Filling-factor-dependent cyclotron mass in space-charge layers on GaAs

We report frequency-domain studies of cyclotron resonance in electron space-charge layers on GaAs. We observe variations of the cyclotron mass correlated with the filling factor. This is discussed in terms of conduction-band nonparabolicity, spin splitting of the Landau levels, and filling-factor-dependent screening of the electron–optical-phonon interaction. In samples with mobilities lower than 5×${10}^5$ ${\mathrm{cm}}^2$/V s there are line-shape anomalies with characteristics of anti-level-crossing that do not scale with the filling factor but depend on the electron density itself.