Side-by-side existence of the quantum Hall effect and the magnetic-field-induced metal-insulator transition

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The authors report on a study of magnetotransport in a sheet of Si-donor impurities in MBE-grown GaAs. For densities in the 10 12 cm -2 range both the quantum Hall effect and magnetic freeze out are shown to occur. They point out the possibility of tuning the onset of the magnetic freeze out with respect to a given magnetic filling factor by selecting different donor densities. It has been proved that the quantum Hall effect can be investigated in semiconductor materials without the need of a confining hetero-barrier.