D. G. Hasko

University of Cambridge, Cambridge, England, United Kingdom

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Publications (214)452.92 Total impact

  • S. Fleming, W. I. Milne, D. G. Hasko
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    ABSTRACT: We investigate the use of a percolation-field-effect-transistor for the continuous weak measurement of a spatially Rabi oscillating trapped electron through the change in percolation pathway of the transistor channel. In contrast to conventional devices, this detection mechanism in principle does not require a change in the stored energy of the gate capacitance to modify the drain current, so reducing the measurement back-action. The signal-to-noise ratio and measurement bandwidth are seen to be improved compared to conventional devices, allowing further aspects of the dynamic behaviour to be observed.
    Applied Physics Letters 08/2013; 103(9). · 3.52 Impact Factor
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    ABSTRACT: It is widely reported that threshold voltage and on-state current of amorphous indium-gallium-zinc-oxide bottom-gate thin-film transistors are strongly influenced by the choice of source/drain contact metal. Electrical characterisation of thin-film transistors indicates that the electrical properties depend on the type and thickness of the metal(s) used. Electron transport mechanisms and possibilities for control of the defect state density are discussed. Pilling-Bedworth theory for metal oxidation explains the interaction between contact metal and amorphous indium-gallium-zinc-oxide, which leads to significant trap formation. Charge trapping within these states leads to variable capacitance diode-like behavior and is shown to explain the thin-film transistor operation.
    Applied Physics Letters 04/2013; 102(15). · 3.52 Impact Factor
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    ABSTRACT: A one electron-based operating half-adder, the smallest arithmetic block, has been implemented on silicon-on-insulator structure whose basic element is a nanoscale single-electron transistor (SET) with two symmetrical side-wall gates. Grayscale contour plots of the resulting cell output voltages exhibit the Coulomb blockade-induced periodic alternating high/low features. Their voltage transfer characteristics display typical Sum and Carry-Out functions for binary, multi-valued (MV), and binary-MV mixed input voltages. Moreover, the half-adder function converts into a subtraction mode by adjusting control gates of the SET element. This flexible multi-valued cell provides an arithmetic block for the SET MV logic family of high density integration, operating with ultra-low power.
    Applied Physics Letters 10/2012; 101(18). · 3.52 Impact Factor
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    ABSTRACT: Trapped electrons, located close to the channel of a transistor, are promising as data storage elements in non-classical information processing. Cryogenic microwave spectroscopy has shown that these electrons give rise to high quality factor resonances in the drain current and a post excitation dynamic behaviour that is related to the system lifetime. Using a floating poly-silicon gate transistor, single shot spectroscopy is performed to characterise the dynamic behaviour during excitation. This behaviour is seen to be dominated by the decay of the transient component, which gives rise to oscillations around the high quality factor resonance.
    Journal of Applied Physics 07/2012; 112(1). · 2.21 Impact Factor
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    ABSTRACT: We investigate the electrical transport properties of silicon nanowire arrays grown by Au catalyzed chemical vapor deposition, resulting in prominent Au nanoparticle sidewall decoration. dc electrical measurements show symmetric nonlinear I-V characteristics with a zero field conductivity temperature dependence consistent with nearest neighbor hopping. The characteristic energy for this temperature dependence is similar to the expected charging energy of the Au nanoparticles. The measured resistance is also dependent on the bias voltage history if large electric fields are applied. Random telegraph noise events at low temperature indicate that the measured resistance is dominated by a small number of electrons confined to a single nanowire in the array. With a fixed bias, the resistance can be influenced by indirectly coupled microwave radiation at low temperature. This results in a large number of high quality factor resonant features, indicating significant excitation lifetimes. The origin of these resonances is thought to be due to spatial Rabi oscillations of trapped electrons between pairs of trap sites located close to the channel. Such systems are promising for charge qubit-based quantum information processing.
    Journal of Applied Physics 06/2011; 109(11):113713-113713-4. · 2.21 Impact Factor
  • Source
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    ABSTRACT: We report on transport measurement performed on a room-temperature-operating ultrasmall Coulomb blockade devices with a silicon island of sub5 nm. The charge stability at 300K exhibits a substantial change in slopes and diagonal size of each successive Coulomb diamond, but remarkably its main feature persists even at low temperature down to 5.3K except for additional Coulomb peak splitting. This key feature of charge stability with additional fine structures of Coulomb peaks are successfully modeled by including the interplay between Coulomb interaction, valley splitting, and strong quantum confinement, which leads to several low-energy many-body excited states for each dot occupancy. These excited states become enhanced in the sub5 nm ultrasmall scale and persist even at 300K in the form of cluster, leading to the substantial modulation of charge stability.
