Impurity cyclotron resonance in type-I (GaAs)n/(AlAs)n superlattices

We have carried out measurements of cyclotron resonance (CR) in type-I (GaAs)n/(AlAs)n superlattices (SLs) applying pulsed high magnetic fields up to 150 T. Two types of peaks have been observed in CR signals; one originates from a transition between Landau levels of free electrons, and the other from transition between impurity levels. The free-electron CR signals are dominant at room temperature, and the impurity CR signals become large as temperature decreases. From the peak position of CR spectra, at room temperature, the effective mass of the electron in (GaAs)n/(AlAs)n SL is deduced. To analyze the impurity transition in high magnetic fields, we have calculated the impurity levels in the SLs using the variational method assuming a single quantum well for simplicity. In spite of a very simple model, the calculated results are in good agreement with the CR results of type-I (GaAs)n/(AlAs)n SLs.