Gating a Quantum Dot through the Sequential Removal of Single Electrons from a Nanoscale Floating Gate

Abstract

We use the tip of an atomic force microscope (AFM) to charge floating metallic gates defined on the surface of a Si/SiGe heterostructure. The AFM tip serves as an ideal and movable cryogenic switch, allowing us to bias a floating gate to a specific voltage and then lock the charge on the gate by withdrawing the tip. Biasing with an AFM tip allows us to reduce the size of a quantum dot floating-gate electrode down to approximately 100nm. Measurements of the conductance through a quantum dot formed beneath the floating gate indicate that its charge changes in discrete steps. From the statistics of the single-electron leakage events, we determine the floating-gate leakage resistance R∼10^{19}Ohm—a value that is immeasurable by conventional means.