Kiyohito Yokoi

Single-Gated Single-Electron Transfer in Nonuniform Arrays of Quantum Dots

Single-electron transfer in single-gated one-dimensional quantum dot arrays is investigated statistically from the viewpoint of robustness against parameter fluctuations. We have found numerically that inhomogeneous quantum dot arrays formed in doped nanowires exhibit single-electron transfer over a wide range of parameters. This confirms our frequent experimental observation of single-electron transfer in doped-nanowire field-effect transistors. The most important result in this work is that three-dot arrays with small-large-small dot size distribution always allow single-electron transfer even if dot sizes fluctuate. This structure is, we believe, most promising for fabricating devices with high immunity against structural fluctuations on the nanometer scale. On the basis of these findings, we propose methods to fabricate high-yield single-electron transfer devices.

Single-Electron Transfer by Inter-Dopant Coupling Tuning in Doped Nanowire Silicon-on-Insulator Field-Effect Transistors

We demonstrate tunable single-electron turnstile operation in doped-nanowire silicon-on-insulator field-effect transistors. In these structures, electron transport occurs through dopant-induced quantum dots. We show that the substrate silicon can be used as a back gate to modulate the inter-dot coupling, which dictates the overlap between Coulomb domains in the charge stability diagrams of these devices. Since this overlap is a necessary requirement for single-electron turnstile, this procedure allows the optimization of the conditions for single-electron turnstile in doped-nanowire field-effect transistors.

Electrical control of capacitance dispersion for single-electron turnstile operation in common-gated junction arrays

We have studied single-electron turnstile operation in common-gated one-dimensional arrays of four tunnel junctions (three dots) having inhomogeneous junction capacitances. Analytical calculations show that the source-drain voltage range with a current plateau due to single-electron turnstile operation is increased when the outer two tunnel capacitances are adjusted to be smaller than the inner ones. In fact, we have demonstrated in phosphorous-doped silicon-on-insulator field-effect transistors (FETs) that back-gate voltage works to assist the turnstile operation, which is primarily ascribed to electrical control of junction capacitance dispersion, i.e., reduction in outer junction capacitances. As a result, postfabrication control of capacitance dispersion in multijunction FETs can be achieved, resulting in successful turnstile operation.

Tunable Single-Electron Turnstile Using Discrete Dopants in Nanoscale SOI-FETs

An individual dopant atom may become the active unit of future electronic devices by mediating single-electron transport in nanoscale field-effect transistors. Single dopants can be accessed electrically even in a dopant-rich environment, offering the opportunity to develop applications based on arrays of dopants. Here, we focus on single-electron turnstile operation in arrays of dopant-induced quantum dots realized in highly-doped nanoscale transistors. We show that dopant-based single-electron turnstile can be achieved and tuned with a combination of two gates and we indicate guidelines for further optimization.

Control of single dopants in the electron conduction path in SOI doped-nanowire FETs

We demonstrated that in SOI-PETs with doped-nanowire channel, both top gate and back gate can be used for adjusting the potential profile. New diamonds correspond to addition of dopants in the conduction path. Control of the conduction path with single-dopant accuracy allows the optimization of the dopant-induced QD structure. One possible application is toward improving the controllability of single-electron transfer in otherwise naturally disordered dopant arrays.

Single-Electron Transfer by Controlling the Dopant-Induced Quantum Dot Landscape

1. Single-electron transfer devices Single-electron devices (SEDs) have the capability of operating with individual charges, which makes them promising candidates for future electronics. 1 Among SEDs, an important category is formed by single-electron transfer devices, able to transfer elementary charges synchronized with external voltage pulses. Some design schemes have been already proposed based on precisely defined quantum dot (QD) arrays. The original single-electron turnstiles and pumps transfer electrons one-by-one during every cycle of one or, respectively, several ac gate voltages applied simultaneously to a 1D array of metallic QDs. Achieving such capabilities in semiconductor devices is essential for practical applications. In this direction, single-dot SEDs have been demonstrated to work as turnstiles and pumps by an appropriate control of the dot-lead coupling by ac-gates. 2-4

“Manipulation of single-electrons in Si nanodevices

Recently, we are entering a new stage of electronics, in which time-controlled transport of individual electrons can be achieved by using nanodevices, so-called single-electron tunneling devices. Also, it is recognized that single-electron transport is highly sensitive to ultimately small environmental charges such as a photogenerated electron and a doped ion, leading to a new paradigm in electronic devices working with a few elemental particles, i.e., electrons, phonons and ions.