In the last 30 days

• Open/close Solid-state lighting: an energy-economics perspective

  J Y Tsao et al 2010 J. Phys. D: Appl. Phys. 43 354001 Tag this article

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  Artificial light has long been a significant factor contributing to the quality and productivity of human life. As a consequence, we are willing to use huge amounts of energy to produce it. Solid-state lighting (SSL) is an emerging technology that promises performance features and efficiencies well beyond those of traditional artificial lighting, accompanied by potentially massive shifts in (a) the consumption of light, (b) the human productivity and energy use associated with that consumption and (c) the semiconductor chip area inventory and turnover required to support that consumption. In this paper, we provide estimates of the baseline magnitudes of these shifts using simple extrapolations of past behaviour into the future. For past behaviour, we use recent studies of historical and contemporary consumption patterns analysed within a simple energy-economics framework (a Cobb–Douglas production function and profit maximization). For extrapolations into the future, we use recent reviews of believed-achievable long-term performance targets for SSL. We also discuss ways in which the actual magnitudes could differ from the baseline magnitudes of these shifts. These include: changes in human societal demand for light; possible demand for features beyond lumens; and guidelines and regulations aimed at economizing on consumption of light and associated energy.

• Open/close Studies of tunnel MOS diodes I. Interface effects in silicon Schottky diodes

  H C Card and E H Rhoderick 1971 J. Phys. D: Appl. Phys. 4 1589 Tag this article

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  A theoretical and experimental study has been made of silicon Schottky diodes in which the metal and semiconductor are separated by a thin interfacial film. A generalized approach is taken towards the interface states which considers their communication with both the metal and the semiconductor. Diodes were fabricated with interfacial films ranging from 8 to 26 Å in thickness, and their characteristics are related to this model. The effects of reduced transmission coefficients together with fixed charge in the film are investigated. The interpretation of the current-voltage characteristics and the validity of the C ⁻²- V method in the determination of diffusion potentials are discussed.

• Open/close Recent progress in nanoimprint technology and its applications

  L Jay Guo 2004 J. Phys. D: Appl. Phys. 37 R123 Tag this article

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  Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional techniques. This article reviews the basic principles of nanoimprint technology and some of the recent progress in this field. It also explores a few alternative approaches that are related to nanoimprint as well as additive approaches for patterning polymer structures. Nanoimprint technology can not only create resist patterns as in lithography but can also imprint functional device structures in polymers. This property is exploited in several non-traditional microelectronic applications in the areas of photonics and biotechnology.

• Open/close White light emitting diodes with super-high luminous efficacy

  Yukio Narukawa et al 2010 J. Phys. D: Appl. Phys. 43 354002 Tag this article

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  We fabricated three types of high luminous efficacy white light emitting diodes (LEDs). The first was a white LED with a high luminous efficacy (η _L) of 249 lm W ⁻¹ and a high luminous flux ( _v) of 14.4 lm at a forward-bias current of 20 mA. This η _L was approximately triple that of a tri-phosphor fluorescent lamp (90 lm W ⁻¹). The blue LED used as the excitation source in this white LED had a high output power ( _e) of 47.1 mW and a high external quantum efficiency (η _ex) of 84.3%. The second was a high-power white LED, fabricated from the above high-power blue LED, and had a high _e of 756 mW at 350 mA. _v and η _L of the high-power white LED were 203 lm and 183 lm W ⁻¹ at 350 mA, respectively. The third was a high-power white LED fabricated from four high-power blue LED dies. _v and η _L of the high-power white LED were 1913 lm and 135 lm W ⁻¹ at 1 A, respectively. The white LED had a higher flux than a 20 W-class fluorescent lamp and 1.5 times the luminous efficacy of a tri-phosphor fluorescent lamp (90 lm W ⁻¹).

