Analytical Study on a Single-Electron Device with Three Islands Connected to One Gate Electrode

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We have studied a triple-dot single-electron device that includes four series tunnel junctions connecting a source, three islands and a drain, and three capacitive couplings connecting a gate to the three islands. Algebraic solutions for voltage distribution and Coulomb blockade (CB) conditions were derived for the triple-dot device with a homogeneous tunnel capacitance $C_{\text{j}}$ and a homogeneous gate capacitance $C_{\text{g}}$. With the help of the established formulas, stability diagrams for the device were drawn and device operating modes were investigated in detail. Stability regions for $\mathbf{n} \equiv (n_{1}, n_{2}, n_{3}) = (0, 0, 0)$ and $\mathbf{n} = (0, 1, 0)$ have the shapes of a rhombus and a kite, respectively, and are located along the $V_{\text{g}}$ axis. They overlap and a cycle of alternating gate voltage can transfer a single electron from the source to the drain through the islands, that is, the device works as a single-electron turnstile even though it has uniform capacitances. The turnstile operation is possible for any $C_{\text{g}}/C_{\text{j}}$ ratio. If $C_{\text{g}}/C_{\text{j}}$ is less than $\sqrt{2}-1$, stability regions for $\mathbf{n} = (1, 0, 0)$ and $\mathbf{n} = (0, 0, 1)$ exist but they do not affect the turnstile operation.
2009-12-25