Single-electron pumping in common-gate triple-dot devices with arbitrary asymmetric gate capacitance distributions
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Single‑electron pumping in common‑gate triple‑dot devices with arbitrary asymmetric gate capacitance distributions Shigeru Imai1 · Reon Takanoya1 Received: 19 March 2020 / Accepted: 18 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Single-electron pumping in common-gate triple-dot devices is examined for arbitrary asymmetric gate capacitance distributions. Here, the ratio of the three gate capacitances is assumed to be a + d/2:1:a − d/2, where a and d are arbitrary positive real numbers. To ensure that pumping occurs, the gate voltage should be swung such that the set of excess electron numbers in the three dots is (ns, nc, ns) at low gate voltage and (ns, nc + 1, ns) or (ns + 1, nc − 1, ns + 1) at high gate voltage, where ns and nc are arbitrary integers. Moreover, (a, d) should be within a region that depends on the set of excess electron numbers at high and low gate voltages. Thus, the regions for pumping in the a–d plane are revealed. The absolute value of the bias voltage for pumping is limited to a maximum value, called the critical voltage. The critical voltage is also demonstrated as a function of a and d. The largest critical voltage obtained in this study is 2.5 times that reported in previous work for common-gate triple-dot devices. Keywords Single-electron pumping · Common-gate triple-dot structure · Stability regions · Coulomb blockade
1 Introduction Single-electron (SE) transfer devices [1] enable digital circuits to treat an SE as the smallest unit of information. In particular, SE pumping devices have a unique characteristic: an SE can be transferred to a negatively or zero-biased electrode. Various kinds of SE pumping devices have been reported [2–6]. These devices require at least two separate gate electrodes and two gate voltages (two alternating voltages or one alternating voltage and one constant voltage) to control island potentials or tunable tunnel barriers. In contrast, single-common-gate multidot SE devices [7–10] can work with only one gate voltage, and they have been examined by means of simulations [11–13] and analytical approaches [14–20]. We analytically demonstrated discrete SE transfer in common-gate triple-dot and quadruple-dot SE devices [21–25]. Furthermore, we introduced asymmetry into the gate capacitance (Cg) distribution in common-gate SE devices and demonstrated SE pumping
* Shigeru Imai [email protected] 1
Department of Electrical and Electronic Engineering, Ritsumeikan University, Kusatsu, Shiga 525‑8577, Japan
using only one alternating gate voltage without an additional constant gate voltage [26, 27]. The fabrication of these asymmetric structures requires precise control of the dot sizes and distances. This control has been achieved via the adsorption of size-controlled Au nanoparticles covered by self-assembled monolayers in the fabrication of single-dot and double-dot SE transistors, but their structures were considerably symmetric [28–30]. Asymmetric multidot structures could be fabricated by means of “recognit
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