• Open/close LED light sources (light for the future)

  N Grandjean 2010 J. Phys. D: Appl. Phys. 43 350301 Tag this article

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  Generating white light from electricity with maximum efficacy has been a long quest since the first incandescent lamp was invented by Edison at the end of the 19th century. Nowadays, semiconductors are making reality the holy grail of converting electrons into photons with 100% efficiency and with colours that can be mixed for white light illumination. The revolution in solid-state lighting (SSL) dates to 1994 when Nakamura reported the first high-brightness blue LED based on GaN semiconductors. Then, white light was produced by simply combining a blue dye with a yellow phosphor. After more than a decade of intensive research the performance of white LEDs is quite impressive, beating by far the luminous efficacy of compact fluorescent lamps. We are likely close to replacing our current lighting devices by SSL lamps. However, there are still technological and fabrication cost issues that could delay large market penetration of white LEDs. Interestingly, SSL may create novel ways of using light that could potentially limit electricity saving. Whatever the impact of SSL, it will be significant on our daily life.

  The purpose of this special cluster issue is to produce a snapshot of the current situation of SSL from different viewing angles. In an introductory paper, Tsao and co-workers from Sandia National Laboratories, present an energy-economics perspective of SSL considering societal changes and SSL technology evolution. In a second article, Narukawa et al working at Nichia Corporation—the pioneer and still the leading company in SSL—describe the state of the art of current research products. They demonstrate record performance with white LEDs exhibiting luminous efficacy of 183 lm W ^-1 at high-current injection. Then, a series of topical papers discuss in detail various aspects of the physics and technology of white LEDs

  Carrier localization in InGaN quantum wells has been considered the key to white LEDs' success despite the huge density of defects. A comprehensive review of the different localization mechanisms and their implication for internal quantum efficiency (IQE) is proposed by Oliver and co-workers from Cambridge University. When discussing IQE in InGaN-based LEDs, the efficiency droop at high-current injection always emerges, which is a major concern for the future of SSL technology. Here, a collaborative work between Samsung and the Gwangju Institute of Science and Technology (Korea) proves that a specific design of the active region can limit this detrimental effect.

  Once the issue of the IQE is solved, one still has to let the photons out of the chip. Matioli and Weisbuch from the University of California at Santa Barbara introduce the use of photonic crystals (PhCs) to improve light extraction efficiency. They describe different approaches to overcoming the main limitation of LEDs when implementing surface PhCs.

  The technology of SSL, and in particular of colour rendering, is tackled by Zukauskas et al who studied in detail different white light sources. They show that extreme colour-fidelity indices need to cover the entire spectrum, with a broad-band at 530–610 nm and a component beyond 610 nm. Then, the reliability of GaN-based LEDs is discussed in the paper of Meneghesso and co-workers. The authors consider the most important physical mechanisms that are (i) the degradation of the active layer of LEDs, (ii) the degradation of the package/phosphor system, (iii) the failure of GaN-based LEDs against electrostatic discharge.

  Finally, GaN LEDs on silicon developed in the group of Egawa at the Nagoya Institute of Technology are presented. This technology could allow a significant decrease in the fabrication cost of white LEDs.

• Open/close Measurement of the ablated thickness of films in the launch of laser-driven flyer plates

  S Watson and J E Field 2000 J. Phys. D: Appl. Phys. 33 170 Tag this article

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  Laser-driven flyers were launched from substrate-backed aluminium films. The flyers were approximately 1 mm in diameter and a few micrometres thick and were produced by single pulses from a Q-switched Nd:YAG laser, of 10 ns full-width half-maximum and typically up to a few hundred millijoules energy. The ablated thickness of the film was measured using photo-emission spectroscopy to detect the vaporized tracer material in the laser-induced plasma: tracer layers of yttrium were deposited within the aluminium films at various depths, with sub-micrometre accuracy. Using this technique, the ablation depths were measured to be between 280 and 1100 nm for laser pulse energies between 50 and 156 mJ.

• Open/close Impact of photonic crystals on LED light extraction efficiency: approaches and limits to vertical structure designs

  Elison Matioli and Claude Weisbuch 2010 J. Phys. D: Appl. Phys. 43 354005 Tag this article

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  The enhancement of the extraction efficiency in light emitting diodes (LEDs) through the use of photonic crystals (PhCs) requires a structure design that optimizes the interaction of the guided modes with the PhCs. The main optimization parameters are related to the vertical structure of the LED, such as the thickness of layers, depth of the PhCs, position of the quantum wells as well as the PhC period and fill factor. We review the impact of the vertical design of different approaches of PhC LEDs through a theoretical and experimental standpoint, assessing quantitatively the competing mechanisms that act over each guided mode.

