Yoshiyuki Kawata

Integration of Tunnel-Coupled Double Nanocrystalline Silicon Quantum Dots with a Multiple-Gate Single-Electron Transistor

We report on integration of double nanocrystalline silicon quantum dots (nc-Si QDs) of approximately 10 nm in diameter onto the multiple-gate single-electron transistor (SET) used as a highly-sensitive charge polarization detector. The SET with a single charging island is first patterned lithographically on silicon-on-insulator, and the multiple-gate bias dependence of the Coulomb current oscillation is characterized at 4.2 K. The coupling capacitance parameters between the SET charging island and the multiple-gate are estimated and compared with those obtained by using the three-dimensional capacitance simulation. Double nc-Si QDs are then deposited in the immediate vicinity of the charging island of the SET by using the very-high frequency plasma deposition technique. We perform the single-electron circuit simulations and demonstrate that only ±e charge polarization of the double QDs can be sensed as a shift of the Coulomb oscillation peaks.

New Design Concept and Fabrication Process for Three-Dimensional Silicon Photonic Crystal Structures

We propose a new design concept and a fabrication process for three-dimensional (3D) silicon photonic crystals on a 100 nm scale that does not require any alignment processes. The elemental technique used in this process is two directional electrochemical etching processes at a particular magnetic field. First, we have performed photonic band calculation and estimated device parameters to obtain the maximum photonic band gap in the visible range centered at around 800 nm. Next, we have experimentally observed the formation of a two-dimensional periodic pore with a diameter of 80 nm and an aspect ratio above 80 on an n+ (100) silicon substrate. Finally, we have fabricated 3D microstructures by two directional etching processes. A clear directionality for the pore formation was observed in two directions, showing the possibility of projecting the patterns formed on the slope to the side of the wafer. These fundamental etching processes can be applied to the fabrication of 3D photonic crystals in the visible range without any alignment processes.

Study of Single-Charge Polarization on a Pair of Charge Qubits Integrated Onto a Silicon Double Single-Electron Transistor Readout

This paper reports on integration of two silicon (Si) charge quantum bits (qubits) and series-connected double single-electron transistors (DSETs) as readout for the first time. We design and fabricate the DSETs composed of double quantum dots (DQDs) connected in series with two side gates patterned on a silicon-on-insulator substrate. The individual SETs are sufficiently sensitive to detect single-charge polarization on the adjacent charge qubits. The fabricated DSETs are characterized at a temperature of 4.2 K by changing the gate voltages applied to the two side gates. The measured Coulomb oscillation characteristics exhibit a clearly defined hexagon pattern, manifesting that the patterned DQDs of the DSETs, indeed, act as interacting charging islands. These results agree very well with the results of equivalent circuit simulation combined with 3-D capacitance simulation. Furthermore, we simulate how single-charge configurations on two charge qubits are sensed with the DSETs by using the measured electrical characteristics for the DSET and the equivalent model. Finally, the scaling-up properties of the proposed system to multiple single-electron transistors (MSETs) are discussed by simulating triple single-electron transistors (TSETs) with triple qubits.

Observation of Quantum Level Spectrum for Silicon Double Single-Electron Transistors

Double quantum dots (DQDs) have been studied as attractive candidates for charge qubits. Initially, GaAs-based DQDs formed by means of surface gates depletion were studied because many parameters are tunable after their fabrications [1]. However, silicon-based DQDs are more promising for charge qubits because of the absence ofpiezoelectric electron-phonon coupling, and the effect of phonon localization [2]. Furthermore, to integrate Si multiple charge qubits and a readout device in a small footprint, a series-connected double dots transistor has recently been proposed and studied [3]. The readout is called as double single-electron transistors (DSETs) and facilitates to detect the single-charge polarizations on the adjacent double qubits efficiently [4]. The other advantage of DSETs is that both two SETs act as feedback transistors to each other to compensate the random fluctuation noise.

A new design of nanocrystalline silicon optical devices based on 3-dimensional photonic crystal structures

We propose a new design of nanocrystalline silicon optical devices which are based on control of electromagnetic fields, electronic states, as well as the phonon dispersion of size-controlled silicon quantum dots.

Observation of quantum level spectrum for silicon double single-electron transistors

Double quantum dots (DQDs) have been studied as attractive candidates for charge qubits. Initially, GaAs-based DQDs formed by means of surface gates depletion were studied because many parameters are tunable after their fabrications [1]. However, silicon-based DQDs are more promising for charge qubits because of the absence ofpiezoelectric electron-phonon coupling, and the effect of phonon localization [2]. Furthermore, to integrate Si multiple charge qubits and a readout device in a small footprint, a series-connected double dots transistor has recently been proposed and studied [3]. The readout is called as double single-electron transistors (DSETs) and facilitates to detect the single-charge polarizations on the adjacent double qubits efficiently [4]. The other advantage of DSETs is that both two SETs act as feedback transistors to each other to compensate the random fluctuation noise.

Detection of single-charge polarisation in silicon double quantum dots by using serially-connected multiple single-electron transistors

We investigate novel serially-connected multiple single-electron transistors (MSETs) as a single-charge polarisation readout for silicon integrated charge qubits. We first design and analyse the double single-electron transistors (DSETs) in which double quantum dots are connected in series with two side gates. We show that the DSETs are sufficiently sensitive to distinguish all the single-charge polarisation states on the two charge qubits integrated adjacently. We also show the scalability of the MSETs by extending our analysis to a scaled-up system of serial triple single-electron transistors (TSETs) integrated with triple charge qubits. Finally we fabricate the DSETs with double charge qubits on the silicon-on-insulator substrate and observe hysteresis in the Coulomb oscillations of the tunnel current at temperature of 4.2 K, which are attributable to the change of polarisation in the double charge qubits.

Strongly coupled multiple-dot characteristics in dual recess structured silicon channel

Silicon single electron transistors were fabricated by using the highly doped silicon channel with dual recess structure along with two recess gates and one central island gate as a pattern. The transition of Coulomb oscillation characteristics from a single dot to a strongly coupled multiple dot was demonstrated for the different oxidation times and recess dimensions. The multiple-dot characteristic in the longer post lithography oxidized sample is attributed to the formation of a single dot in each recess due to the stress induced pattern-dependent oxidation, which leads to multiple dot in the channel. The temperature variation measurement, which was performed after two thermal cycling of the same sample to 20 and 4.2?K with 1?month gap, revealed the highly stable nature of the multiple-dot device transport characteristics. The multiple-dot device can also be operated as a unique nonlinear tunable resistance single electron transistor

Study of Single-Charge Polarization on two Charge Qubits Integrated onto a Double Single-Electron Transistor Readout

Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan Phone: +81-5734-3854 FAX: +81-5734-2542 e-mail: kawata@neo.pe.titech.ac.jp School of Electronics and Computer Science, University of Southampton, Southampton, UK Department of Physical Electronics, Tokyo Institute of Technology, Tokyo, Japan SORST-JST (Japan Science and Technology Agency)

Fabrication of silicon 3D photonic crystal structures in 100nm scale using double directional etchings method

We have reported periodic pore formation with diameter in 80 nm and aspect ratio above 250 on N+(100) silicon substrate and demonstrated the fabrication of silicon 3-dimensional microstructures by applying double directional etchings method.