QUANTUM HALL SAMPLES PREPARED BY HELIUM-ION IMPLANTATION

We have produced GaAs/GaAlAs heterostructure-based quantum Hall samples with a wide range of electron mobilities using ion implanatation. The purpose has been to optimize the samples for use in metrology. In particular, we have studied the critical current, below which the accuracy of the quantum Hall resistance is adequate for metrological use, and the non-ohmic behavior of our samples for large currents in the vicinity of a quantum Hall plateau. Opposite to expectation, we found that on a critical current versus magnetic field plot the sample with the highest mobility (100 T-1) was definitely the best in spite of the fact that the plateau on a coarser scale was wider.