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Le Touquet – Paris-Plage, France

Sun G.C.,GESEC R and D Inc. | Rao R.,GESEC R and D Inc. | Makham S.,GESEC R and D Inc. | Bourgoin J.C.,GESEC R and D Inc. | And 11 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

To be used for X-ray imaging, semiconductor materials must exhibit good and uniform electronic properties. Epitaxial layers are therefore better adapted than bulk materials which contain dislocations, precipitates and point defects in variable concentrations depending on the growth mode and the nature of the material. However, they have to be thick enough to absorb photons efficiently. We produced thick epitaxial layers using a proprietary technique and made p/i/n (200300 μm thick) diodes with this new material. These diodes are characterized by a large reverse current, which can originate from electron emission from deep level defects present in the depleted region or be a leakage current. In order to answer this question, we performed a characterization of the defects present in the material. Here, we describe results obtained from X-ray diffraction, X-ray topography, time resolved photoluminescence and resistivity measurements. We also investigated the possible effect of hydrogen. From these observations, we deduced that defects exhibiting an electrical role are in negligible concentration and concluded that the high reverse current observed is a leakage current. © 2010 Elsevier B.V. All rights reserved.

Evans D.A.,Aberystwyth University | Vearey-Roberts A.R.,Aberystwyth University | Roberts O.R.,Aberystwyth University | Roberts O.R.,Element Six | And 7 more authors.
Journal of Applied Physics | Year: 2013

The transport and optical band gaps for the organic semiconductor tin (II) phthalocyanine (SnPc) and the complete energy band profiles have been determined for organic-inorganic interfaces between SnPc and III-V semiconductors. High throughput measurement of interface energetics over timescales comparable to the growth rates was enabled using in situ and real-time photoelectron spectroscopy combined with Organic Molecular Beam Deposition. Energy band alignment at SnPc interfaces with GaAs, GaP, and InP yields interface dipoles varying from -0.08 (GaP) to -0.83 eV (GaAs). Optical and transport gaps for SnPc and CuPc were determined from photoelectron spectroscopy and from optical absorption using spectroscopic ellipsometry to complete the energy band profiles. For SnPc, the difference in energy between the optical and transport gaps indicates an exciton binding energy of (0.6 ± 0.3) eV. © 2013 AIP Publishing LLC.

Simonsen I.,Norwegian University of Science and Technology | Simonsen I.,Institute Des Nanosciences Of Paris | Kryvi J.B.,Norwegian University of Science and Technology | Maradudin A.A.,University of California at Irvine | Leskova T.A.,University of California at Irvine
Computer Physics Communications | Year: 2011

An approach is introduced for performing rigorous numerical simulations of electromagnetic wave scattering from randomly rough, perfectly conducting surfaces. It is based on a surface integral technique, and consists of determining the unknown electric surface current densities from which the electromagnetic field everywhere can be determined. The method is used to study the scattering of a p-polarized beam from an anisotropic Gaussian, randomly rough, perfectly conducting surface. It is demonstrated that the surface anisotropy gives rise to interesting and pronounced signatures in the angular intensity distribution of the scattered light. The origins of these features are discussed. © 2011 Elsevier B.V. All rights reserved.

Zallo E.,Leibniz Institute for Solid State and Materials Research | Atkinson P.,Leibniz Institute for Solid State and Materials Research | Atkinson P.,Institute Des Nanosciences Of Paris | Rastelli A.,Leibniz Institute for Solid State and Materials Research | Schmidt O.G.,Leibniz Institute for Solid State and Materials Research
Journal of Crystal Growth | Year: 2012

Modifying the shape of nanoholes formed by arsenic debt epitaxy by the overgrowth of a thin GaAs buffer is shown to provide a simple and robust method to grow low density lateral In(Ga)As quantum dot pairs (QDPs). We present here a systematic study of the effect of GaAs buffer thickness, InAs deposition amount, substrate temperature and arsenic overpressure on dot nucleation and QDP formation. A (1030) nm GaAs buffer over nanoholes initially ∼10.5nm deep, (6080) nm wide results in up to 80% of the nanoholes containing QDPs. The QD pairs are aligned along the [110] direction and have centre-to-centre separation of ∼38nm. These QDPs form following InAs deposition between 1.3 ML and 1.6 ML at 490 °C under an arsenic arrival flux of 0.6 ML/s. From the infilling of the hole prior to QD formation, we estimate a net indium surface flux towards the hole of ∼7 times the incident flux. The substrate temperature does not significantly alter the dot distribution over the range (470510) °C. However, the QDP formation is very sensitive to the arsenic overpressure over the range (0.61.2) ML/s because of a partial collapse of the nanohole, due to mass transport as the substrate passes through the (2×4) to c(4×4) surface reconstruction around 500 °C. © 2011 Elsevier B.V. All rights reserved.

Gualtieri A.F.,University of Modena and Reggio Emilia | Canovi L.,University of Modena and Reggio Emilia | Viani A.,University of Modena and Reggio Emilia | Bertocchi P.,Ferrari | And 5 more authors.
Journal of the European Ceramic Society | Year: 2013

This work elucidates the mechanism responsible for the lustre effect of scheelite-based glazes for single-firing wall tiles. The surface decoration is obtained with a thin film composed of a Si-Ca-Zn-Al-K-B frit and 10wt% WO3 on zircon-engobed substrates for single-firing wall tiles (maximum temperature of 1130°C for 50min). The observed lustre effect is sub-adamantine and pearlescent. It is sub-adamantine because scheelite nanocrystals at the surface, with a relatively high refractive index (n=1.93), cause considerable reflection of light. The lustre is also weakly pearlescent because the nano-crystals oriented with the (004) plane parallel to the surface give interference with the underlying glassy layer (n≈1.5), where randomly dispersed scheelite crystals occur. This model apparently applies to the glazes decorated with ceria, although the latter exhibits iridescence due to the high refractive index of ceria (n=2.05) which yields stronger interference effect with the underlying glassy substrate. © 2013 Elsevier Ltd.

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