    Nano Letters 03/2011; 11(4):1591-7. · 13.03 Impact Factor
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    ABSTRACT: We describe fabrication of sub-micron photonic bandgap structures on Si/SiO 2 optical waveguide, which could be used at X=1.54ltm. INTRODUCTION Control of the propagation of light using the photonic band gap (PBG) effect in photonic devices is the subject of intense international effort -[61 PBG materials are optical analogs of semiconductors. Main drive is towards making structures that modulate free photon dispersion as much as the same way as semiconductor crystal does for electrons. A high dielectric contrast material system is a fundamental requirement for the existence of a PBG. Silicon microphotonics, which uses Si over SiO 2 system, provides a large index difference (An= 2.0@1.54pm) between the core and the cladding of the guide. Because of the high confinement of the optical wave, the waveguide cross-section has been miniaturised. Strip waveguides with holes of 200nm diameter have been fabricated. The cross-section of the strip waveguide is 0.26x0.5 pm. We have addressed some of the important issues regarding fabrication. On the simulation front, we have used commercially available software Fimmprop3D for 2D simulation of the device. Figure l(a) and (b) shows the simulation results. Actual structure is shown in the inset of Figure l(b). High index contrast structures introduce a process problem because performance is limited by scattering loss from surface roughness. One important challenge towards realizing silicon microphotonics lies in making optically smooth structure to keep the scattering loss as low as possible. The dominant source of loss is the sidewall roughness scattering [7]. The increase is attributed to sidewall roughness created during the waveguide patterning process involving lithography and RIE.' We have proposed combined chlorine-fluorine based plasma as a reactive ion-etching recipe for silicon microphotonics. Extremely smooth photonic structures of feature size as small as 0.1pum have been made. FABRICATION PBG effect devices have been made using high-resolution lithographic and pattern transfer processes, which include electron beam lithography and reactive-ion-etching. The first step is the realisation of the plasma etch mask. The poor etch resistance of PMMA is serious limiting factor for pattern transfer. The problem has been overcome by using Al as a metal etch mask.
    MRS Online Proceeding Library 01/2011; 694.
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    ABSTRACT: The nanoscale morphology in polymer:PCBM based photovoltaic devices is a major contributor to overall device performance. The disordered nature of the phase-separated structure, in combination with the small length scales involved and the inherent difficulty of reproducing the exact morphologies when spin-coating and annealing thin blend films, have greatly hampered the development of a detailed understanding of how morphology impacts photo­voltaic device functioning. In this paper we demonstrate a double nano­imprinting process that allows the formation of nanostructured polymer:PCBM heterojunctions of composition and morphology that can be selected independently. We fabricated photovoltaic (PV) devices with extremely high densities (1014 mm−2) of interpenetrating nanoscale columnar features (as small as 25 nm; at or below the exciton diffusion length) in the active layer. By comparing device results of different feature sizes and two different polymer:PCBM combinations, we demonstrate how double imprinting can be a powerful tool to systematically study different parameters in polymer photovoltaic devices.
    Advanced Functional Materials 11/2010; 21(1):139 - 146. · 10.44 Impact Factor
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    ABSTRACT: A vertically aligned carbon nanotube mesh emitter array has been fabricated and tested, giving a current density of up to 1.5 A/cm2, and a threshold field of 1.5 V/μm for a current density 1 mA/cm2. Low temperature carbon nanotube growth is used to fabricate the carbon nanotube mesh emitter arrays significantly reducing the cost of the fabrication of large area electron emitters. This system exhibits ultralong lifetime.
    Applied Physics Letters 09/2010; 97(11):113107-113107-3. · 3.52 Impact Factor
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    ABSTRACT: An ultrasmall single-electron transistor has been made by scaling the size of a fin field-effect transistor structure down to an ultimate limiting form, resulting in the reliable formation of a sub-5 nm Coulomb island. The charge stability data feature the first exhibition of three and a half clear Coulomb diamonds at 300 K, each showing a high peak-to-valley current ratio. Its charging energy is estimated to be more than one order magnitude larger than the thermal energy at room-temperature. The hybrid literal gate integrated by this single-electron transistor combined with a field-effect transistor displays >5 bit multiswitching behavior at 300 K with a large voltage swing of ∼ 1 V.
    Applied Physics Letters 09/2010; 97(10). · 3.52 Impact Factor
