Science

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Now showing 1 - 10 of 156
  • (1998) Corkish, Richard; Sproul, Alistair; Puzzer, Tom; Altermatt, Peter; Heiser, Gernot; Luke, Keung
    Conference Paper

  • (1998) Bradley, Peter; Rozenfeld, Anatoly; Lee, Kevin; Jamieson, Dana; Heiser, Gernot; Satoh, S
    Journal Article
    The first results obtained using a SOI device for microdosimetry applications are presented. Microbeam and broadbeam spectroscopy methods are used for determining minority carrier lifetime and radiation damage constants. A spectroscopy model is presented which includes the majority of effects that impact spectral resolution. Charge collection statistics were found to substantially affect spectral resolution. Lateral diffusion effects significantly complicate charge collection

  • (1997) Corkish, Richard; Puzzer, Tom; Sproul, Alistair; Luke, Keung; Heiser, Gernot
    Conference Paper

  • (1996) Sproul, Alistair; Edminston, Sean; Puzzer, Tom; Heiser, Gernot; Wenham, Stuart; Green, Martin; Young, Timothy
    Conference Paper
    An analytical model is developed to decribe recombination currents arising from recombination at grain boundaries (GBs) in the depletion region of a p-n junction solar cell. Grain boundaries are modelled as having a single energy evel in the energy gap, and partial occupancy of these stats gives raise to a chage on the GB. The analytical model is compared to a complete numerical simulation package (DESSIS) and found to be in excellent agreement. Additionally,. cross sectional EBIC images of a multilayer device containing vertical GBs are presented. The experimental data is comared qualitatively with results derived from numerical modelling.

  • (1996) Altermatt, Peter; Heiser, Gernot; Dai, Ximing; Jurgens, J; Aberle, Armin; Robinson, Steven J.; Young, Timothy; Wenham, Stuart; Green, Martin
    Journal Article
    The passivated emitter, rear locally diffused (PERL) cells, fabricated in our laboratory, reach an efficiency of 24.0%, the highest value for any silicon-based solar cell under terrestrial illumination. In an attempt to improve the rear surface passivation, which is usually obtained by a thermally grown oxide, we add a floating (i.e., noncontacted) p-n junction at the rear surface, resulting in the passivated emitter, rear floating p-n junction (PERF) cell design. Although these cells exhibit record 1-sun open-circuit voltages of up to 720 mV, their efficiency is degraded by nonlinearities ("shoulders") in the logarithmic I-V curves. In order to understand and manipulate such nonlinearities, this paper presents a detailed investigation of the internal operation of PERF cells by means of numerical modelling based on experimentally determined device parameters. From the model, we derive design rules for optimum cell performance and develop a generalized argumentation that is suitable to compare the passivation properties of different surface structures. For example, the oxidized rear surface of the PERL cell is treated as an electrostatically induced floating junction in this approach and analogies to the diffused floating p-n junction are drawn. Our simulations indicate that optimum rear surface passivation can be obtained in three different ways. (i) The floating junction of the PERF cell should be very lightly doped, resulting in a sheet resistivity of 5000 Omega/[D'Alembertian], and losses due to shunt leaking paths between the p-n junction and the rear metal contacts must be avoided. (ii) The rear surface of the PERL cell should be passivated by chemical vapor deposition of a silicon nitride film containing a larger positive interface charge density than exists in thermally grown oxides. (iii) An external gate can be added at the rear with low leakage currents and gate voltages of around 15 V.


  • (1997) Wolfe, Joseph; Yoon, Yong; Pope, J
    Journal Article
    Quantitative nuclear magnetic resonance was used to measure the freezing behaviour of lamellar phases of phosphatidylcholine in water and in solutions of sorbitol. Both solute and solvent were deuterated in different series of experiments to allow the calculation of the partitioning of solute and solvent molecules between the lamellar phase and unfrozen bulk solution. Sorbitol, as well as water, was found to redistribute between these phases as a function of temperature. The results show a strong, repulsive, interlamellar force which decreases approximately exponentially with hydration. Compared to measurements on lipid/water systems and solute/water systems, the hydration of the lamellar phase containing solutes is slightly less than the sum of the hydrations of lipid and solute at any given chemical potential of water. For a lamellar phase with a given quantity of lipid, interlamellar sorbitol and water, reduction of chemical potential of water is greater than that due to lipid acting alone plus that due to solute acting alone.

  • (1997) Smith, John; Epps, Julien; Wolfe, Joseph
    Journal Article
    Acoustic resonances of the vocal tract give rise to formants (broad bands of acoustic power) in the speech signal when the vocal tract is excited by a periodic signal from the vocal folds. This paper reports a novel instrument which uses a real-time, non-invasive technique to measure these resonances accurately during phonation. A broadband acoustic current source is located just outside the mouth of the subject and the resulting acoustic pressure is measured near the lips. The contribution of the speech signal in the pressure spectrum is then digitally suppressed and the resonances are calculated from the input impedance of the vocal tract as a function of frequency. The external excitation signal has a much smaller harmonic spacing than the periodic signal from the vocal folds and consequently the resonances are determined much more accurately due to the closer sampling. This is particularly important for higher pitched voices and we demonstrate that this technique can be markedly superior to the curve-fitting technique of linear prediction. The superior frequency resolution of this instrument which results from external vocal tract excitation can provide the precise, stable, effective, articulatory feedback considered essential for some language-learning and speech therapy applications.

  • (1999) Bandyopadhyay, Srikanta; Gowripalan, Nadarajah; Rizkalla, S; Dutta, P; Bhattacharyya, D
    Conference Paper

  • (2000) Kaog, G J P; Gowripalan, Nadarajah; Bandyopadhyay, Srikanta
    Conference Paper