Phase diagram for the quantum Hall effect in a high-mobility AlGaN/GaN heterostructure

The magnetoresistance behaviour of a high-mobility AlGaN/GaN heterostructur e has been studied at low temperatures under magnetic fields of up to 28 T. Clear dissipationless minima in the Shubnikov-de Haas curves, for both cyc lotron-split and spin-split Landau levels, have been observed. The temperat ure dependence of the widths of these minima have enabled a phase diagram f or breakdown of the integer quantum Hall effect to be partially mapped out, and compared with similar results obtained for AlGaAs/GaAs heterojunctions . A distinctive feature of this sample is the variation of low-field electr on mobility between different voltage probes, and corresponding differences in the quantum Hall breakdown behaviour are seen.