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    ABSTRACT: The fabrication of very narrow metal lines by the lift-off technique, especially below sub-10 nm, is challenging due to thinner resist requirements in order to achieve the lithographic resolution. At such small length scales, when the grain size becomes comparable with the line-width, the built-in stress in the metal film can cause a break to occur at a grain boundary. Moreover, the line-width roughness (LWR) from the patterned resist can result in deposited metal lines with a very high LWR, leading to an adverse change in device characteristics. Here a new approach that is not based on the lift-off technique but rather on low temperature hydrogen reduction of electron-beam patterned metal naphthenates is demonstrated. This not only enables the fabrication of sub-10 nm metal lines of good integrity, but also of low LWR, below the limit of 3.2 nm discussed in the International Technology Roadmap for Semiconductors. Using this method, sub-10 nm nickel wires are obtained by reducing patterned nickel naphthenate lines in a hydrogen-rich atmosphere at 500 °C for 1 h. The LWR (i.e., 3 σLWR) of these nickel nanolines was found to be 2.9 nm. The technique is general and is likely to be suitable for fabrication of nanostructures of most commonly used metals (and their alloys), such as iron, cobalt, nickel, copper, tungsten, molybdenum, and so on, from their respective metal–organic compounds.
    Advanced Functional Materials 06/2010; 20(14):2317 - 2323. · 10.44 Impact Factor
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    ABSTRACT: In quantum computation, information is processed by gates that must coherently couple separate qubits. In many systems the qubits are naturally coupled, but such an always-on interaction limits the algorithms that may be implemented. Coupling interactions may also be directed in devices and circuits that are provided with additional control wiring. This can be achieved by adjusting the gate voltage in a semiconductor device or an additional flux in a superconducting device. Such control signals must be applied adiabatically (limiting the speed) and the additional wiring provides pathways for noise, which leads to decoherence. Here we demonstrate an alternative approach to coupling by exploiting the nonlinear behaviour of a degenerately doped silicon transistor. A single transistor can exhibit a large number of individual resonances, which are seen as changes in the source-drain current of a dc-biased device. These resonances may be addressed in frequency space due to their high quality factors. Two widely separated resonances are addressed and coupled in three-frequency spectroscopy by ensuring that the third frequency corresponds to the difference between the two individual resonances. The nonlinearity causes the generation of additional driving signals with appropriate frequency and phase relationships to ensure coupling, resulting in additional spectroscopic features that could be exploited for rapid state manipulation and gate operations. Comment: 6 pages, 3 figures
    Applied Physics Letters 03/2010; · 3.52 Impact Factor
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    A. Rossi, D. G. Hasko
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    ABSTRACT: Resonant microwave-assisted and DC transport are investigated in degenerately doped silicon single electron transistors. A model based on hopping via localized impurity states is developed and first used to explain both the DC temperature dependence and the AC response. In particular, the non-monotonic power dependence of the resonant current under irradiation is proved to be consistent with spatial Rabi oscillations between these localized states. Comment: 9 pages, 5 figures
    Journal of Applied Physics 03/2010; · 2.21 Impact Factor
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    ABSTRACT: In this paper, we demonstrate a double nanoimprinting process that allows the formation of nanostructured polymer heterojunctions of composition and morphology that can be selected independently. We fabricated photovoltaic (PV) devices with extremely high densities (10(14)/mm(2)) of interpenetrating nanoscale columnar features in the active polymer blend layer. The smallest feature sizes are as small as 25 nm on a 50 nm pitch, which results in a spacing of heterojunctions at or below the exciton diffusion length. Photovoltaic devices based on double-imprinted poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (F8TBT)/ poly(3-hexylthiophene) (P3HT) films are among the best polymer-polymer blend devices reported to date with a power conversion efficiency (PCE, eta(e)) of 1.9%.
    Nano Letters 03/2010; 10(4):1302-7. · 13.03 Impact Factor
