D. G. Hasko

University of Cambridge, Cambridge, England, United Kingdom

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Publications (232)509.35 Total impact

  • X. Bian · W. I. Milne · D. G. Hasko
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    ABSTRACT: We investigate the high-frequency operation of a percolation field effect transistor to monitor microwave excited single trapped charge. Readout is accomplished by measuring the effect of the polarization field associated with the oscillating charge on the AC signal generated in the channel due to charge pumping. This approach is sensitive to the relative phase between the polarization field and the pumped current, which is different from the conventional approach relying on the amplitude only. Therefore, despite the very small influence of the single oscillating trapped electron, a large signal can be detected. Experimental results show large improvement in both signal-to-noise ratio and measurement bandwidth.
    No preview · Article · Jul 2015 · Applied Physics Letters
  • J. J. Lee · J. S. Kim · S. J. Shin · J. B. Choi · D. G. Hasko
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    ABSTRACT: We have implemented a Si-based coupled double-dot device with five independent gates vertically layered above the active channel, which can provide more effective controllability of interdot coupling without changing the potential shape of an individual dot. We observed a transition from a merged single dot to the coupled double dot by adjusting the interdot coupling strength via a central gate. From the honeycomb charge stability diagram, the capacitance-related critical parameters of the coupled double dot, which will be of impotance in the Si-based two-qubit gate applications, are deduced.
    No preview · Article · Jun 2014 · Journal- Korean Physical Society
  • 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.
    No preview · Article · Aug 2013 · Applied Physics Letters
  • J. O. Tenorio-Pearl · W. I. Milne · D. G. Hasko
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    ABSTRACT: The behavior of trapped electrons, in a dielectric close to the channel of a silicon SOI-FET, is studied by cryogenic microwave spectroscopy. On-resonance microwave excitation causes one of these trapped electrons to undergo spatial Rabi oscillations between widely separated trap sites. This charge displacement causes a change in the drain current of the transistor, resulting in high quality factor resonances in continuous wave spectroscopy. The potential of this effect for non-classical information processing is investigated through polychromatic single-shot spectroscopy, using on-resonance and difference frequencies. Interaction between different trapped electrons is seen in the post excitation behavior and the possibilities of quantum gate operations are discussed.
    No preview · Article · Jun 2013 · ECS Transactions
  • S. Fleming · W. I. Milne · D. G. Hasko
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    ABSTRACT: Electrical detection of solid-state charge qubits requires ultrasensitive charge measurement, typically using a quantum point contact or single-electron-transistor, which imposes strict limits on operating temperature, voltage and current. A conventional FET offers relaxed operating conditions, but the back-action of the channel charge is a problem for such small quantum systems. Here, we discuss the use of a percolation transistor as a measurement device, with regard to charge sensing and backaction. The transistor is based on a 10nm thick SOI channel layer and is designed to measure the displacement of trapped charges in a nearby dielectric. At cryogenic temperatures, the trapped charges result in strong disorder in the channel layer, so that current is constrained to a percolation pathway in sub-threshold conditions. A microwave driven spatial Rabi oscillation of the trapped charge causes a change in the percolation pathway, which results in a measurable change in channel current.
    No preview · Article · Jun 2013 · ECS Transactions
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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.
    No preview · Article · Apr 2013 · Applied Physics Letters
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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.
    No preview · Article · Oct 2012 · Applied Physics Letters
  • J. O. Tenorio-Pearl · W. I. Milne · D. G. Hasko
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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.
    No preview · Article · Jul 2012 · Journal of Applied Physics
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    ABSTRACT: Wireless power transfer is experimentally demonstrated by transmission between an AC power transmitter and receiver, both realised using thin film technology. The transmitter and receiver thin film coils are chosen to be identical in order to promote resonant coupling. Planar spiral coils are used because of the ease of fabrication and to reduce the metal layer thickness. The energy transfer efficiency as a function of transfer distance is analysed along with a comparison between the theoretical and the experimental results.
    No preview · Article · Jan 2012 · MRS Online Proceeding Library
  • Xueni Zhu · David G. Hasko · Stephan Hofmann · William I. Milne
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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.
    No preview · Article · Jun 2011 · Journal of Applied Physics
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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.
    Preview · Article · Mar 2011 · Nano Letters
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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.
    No preview · Article · Jan 2011 · Advanced Functional Materials
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    ABSTRACT: A new method is presented, based on the discrete Fourier Transform, for the design of aperiodic lattices to be used in photonic bandgap engineering. Designing an aperiodic lattice by randomly choosing defects is unlikely to result in useful optical transmission characteristics. By contrast, this new method allows an aperiodic lattice to be designed directly from the desired optical characteristic. The use of this method is illustrated with a design for a structure to realise two transmission wavelengths in the stopband of a one-dimensional photonic lattice. This design has been fabricated in silicon-on-insulator and some optical characteristics are given.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The formation of silicon-on-insulator structures, by recrystallising polycrystalline silicon films with a dual electron beam technique, has been studied over a wide range of conditions. The quality of the layers has been assessed by examining cross-sections in the SEM and optical microscopy of the surface after a Secco etch. The range of line powers which gives device-worthy single crystal material becomes greater as the sweep speed increases and as the background temperature is reduced. The extent of melting into the substrate in the seed windows and below the isolating oxide was determined from the movement of an arsenic implant. The experimental results are compared to the predictions from a one dimensional model for the heat flow.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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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.
    Preview · Article · Jan 2011 · MRS Online Proceeding Library
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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.
    No preview · Article · Sep 2010 · Applied Physics Letters
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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.
    Preview · Article · Sep 2010 · Applied Physics Letters

Publication Stats

5k Citations
509.35 Total Impact Points

Institutions

  • 1984-2015
    • University of Cambridge
      • • Department of Engineering
      • • Department of Physics: Cavendish Laboratory
      • • Nanoscience Centre
      • • Centre for Research in Microeconomics
      • • Department of Materials Science and Metallurgy
      Cambridge, England, United Kingdom
  • 1991
    • University of Western Australia
      Perth City, Western Australia, Australia