Reduction of charge noise in shallow GaAs/AlGaAs heterostructures with insulated gates*

Low-frequency charge noise is ubiquitous in low dimensional devices. A high level of charge noise prevents stable operation of devices and can be a severe problem for many applications. We observe that GaAs/AlGaAs QPC devices with an Al2O3 dielectric between the metal gates and semiconductor exhibit significantly lower charge noise compared to devices with only Schottky gates and no dielectric. Additionally, the devices with Schottky gates exhibit drift over time towards lower conductance, while the devices with the dielectric drift towards higher conductance. Temperature dependence measurements suggest that in devices with Schottky gates noise is dominated by tunneling from the gates to trap sites in the semiconductor, and when this mechanism is suppressed by inclusion of a dielectric, thermally activated hopping between trap sites becomes the dominant source of noise.