Single Electron Transistor Structure Research Articles

Sequential reduction of the silicon single-electron transistor structure to atomic scale

Here we present an original CMOS compatible fabrication method of a single-electron transistor structure with extremely small islands, formed by solitary phosphorus dopants in the silicon nanobridge. Its key feature is the controllable size reduction of the nanobridge in sequential cycles of low energy isotropic reactive ion etching that results in a decreased number of active charge centers (dopants) in the nanobridge from hundreds to a single one. Electron transport through the individual phosphorous dopants in the silicon lattice was studied. The final transistor structure demonstrates a Coulomb blockade voltage of ∼30 mV and nanobridge size estimated as . Analysis of current stability diagrams shows that electron transport in samples after the final etching stage had a single-electron nature and was carried through three phosphorus atoms. The fabrication method of the demonstrated structure allows it to be modified further by various impurities in additional etching and implantation cycles.

Observation of charge transport through CdSe/ZnS quantum dots in a single-electron transistor structure

We fabricated single-electron transistors (SETs) having CdSe/ZnS core-shell-type quantum dots (CdSe/ZnS-QDs) as a Coulomb island using a wet chemistry technique. The CdSe/ZnS-QDs were deposited onto Au electrodes with or without the assistance of a self-assembled monolayer of octane(di)thiols. The CdSe/ZnS-QDs were adsorbed onto the Au electrodes even without the interlayer of thiol molecules depending on the concentration of the CdSe/ZnS-QD solution. The electron-transport characteristics through the CdSe/ZnS-QDs were examined in an SET structure at 13 K. Coulomb blockade behavior with typical gate voltage dependence was clearly observed. The estimated charge addition energies of a CdSe/ZnS-QD ranged from 70 to 280 meV. Moreover, additional structures, including negative differential conductance, appeared in the stability diagram in the source-drain bias region beyond 100 mV; these structures are specific to single-charge transport through the discrete energy levels in the Coulomb island.

Current enhancement with alternating gate voltage in the Coulomb-blockade regime of a single-wall carbon nanotube

We investigated the current–voltage characteristics of a carbon nanotube in a single electron transistor structure with alternating gate voltage. A continuous current enhancement effect with increasing frequency of the applied gate voltage up to 13 MHz is reported. Assuming that I=nef, more than 1000 electrons are driven to flow across the source–drain channel at VDS=100 mV, 13 MHz of gate voltage (Vp-p=2 V) and T=1.8 K. The continuous current enhancement is explained by the broadening effect of the discrete energy levels of the finite-length carbon nanotube.

Coulomb oscillations based on band-to-band tunneling in a degenerately doped silicon metal-oxide-semiconductor field-effect transistor

We report Coulomb oscillations based on band-to-band tunneling through a valence band in silicon metal-oxide-semiconductor field-effect transistors. Degenerately p+-doped channel and n+-doped source/drain enables band-to-band tunneling, which can play a major role in the transport between the channel and source/drain. The formation of tunnel barriers and a quantum dot in a single-electron transistor structure originates from two p+–n+ tunnel junctions and a p+-doped channel with mesoscopic dimension, respectively. Coulomb-blockade oscillations with multiple peaks were clearly observed at liquid nitrogen temperature. Using the electrical and thermal characterization of the quantum dot, single-electron charging effect based on band-to-band tunneling is confirmed.

Theory on the Coulomb blockade and current–voltage characteristics in Tomonaga–Luttinger liquid C-SET

We propose a self-consistent microscopic theory of the Coulomb blockade in the capacitively coupled single-electron transistor structure with Tomonaga–Luttinger liquid island connected with FL electrodes at both ends (TLL C-SET). Candidates for the island of TLL C-SET are carbon nanotubes and quantum wires. In this theory, the charging effect and the Tomonaga–Luttinger nature are treated in a consistent manner by the open boundary bosonization technique with consideration of zero modes based on the theory of C-SET for Fermi liquid electrodes. Analytical expression of the tunneling current in TLL C-SET is obtained up to the lowest order with respect to the tunneling Hamiltonian for arbitrary environmental impedance and it reasonably describes current–voltage characteristics caused by Coulomb blockade in Tomonaga–Luttinger liquid. We show that, in the ultrasmall but finite Tomonaga–Luttinger liquid, interaction-dependent exponent of the power law has system size dependence in addition to contact- (bulk- or edge-) nature dependence.

