Priolo F.,University of Catania |
Priolo F.,CNR Institute for Microelectronics and Microsystems |
Gregorkiewicz T.,University of Amsterdam |
Galli M.,University of Pavia |
Krauss T.F.,University of York
Nature Nanotechnology | Year: 2014
Silicon has long been established as the material of choice for the microelectronics industry. This is not yet true in photonics, where the limited degrees of freedom in material design combined with the indirect bandgap are a major constraint. Recent developments, especially those enabled by nanoscale engineering of the electronic and photonic properties, are starting to change the picture, and some silicon nanostructures now approach or even exceed the performance of equivalent direct-bandgap materials. Focusing on two application areas, namely communications and photovoltaics, we review recent progress in silicon nanocrystals, nanowires and photonic crystals as key examples of functional nanostructures. We assess the state of the art in each field and highlight the challenges that need to be overcome to make silicon a truly high-performing photonic material. © 2014 Macmillan Publishers Limited.
Camarda M.,CNR Institute for Microelectronics and Microsystems
Surface Science | Year: 2012
In this article we use three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on misoriented hexagonal (4H and 6H) substrates. We analyze the quality of the 3C-SiC film varying the polytype, the miscut angle and the initial surface morphology of the substrate. We find that the use of 6H misoriented (4°-10°off) substrates, with step bunched surfaces, can strongly improve the quality of the cubic epitaxial film whereas the 3C/4H growth is affected by the generation of dislocations, due to the incommensurable periodicity of the 3C (3) and the 4H (4) polytypes. For these reasons, a proper pre-growth treatment of 6H misoriented substrates can be the key for the growth of high quality, twin free, 3C-SiC films. © 2012 Elsevier B.V. All rights reserved.
Debernardi A.,CNR Institute for Microelectronics and Microsystems
Physical Review B - Condensed Matter and Materials Physics | Year: 2012
I present an ab initio study of the phase stability and dielectric constant (κ 0) of Hf 1-xGe xO 2 alloy as a function of Ge concentration in the range 0≤x≤0.25. I determine the critical concentration x c at which the monoclinic structure (the stable phase at low x and at low temperatures) has a phase transition into the high-κ 0 fluorite structure. I found that, at x c, the fluorite phase presents a dielectric constant that is more than 50% higher than the orientationally averaged dielectric constant of undoped bulk monoclinic phase. I studied the effect of temperature on this phase transition. I identified the microscopic mechanisms which influence the dielectric properties of the fluorite phase finding that the decrease of the Born effective charge of Ge with respect to that of Hf is locally compensated by a variation of the Born effective charge of the O atoms which are neighbors of the Ge. I predict that the bulk modulus of this superhard oxide increases as a function of doping. My results are relevant to improve, by Ge alloying, the dielectric and mechanical properties of hafnia in advanced technological applications. © 2012 American Physical Society.
Prokopidis K.P.,Aristotle University of Thessaloniki |
Zografopoulos D.C.,CNR Institute for Microelectronics and Microsystems
Journal of Lightwave Technology | Year: 2013
A generalized auxiliary differential equation (ADE) finite-difference time-domain (FDTD) dispersive scheme is introduced for the rigorous simulation of wave propagation in metallic structures at optical frequencies, where material dispersion is described via an arbitrary number of Drude and critical point terms. The implementation of an efficient perfectly matched layer for the termination of such media is also discussed and demonstrated. The model's validity is directly compared with both analytical and numerical results that employ known dispersion schemes, for the case of two benchmark examples, transmission through a thin metal film and scattering from a metallic nanocylinder. Furthermore, the accuracy of the proposed method is also demonstrated in the study of the optical properties of Ag and Au metal-insulator-metal waveguides, filters, and resonators, which also involve dielectrics whose material dispersion is described by the Sellmeier model. © 2013 IEEE.
Zografopoulos D.C.,CNR Institute for Microelectronics and Microsystems |
Beccherelli R.,CNR Institute for Microelectronics and Microsystems
Plasmonics | Year: 2013
A long-range surface plasmon polariton variable optical attenuator based on available nematic liquid crystals and polymers is proposed and theoretically investigated. It is demonstrated that the electro-optic control of the nematic molecular orientation is capable of tuning the level of index asymmetry of an Au stripe waveguide and the key properties of the fundamental long-range plasmonic mode, such as modal profile and propagation losses. By proper structural design and material selection, plasmonic in-line intensity modulators are designed, which exhibit very low power consumption, extinction ratios in excess of 30 dB, and insertion losses as low as 1 dB for a device length in the millimeter range. Such active plasmonic elements are envisaged to be used in interchip photonics bus interconnects. © 2012 Springer Science+Business Media, LLC.