High-current effects in magnetotransport of two-dimensional electrons in GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As heterostructures

Nonlinear transport in GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As heterostructures was studied at high current densities in the strong-magnetic-field limit. The striking features in the transport characteristics result from breakdown of the integer quantum Hall effect (IQHE) and thermionic emission of hot electrons in the inversion layer of GaAs to the bypass layer of ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As. In narrow-channel devices, we observe a series of pronounced steps in the longitudinal resistance as a function of current or magnetic field. We show that these steps originate from localized breakdowns of the IQHE at different sections of the sample. (The nature of these steps was previously incorrectly attributed in the literature to a new quantization in electronic transport.) In addition, we report the observation of a strong negative differential resistance, realized exclusively at high magnetic fields. It results from an interplay between a real-space transfer of hot electrons in GaAs into the ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layer and the IQHE due to the cold electrons remaining in the inversion layer.