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    ABSTRACT: Coherent coupling between a large number of qubits is the goal for scalable approaches to solid state quantum information processing. Prototype systems can be characterized by spectroscopic techniques. Here, we use pulsed-continuous wave microwave spectroscopy to study the behavior of electrons trapped at defects within the gate dielectric of a sol-gel-based high-k silicon MOSFET. Disorder leads to a wide distribution in trap properties, allowing more than 1000 traps to be individually addressed in a single transistor within the accessible frequency domain. Their dynamical behavior is explored by pulsing the microwave excitation over a range of times comparable to the phase coherence time and the lifetime of the electron in the trap. Trap occupancy is limited to a single electron, which can be manipulated by resonant microwave excitation and the resulting change in trap occupancy is detected by the change in the channel current of the transistor. The trap behavior is described by a classical damped driven simple harmonic oscillator model, with the phase coherence, lifetime and coupling strength parameters derived from a continuous wave (CW) measurement only. For pulse times shorter than the phase coherence time, the energy exchange between traps, due to the coupling, strongly modulates the observed drain current change. This effect could be exploited for 2-qubit gate operation. The very large number of resonances observed in this system would allow a complex multi-qubit quantum mechanical circuit to be realized by this mechanism using only a single transistor.
    02/2010;
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    ABSTRACT: An ultra-small Coulomb blockade device can be regarded as a mesoscopic artificial atom system and provides a rich experimental environment for studying quantum transport phenomena[1]. Previously, these quantum effects have been investigated using relatively large devices at ultra-low temperatures, where they give rise to a fine additional structure on the Coulomb oscillations [2-13]. Here, we report transport measurements carried out on a sub-2nm single-electron device; this size is sufficiently small that Coulomb blockade, and other quantum effects, persist up to room temperature (RT). These devices were made by scaling the size of a FinFET structure down to an ultimate limiting form, resulting in the reliable formation of a sub-2nm silicon Coulomb island. Four clear Coulomb diamonds can be observed at RT and the 2nd Coulomb diamond is unusually large, due to quantum confinement. The observed characteristics are successfully modeled on the basis of a very low electron number on the island, combined with Pauli spin exclusion. These effects offer additional functionality for future RT-operating single-electron device applications Comment: 7 pages, 4 figures
    01/2010;
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    ABSTRACT: The aim of this paper is to review our recent results on the growth and optimization of carbon nanotubes (CNTs) and CNT/Zinc Oxide nanostructures and present and discuss their suitability for various applications such as cold cathode electron sources for use in x-ray sources and lighting.
    01/2010;
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    ABSTRACT: Conventional patterning of HfO(2) as a gate dielectric is a multistep complicated process that involves deposition of oxide, photolithography, and hard mask etching. In order to simplify the process of HfO(2) patterning, the authors have developed photo- and electron beam-sensitive spin-coatable HfO(2) resists for direct writing. They were prepared by reacting hafnium tert-butoxide with benzoylacetone in n-butanol and were found to be highly stable in air. Fourier transform infrared studies suggest that exposure to radiation results in the gradual removal of organic material from the resist and the enrichment of the resist with inorganics. This makes the exposed resist insoluble in organic solvents such as ethanol, thereby providing high-resolution negative patterns as small as similar to 10 nm wide. A silicon-on-insulator field effect transistor has been fabricated using sol-gel-derived HfO(2) resist as a high-k gate dielectric and characterized over a range of temperatures. At room temperature a relatively high gate leakage current was observed which degrades the device performance, but at low temperatures this leakage current is strongly suppressed.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2010; 28(1):90. · 1.36 Impact Factor
  • Advanced Functional Materials 01/2010; 20(14). · 10.44 Impact Factor
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    ABSTRACT: Silicon single-electron transistors are promising nanodevices for implementation of quantum logic gates. Single frequency continuous wave microwave spectroscopy, carried out under cryogenic conditions on dc biased degenerately doped transistors have previously shown many high quality factor resonances in the drain current modulation, indicating the presence of long-lived excitations. However, such measurements are unable to indicate coupled behaviour between the systems undergoing resonance. Coupled behaviour is a necessary precursor for quantum gate operation. In this work, we investigate the response of devices to two frequency continuous wave microwave spectroscopy, which is a potential method for induced coupling.
    Journal of Physics Conference Series 11/2009; 193(1):012048.

Publication Stats

3k Citations
452.92 Total Impact Points

Institutions

  • 1984–2013
    • University of Cambridge
      • • Department of Engineering
      • • Department of Physics: Cavendish Laboratory
      • • Centre for Research in Microeconomics
      • • Department of Materials Science and Metallurgy
      Cambridge, England, United Kingdom
  • 2011
    • Chungbuk National University
      • Department of Physics
      Chinsen, North Chungcheong, South Korea
  • 2008
    • Samsung Advanced Institute of Technology
      Usan-ri, Gyeonggi Province, South Korea
  • 2004
    • Claude Bernard University Lyon 1
      Villeurbanne, Rhône-Alpes, France
  • 2003
    • Hanyang University
      Sŏul, Seoul, South Korea