Progress toward nanoscale silicon light emitters

Impressive advances have been made over the last few years in teaching silicon how to emit light. Recently, light-emitting devices (LEDs) made of porous silicon and other forms of nanoscale silicon have been demonstrated with specifications that start to make them attractive for commercial applications. This paper reviews the state-of-the-art in the materials science and device properties of nanoscale silicon-based LED's, including their integration with microelectronic circuits. Porous silicon and other forms of nanoscale silicon contain crystallites smaller than 10 nm. Their intrinsic optical properties are dominated by quantum confinement, which produces an opening of the bandgap and an increase of the luminescence energy with decreasing nanocrystal sizes. The mechanical, thermal, and electrical properties of porous silicon are strongly degraded compared to those of bulk crystalline silicon. In addition, special techniques should be used to maintain a good passivation of the internal surface and the mechanical integrity of porous silicon. As a result, the design and optimization of LEDs made of nanoscale silicon is difficult. The stability, efficiency, response time, and spectral characteristics of porous silicon LEDs are discussed. The progress toward the integration of porous silicon LEDs with microelectronic circuits is reviewed and a simple alphanumeric display is shown     

Error and flow control in terabit intelligent optical backplanes

The design of a free-space optical backplane which supports error and flow control functions is described. Traditionally, these functions are implemented in custom high-speed electronic application specific integrated circuits, which are physically removed from the optical interconnect layer. In this paper, we consider migrating these functions directly into the optoelectronic layer, yielding an “intelligent optical backplane.” Conventional error control protocols are infeasible with optical backplanes since they require excessive amounts of hardware. The design of an efficient error control protocol based upon a multidimensional parity check, along with the effective flow control protocol is proposed and analyzed. The key blocks of the protocol have been implemented in 0.8- and 0.5-μm CMOS/SEED devices and are summarized. The protocols require significantly less hardware than alternative schemes, and smart pixel arrays supporting these protocols are scalable to higher bandwidths and lower latencies. A very large scale integration analysis indicates that using 2004 technology, a free-space backplane can potentially be clocked at 1 GHz and support 24 Tb/s of bandwidth. Finally, the proposed error control protocols should be useful in optical disks and holographic memory systems, which also perform error control on large two-dimensional arrays of optical bits     

Polymer thermosetting organic light-emitting devices

We report a systematic study of novel single- and double-layer thermosetting light-emitting devices (LED's) based on triarytamines for hole transport layer and fluorenes for the emitting and electron transport layer. These devices possess high-thermal stability, high-quantum efficiency, and high-bandgap emission (blue and green). We have fabricated dot matrix displays based on analogs of these materials     

Design and applications of silica-based planar lightwave circuits

Planar lightwave circuits (PLCs) are waveguide devices that integrate fiber-matched optical waveguides on silicon or glass substrate to provide an efficient means of interaction for the guided-wave optical signals, PLCs provide various important and functional devices for optical wavelength-division multiplexing, time-division-multiplexing systems, and subscriber networks. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating multiplexers, optical add-drop multiplexers and hybrid optoelectronics integration technologies     

Spectroscopic study of red light emission in porous silicon

Since bulk silicon does not emit light in the visible part of the spectrum, the discovery of visible luminescence from porous silicon has been quite surprising and has generated significant interest. This material differs from bulk silicon in one important way, in that it consists of interconnected silicon nanostructures, having very large surface to volume ratios. The first emission mechanism proposed involved carrier recombination within quantum size silicon particles, but more recent work has shown that surface emission models may be more likely. The problems with the quantum confinement model will be discussed in view of current data, and an oxygen center luminescence model will be discussed, with supporting experimental data. A direct correlation between the presence of these centers and the red photoluminescence in both as-made and oxidized PSi will be presented     

Silicon photonics

The silicon chip has been the mainstay of the electronics industry for the last 40 years and has revolutionized the way the world operates. Today, a silicon chip the size of a fingernail contains nearly 1 billion transistors and has the computing power that only a decade ago would take up an entire room of servers. As the relentless pursuit of Moore's law continues, and Internet-based communication continues to grow, the bandwidth demands needed to feed these devices will continue to increase and push the limits of copper-based signaling technologies. These signaling limitations will necessitate optical-based solutions. However, any optical solution must be based on low-cost technologies if it is to be applied to the mass market. Silicon photonics, mainly based on SOI technology, has recently attracted a great deal of attention. Recent advances and breakthroughs in silicon photonic device performance have shown that silicon can be considered a material onto which one can build optical devices. While significant efforts are needed to improve device performance and commercialize these technologies, progress is moving at a rapid rate. More research in the area of integration, both photonic and electronic, is needed. The future is looking bright. Silicon photonics could provide low-cost opto-electronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects, as well as emerging areas such as optical sensing technology and biomedical applications. The ability to utilize existing CMOS infrastructure and manufacture these silicon photonic devices in the same facilities that today produce electronics could enable low-cost optical devices, and in the future, revolutionize optical communications.     

