAs heterojunction, a value for the screening strength in a 2D electron system is obtained. Our analysis of data very close to resonance with the optical phonon shows that band nonparabolicity has to be included explicitly in the calculation of polaron corrections to obtain the proper asymptotic limit ħ${\omega }_{\mathrm{LO}}$ for the CR transition energy.