Silicon Single-Electron Pump and Turnstile: Interplay with Crystalline Imperfections
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Silicon Single-Electron Pump and Turnstile: Interplay with Crystalline Imperfections Yukinori Ono1, Akira Fujiwara1, Yasuo Takahashi2, and Hiroshi Inokawa1 1NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan 2Graduate School of Information Science and Technology, Hokkaido University, Sapporo, Hokkaido, 060-0814, Japan ABSTRACT The single-electron device (SED), which has quantum dot(s), or island(s) in its core, enables the control of electron motion on the level of an elementary charge. The single-electron pump and turnstile are members of the SED family and enable single-electron transfer synchronized with the gate clock. They have the potential for extremely low error rates of electron transfer and are thus expected to be building-block devices for future information processing and electrical metrology. We have been pursuing the fabrication of Si-based SEDs using CMOS technology with the help of electron-beam lithography and have recently demonstrated a Si single-electron pump and turnstile. They are composed of one Si quantum dot and two tiny MOS gates and have dramatically increased the operation temperatures, which opens up the possibility of the practical use of the pump and turnstile. Another path to realizing single-electron transfer, which we will discuss here, might be to use a localized state in the Si bandgap instead of quantum dots. The localized states could in principle be donor/acceptor levels or any other states created by crystalline imperfections. They are free from the problem of the critical size control of the quantum dots, which might lead to a new era of single-electronics in combination with the rapidly developing research field of “dopant engineering”. INTRODUCTION - development of single-charge transfer devices In this article, we discuss single-charge transfer with a gate clock, which means the transfer of just a single charge during one cycle of an ac gate voltage. The single-electron transistor (SET) [1-3], the most fundamental single-electron device, unfortunately does not have this ability. This is because the time interval of each transfer in the SET is uncontrollable due to the stochastic nature of the electron tunneling. In order to transfer single electrons synchronized with the gate clock, we need more sophisticated devices. Sometimes called single-charge transfer devices, they include single-electron pumps and single-electron turnstiles. In these devices, an electron is conveyed from the source to drain in one cycle of the gate clock. Thus, the generated current is equal to ef, where e is the charge on an electron and f the clock frequency. Owing to the accurate transfer, single-charge transfer devices are expected to be key components for future information processing and electrical metrology based on fundamental physical constants. The research on the single-charge transfer device started using Al-AlOx multiple junctions, and expanded to semiconductors of GaAs and Si. The first single-charge transfer device was r
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