1,721,441 research outputs found
Light Emitting diodes based on anodically oxidized silicon/porous silicon heterojunction
No full textAn improved test device, based on the light emitting device (LED) presented in the following article (L. Pavesi, R. Guardini, P. Bellutti, Thin Solid Films 297 (1997) 272) is reported. The whole processing of the diode is CMOS compatible and the porous Si (PS) formation is at the end of the run. The idea of the LED is to exploit the doping selectivity of the silicon anodization by forming n+ -type doped crystalline Si stripes floating over the porous silicon layer. Electrical injectionis through the n+ stripes into the PS, i.e. through a SI/PS heterojunction. Here, the electrical and optical properties of the electochemically oxidized LED are characterized. Anodic oxidation improves the LED performance both in terms of stability (more than 8 days under CW excitation) and efficiency (a factor 3 or higher with respect to the as-grown LED
Electrochemically oxidised porous silicon microcavities
No full textAgeing effects in porous silicon microcavities result in emission enhancement and resonance peak blueshift. In this paper we propose electrochemical oxidation as a method to control these effects. Properties of porous silicon microcavities obtained after anodic oxidation are compared to those of microcavities aged in air for several months. This evidences that emission enhancement and resonance peak shift are two different phenomena and the effects of anodic and naturally oxidation are not the same. A significant suppression of peak shift due to ageing is achieved, and the extent of this stabilisation increases with the oxidation time, but for long oxidation times the microcavity properties are degraded
All porous silicon microcavities: growth and physics
No full textThe spontaneous emission of a material can be controlled by placing it in a micron-sized optical cavity. In this paper we introduce the subject and we discuss the realization, the physics and perspective applications of all porous silicon microcavities. The emission properties of the cavities have been characterized as a function of the temperature, of the excitation power and of the response time. Coupled microcavities are demonstrated. Modeling of the structure have been performed on the basis of a transfer matrix approximation
Nanosilicon photonics
No full textSilicon photonics is no longer an emerging field of research and technology but a present reality with commercial products available on the market, where low-dimensional silicon (nanosilicon or nano-Si) can play a fundamental role. After a brief history of the field, the optical properties of silicon reduced to nanometric dimensions are introduced. The use of nano-Si, in the form of Si nanocrystals, in the main building blocks of silicon photonics (waveguides. modulators, sources and detectors) is reviewed and discussed. Recent advances of nano-Si devices such as waveguides, optical resonators (linear, rings, and disks) are treated. Emphasis is placed on the visible optical gain properties of nano-Si and to the sensitization effect on Er ions to achieve infrared light amplification. The possibility of electrical injection in light-emitting diodes is presented as well as the recent attempts to exploit nano-Si for solar cells. In addition, nonlinear optical effects that will enable fast all-optical switches are described. [GRAPHICS] (C) 2009 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Silicon nanocrystals enabling silicon Photonics
No full textSilicon Photonics is an emerging field of research and technology, where nano-silicon can play a fundamental role. In this chapter, the main building blocks of Silicon Photonics ( waveguides, modulators, sources and detectors) are reviewed and compared to their counterparts made by Si nanocrystals. In addition, non-linear optical effects in Si nanocrystals which will enable fast all-optical switches are presented as well as our recent research efforts to obtain optical amplification at 1550 nm by using Er ions and the sensitizing properties of Si nanocrystals
Low dimensional Silicon as a photonics material
No full textIn this chapter the state-of-the-art on the development of low dimensional silicon for application in photonics is presented with the aim to settle the status and try to weight out the perspectives. The necessity for Si-based photonics is introduced, and special emphasis is dedicated to the subject which is at the forefront of the today discus-sion: the route to a silicon light source. Two examples are detailed: silicon nanocrystals and Er doped silicon nanocrystals
Evidence of the Exciton-Plasma Transition in the Emission Spectra of GaSe
No full textWe present luminescence spectra of gallium selenide at 2 K in which a slow and continuous evolution from excitonic recombination to an electron-hole plasma emission is observed when the excitation intensity is increased. We find a small red-shift and a broadening of the direct exciton emission line which is followed by its disappearing. We explain these results with a model which takes into account the electron-hole correlation
Patterns of genetic structuring and levels of differentiation in supralittoral talitrid amphipods: an overview
No full textTalitrids are the only family within the order Amphipoda to have colonised supralittoral and terrestrial environments. They live in a variety of settings, from sandy to rocky and pebble beaches, to river and lake banks, and to leaf litter and caves. A common feature is the absence of a planktonic larval stage to facilitate passive dispersal over long-distances. However, some species have broad distributions. Genetic studies over the past 25 years have tried to explain this apparent contradiction by assessing patterns of species genetic structuring on different geographical scales. Here, we review the molecular studies available to date and focus on the population genetics of talitrids. Most of these studies considered populations in the Mediterranean area, but also along the Atlantic coast and in Canary Island caves. From this review, the group emerges as a potential model to understand processes of dispersal and divergence in non-highly-vagile supralittoral organisms. At the same time, studies on these issues are still too restricted geographically: a worldwide scale including different regions would provide us with a better perspective on these problems
Porous silicon microcavities as optical chemical sensors
No full textThe optical properties of porous silicon microcavities are strongly dependent on the environment. For highly luminescent samples, both the luminescence intensity and the peak position are affected by organic substances, giving the possibility to obtain dual-parameter optical sensors. While the peak position depends on the organic compound refractive index, luminescence intensity depends on its low-frequency dielectric constant. This allows the discrimination between different organic substances. This sensor is particularly interesting for solvents with low dielectric constant, where the response of electrical sensors is very weak
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