Anomalous behavior of cyclotron resonance in GaAs/Al0.28Ga0.72As high-electron-mobility transistor structures

Infrared cyclotron-resonance measurements were obtained for a two-dimensional electron gas (2DEG) in GaAs/${\mathrm{Al}}_{0.28}$ ${\mathrm{Ga}}_{0.72}$As high-electron-mobility transistor structures at 5 K. The relaxation time and concentration of the 2DEG were extracted from fitting the cyclotron-resonance transmission spectra with a transmissivity equation based on a Drude-type model. The effective mass, relaxation time, full width at half maximum, amplitude, total integrated absorption, and the concentration (${\mathit{n}}_{\mathit{s}}$) of the 2DEG are shown to oscillate as a function of the magnetic field. The total integrated absorption of the cyclotron resonance and the ${\mathit{n}}_{\mathit{s}}$ value extracted from fitting the transmissivity equation to the cyclotron-resonance spectra exhibit similar behavior as the magnetic field is increased. The oscillation of ${\mathit{n}}_{\mathit{s}}$ with the magnetic field suggests that screening effects are not negligible. Furthermore, the oscillations of the above parameters seem to provide qualitative information about the influence of the ion-electron interactions on the far-infrared cyclotron-resonance spectra.