The origin of switching noise in GaAs/AlGaAs lateral gated devices

TL;DR

This study investigates the origin of switching noise in GaAs/AlGaAs quantum devices, showing that leakage current through the Schottky barrier causes noise, and that bias cooling reduces this noise by modifying the doping and tunneling barriers.

Contribution

The paper introduces a model linking switching noise to electron tunneling through the Schottky barrier and demonstrates noise reduction via bias cooling in GaAs/AlGaAs devices.

Findings

Bias cooling reduces switching noise significantly.

Leakage current of about 10^{-20} A detected into quantum dots.

Asymmetric gate bias increases noise, consistent with the model.

Abstract

We have studied the origin of switching (telegraph) noise at low temperature in lateral quantum structures defined electrostatically in GaAs/AlGaAs heterostructures by surface gates. The noise was measured by monitoring the conductance fluctuations around $e^2/h$ on the first step of a quantum point contact at around 1.2 K. Cooling with a positive bias on the gates dramatically reduces this noise, while an asymmetric bias exacerbates it. We propose a model in which the noise originates from a leakage current of electrons that tunnel through the Schottky barrier under the gate into the doped layer. The key to reducing noise is to keep this barrier opaque under experimental conditions. Bias cooling reduces the density of ionized donors, which builds in an effective negative gate voltage. A smaller negative bias is therefore needed to reach the desired operating point. This suppresses tunnelling from the gate and hence the noise. The reduction in the density of ionized donors also strengthens the barrier to tunneling at a given applied voltage. Support for the model comes from our direct observation of the leakage current into a closed quantum dot, around $10^{-20} \mathrm{A}$ for this device. The current was detected by a neighboring quantum point contact, which showed monotonic steps in time associated with the tunneling of single electrons into the dot. If asymmetric gate voltages are applied, our model suggests that the noise will increase as a consequence of the more negative gate voltage applied to one of the gates to maintain the same device conductance. We observe exactly this behaviour in our experiments.