We demonstrate that low-temperature illumination of a GaAs/AlGaAs Hall bar, partially covered by a split metal gate structure, results in the formation of a shallow barrier across the entire device, even in the point contact openings not directly covered by the gates. The minimum carrier density inhomogeneity is determined from the position of the anomalous Hall steps, which are observed even at zero gate voltage as a result of barrier formation. Our results suggest a substantial contribution to the carrier density inhomogeneity, implying that low-temperature illumination may considerably increase disorder in split gate nanostructures. References: 15
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