Abstract
Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Such information is not yet available for QDs made out of the new material graphene, where both substrate and edge states are known to have important effects. Here we show the 1/f noise for a microscopic graphene QD is substantially larger than that for a macroscopic graphene field-effect transistor (FET), increasing linearly with temperature. To understand its origin, we suspended the graphene QD above the substrate. In contrast to large area graphene FETs, we find that a suspended graphene QD has an almost-identical noise level as an unsuspended one. Tracking noise levels around the Coulomb blockade peak as a function of gate voltage yields potential fluctuations of order 1 μeV, almost one order larger than in GaAs/GaAlAs QDs. Edge states and surface impurities rather than substrate-induced disorders, appear to dominate the 1/f noise, thus affecting the coherency of graphene nano-devices.
Highlights
Charge noise is critical in the performance of gate-controlled quantum dots (QDs)
In contrast to large area graphene field-effect transistor (FET), we find that a suspended graphene QD has an almost-identical noise level as an unsuspended one
Suspended graphene flakes can yield a huge increase in low-temperature mobility approaching 200,000 cm[2] V21 S21 for carrier densities below 5 3 109 cm22 . 17,18 The charge noise of graphene field effect transistors (GFETs) can be suppressed by one order of magnitude when suspended from the substrate[11]
Summary
Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Such information is not yet available for QDs made out of the new material graphene, where both substrate and edge states are known to have important effects. Tracking noise levels around the Coulomb blockade peak as a function of gate voltage yields potential fluctuations of order 1 meV, almost one order larger than in GaAs/GaAlAs QDs. Edge states and surface impurities rather than substrate-induced disorders, appear to dominate the 1/f noise, affecting the coherency of graphene nano-devices. We used the wet-etching method[33,34] to fabricate suspended graphene nanoribbons These suspended nanoribbon devices behave to unsuspended ones and can be tuned to the Coulomb blockade region to form GQDs. By measuring the 1/f noise along Coulomb peaks, we can obtain the charge noise, corresponding to potential energy fluctuations, which increase linearly with temperature. We present a simplified model explaining how edge states rather than the substrate act as more important sources of charge www.nature.com/scientificreports noise in GQD devices, inferring that the elimination of edge states should be a key task for the future when exploiting graphene nanodevices
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