Single-Electron Charging Phenomena in Nano/Polycrystalline Silicon Point Contact Transistors

Single-Electron Charging Phenomena in Nano/Polycrystalline Silicon Point Contact Transistors

A novel single-electron analog-to-digital converter

The ideal single-electron transistor has a folding I-V characteristic. Multi-threshold periodic transmitting function can be achieved by using a complementary single-electron transistor structure, which can be used to simplify the analog-to-digital(A/D) converter. A novel 3-bit A/D converter by using the complementary single-electron transistor structure has many advantages including a simple structure, high speed and low power.

Single-electron transistor structures based on silicon-on-insulator silicon nanowire fabrication by scanning probe lithography and wet etching

We propose a promising fabrication technology for single-electron transistors based on a silicon-on-insulator (SOI) nanowire fabricated by scanning probe lithography and KOH wet etching. The 10-nm-wide and 10-nm-high silicon nanowire is defined by scanning probe lithography and KOH wet etching process technology. Along the [100] direction on a (100) SOI silicon wafer, local oxidation was performed in ambient using highly doped Si cantilevers with a resistivity of 0.01–0.0025 Ω cm and a commercial atomic force microscope/scanning tunneling microscope instrument. Using the oxide pattern as a Si etching mask, the Si substrate was dipped in aqueous KOH solution, in which unoxidized regions are selectively etched by aqueous KOH orientation-dependent etching. The silicon nanowire was obtained by well-controlled overetching of 34 wt % at 40 °C for 50 s. The top gate, back gates and contact pads were defined by photolithography and dry etching. Statistics showing the reproducibility of this technique are also demonstrated.

Fabrication technique for nanometer-scale InAs quantum devices: Observation of quantum interference in Aharonov–Bohm rings and Coulomb blockade in quantum dots

We report an approach to the lateral confinement of electrons in InAs/AlSb single quantum wells. Using electron-beam lithography and reactive ion etching, we have fabricated conducting wires, rings, and dots with lateral dimensions ⩾50 nm. Characterization on narrow wires and rings indicates that the electron transport is in the quasiballistic regime at 4.2 K. The current–voltage characteristics of 70-nm-diam dots in single-electron transistor structures show the Coulomb gap and the Coulomb staircase features. These artificially patterned devices have an ultimate lateral dimension of a few nanometers, limited by the resolution of electron-beam lithography.

Self-formed quantum nano-structures by selective area MOVPE and their application to GaAs single electron devices

Novel quantum nano-structures which consist of quantum dots connected with quantum wires through tunneling barriers have successfully been fabricated using selective area metalorganic vapor phase epitaxy (SA-MOVPE) and have been applied to form single electron devices. GaAs/AlGaAs modulation doped heterostructures are grown on a GaAs (001) substrate partially masked with SiNx. A quasi-1 dimensional electron gas (Q-1DEG) is formed in a narrow wire-like opening, which has two prominences and a dent to modulate the channel width. From the transport properties, we confirm that a quantum dot and quantum wires connected through tunneling barriers, that is, a single electron transistor structure, is naturally formed in the part of the channel with modulated width. We will discuss the mechanism by which the dot and tunnel barriers are formed by SA-MOVPE.

Electrical And Microscopic Investigation Of E-Gun Evaporated Titanium Thin Films

ABSTRACTThe deposition rate of titanium films plays a determining role for possible fabrication schemes of metallic SET structures. Depending on this rate the resistivities display a striking difference in their temperature dependence which is attributed to their different crystal structure as analyzed by transmission electron-beam microscopy. In addition a sharp rise in resistivity occurs below a critical thickness in films deposited at slow rates. This sharp increase can be used in combination with a step induced thinning to form tunnel junctions for single electron transistor structures.

Fabrication and properties of dot array using electron-beam-induced deposition

Electron-beam(EB)-induced deposition using precursor molecule of WF6 is applied to making metal/insulator/metal tunnel junctions for single electron transport devices. The SiO2 substrate pre-treated by oxygen plasma is contaminated with hydro-carbon material and the deposits show rapid decrease in resistance with the increase in EB dose and higher resistivity of about 100 Ω cm at 300 K which decreases by 20% at 130 K. In contrast, the thickness of deposits on clean substrates is 120 as small as the case of contaminated substrate for the same exposure dose. Also deposits with a lower resistivity of 4×10−3 Ω cm can be obtained. Under such deposition conditions, single electron transistor structure is fabricated which is composed of several dots connected to single line deposits with deposits for gate electrode 300 nm distant from the dot region. The source-drain voltage dependence of source current for 7 dots with 10 nm pitch exhibits Coulomb blockade characteristics at 12 K.