  Three approaches are described to overcome the main limitation of LEDs with surface PhCs, i.e. the insufficient interaction of low order guided modes with the PhCs. The introduction of an AlGaN confining layer in such structure is shown to be effective in extracting a fraction of the optical energy of low order modes; however, this approach is limited by the growth of the lattice mismatched AlGaN layer on GaN. The second approach, based on thin-film LEDs with PhCs, is limited by the presence of an absorbing reflective metal layer close to the guided modes that plays a major role in the competition between PhC extraction and metal dissipation. Finally, we demonstrate both experimentally and theoretically the superior extraction of the guided light in embedded PhC LEDs due to the higher interaction between all optical modes and the PhCs, which resulted in a close to unity extraction efficiency for this device.

  The use of high-resolution angle-resolved measurements to experimentally determine the PhC extraction parameters was an essential tool for corroborating the theoretical models and quantifying the competing absorption and extraction mechanisms in LEDs.

• Open/close Recent results on the degradation of white LEDs for lighting

  G Meneghesso et al 2010 J. Phys. D: Appl. Phys. 43 354007 Tag this article

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  Over the last years, GaN-based light-emitting diodes (LEDs) have been shown to be excellent candidates for the realization of high-efficiency light sources. White LEDs based on phosphor conversion can reach record efficiencies in excess of 150 lm W ⁻¹, as demonstrated by several manufacturers and research groups. However, the reliability of white LEDs is still limited by a number of issues that must be addressed before these devices can find wide application in the market. This paper gives an overview on the most important physical mechanisms that limit the reliability of GaN-based LEDs for application in solid-state lighting. Starting from general considerations on the reliability of state-of-the-art white LEDs, the following degradation mechanisms are described in detail: (i) the degradation of the active layer of LEDs due to increased non-radiative recombination and reverse-bias stress; (ii) the degradation of the package/phosphor system, with subsequent worsening in the chromatic properties of the LEDs; (iii) the failure of GaN-based LEDs submitted to electrostatic discharge events. The data presented in this paper are critically compared with those reported in the literature.

• Open/close Microstructural origins of localization in InGaN quantum wells

  R A Oliver et al 2010 J. Phys. D: Appl. Phys. 43 354003 Tag this article

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  The startling success of GaN-based light emitting diodes despite the high density of dislocations found in typical heteroepitaxial material has been attributed to localization of carriers at non-uniformities in the quantum wells (QWs) which form the active region of such devices. Here, we review the different possible structures within the QWs which could act as localization sites, at length scales ranging from the atomic to the tens of nanometre range. In some QWs several localization mechanisms could be operational, but the challenge remains to optimize the QWs' structure to achieve improved quantum efficiencies, particularly at high excitation powers.

• Open/close Microplasmas for nanomaterials synthesis

  Davide Mariotti and R Mohan Sankaran 2010 J. Phys. D: Appl. Phys. 43 323001 Tag this article

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  Microplasmas have attracted a tremendous amount of interest from the plasma community because of their small physical size, stable operation at atmospheric pressure, non-thermal characteristics, high electron densities and non-Maxwellian electron energy distributions. These properties make microplasmas suitable for a wide range of materials applications, including the synthesis of nanomaterials. Research has shown that vapour-phase precursors can be injected into a microplasma to homogeneously nucleate nanoparticles in the gas phase. Alternatively, microplasmas have been used to evaporate solid electrodes and form metal or metal-oxide nanostructures of various composition and morphology. Microplasmas have also been coupled with liquids to directly reduce aqueous metal salts and produce colloidal dispersions of nanoparticles. This topical review discusses the unique features of microplasmas that make them advantageous for nanomaterials synthesis, gives an overview of the diverse approaches previously reported in the literature and looks ahead to the potential for scale-up of current microplasma-based processes.