Development of high efficiency GaN-based multiquantum-welllight-emitting diodes and their applications

Highly efficient GaInN-GaN multiple quantum-well (MQW) light-emitting diodes (LEDs) were successfully developed by the low-temperature AlN buffer layer method for metal-organic vapor phase epitaxy (MOVPE). The light-emitting layer of the GaInN-GaN MQW drastically enhances the performance of GaN-based LEDs in terms of the efficiency and spectrums. Flip-chip (FC) type MQW LEDs have been newly developed to increase efficiency in extracting light from the GaN-based crystal to the outside. The luminous intensities of FC type blue and green LEDs are typically 6 and 14 cd, respectively, at 20 mA. The output power of the FC-type LEDs was 14 mW at 20 mA, which was approximately two times higher than that of the conventional face-up type blue LEDs. The external quantum efficiency of blue FC-type LEDs was as high as 20% at 20 mA. New multicolor package was developed using these high performance nitride-based LEDs and commercial AlGaInP-based red LEDs, the color range of which is the largest among other flat panel display devices     

Silicon oxynitride planar waveguiding structures for application inoptical communication

The refractive index of silicon oxynitride (SiON), a widely used material for integrated optics devices, can be chosen in a wide range between 1.45-2.0. We describe how the consequent large design freedom can be exploited on the one hand for a “standard” polarization independent optical channel waveguide having a favorable tradeoff between efficient fiberchip coupling and small bend radii (compact devices) and on the other hand for special-purpose and hybrid components where the refractive index should be finely adjusted for obtaining the desired functionality. We illustrate the applicability of SiON by describing a few devices for optical filtering in a new architecture for wavelength multiplexing, modulation, polarization splitting and second-harmonic generation     

Visible and 1.54 m Emission From Amorphous Silicon Nitride Films by Reactive Cosputtering

In this paper, we present our main results on the structural and optical properties of light-emitting amorphous silicon nitride ($hbox{SiN}_{x}$) films fabricated by reactive magnetron cosputtering. In particular, we discuss the origin of the visible emission in amorphous silicon nitride films and investigate the optical emission properties of Erbium-doped amorphous silicon nitride ( $hbox{Er:SiN}_{x}$). The mechanisms of Er excitation and de-excitation in $hbox{Er:SiN}_{x}$ are discussed in relation to the engineering of efficient light sources at 1.54 $mu$m for on-chip nanophotonics applications. These results suggest that Er-doped amorphous silicon nitride films have a large potential for the fabrication of optically active photonic devices based on the Si technology.      

Raman-based silicon photonics

This paper reviews recent progress in a new branch of silicon photonics that exploits Raman scattering as a practical and elegant approach for realizing active photonic devices in pure silicon. The large Raman gain in the material, enhanced by the tight optical confinement in Si/SiO2 heterostructures, has enabled the demonstration of the first optical amplifiers and lasers in silicon. Wavelength conversion, between the technologically important wavelength bands of 1300 and 1500 nm, has also been demonstrated through Raman four wave mixing. Since carrier generation through two photon absorption is omnipresent in semiconductors, carrier lifetime is the single most important parameter affecting the performance of silicon Raman devices. A desired reduction in lifetime is attained by reducing the lateral dimensions of the optical waveguide, and by actively removing the carriers with a reverse biased diode. An integrated diode also offers the ability to electrically modulate the optical gain, a unique property not available in fiber Raman devices. Germanium-silicon alloys and superlattices offer the possibility of engineering the otherwise rigid spectrum of Raman in silicon.     

Control batteries: power system life savers

If protective devices and relays represent the ≫OPEN "nerves” of a medium- or high-voltage electric power system, the DC control battery distribution system represents the system's “bloodstream.” The battery distribution system delivers energy the battery provides to the control circuits of AC circuit breakers and other electrically operated interrupting equipment (the “muscle” of the electric power system), allowing operation. The battery is the DC power distribution system's “heart.” Reliable control battery systems assure proper functioning of well designed, installed, and maintained power systems. Battery system failure jeopardizes a power system by eliminating the DC control power source for AC system circuit breakers and protective devices. Failure to protect DC system components also could result in disastrous consequences for the battery system itself. The author discusses battery faults, battery protection, and battery maintenance. Battery charger faults and protection are also briefly mentioned, as are load protection, and DC system protection     

Efficient optical coupling between a polymeric waveguide and anultrafast silicon MSM photodiode

One task of the integration of optoelectronic functions with silicon devices is the construction of an optical waveguide on Si and the optical coupling of this waveguide to a silicon photodetector. We have fabricated polymeric strip waveguides on Si and demonstrate a very efficient design for the optical coupling between the polymeric waveguide and an ultrafast Si-based metal-semiconductor-metal (MSM) mesa-type photodetector. This detector uses high-quality epitaxial Si as the sensitive layer, which is sandwiched between two metallic contacts. If these MSM detectors are excited by a vertically incident free beam of λ=840 nm and pulses of 100-fs full-width at half-maximum (FWHM), they respond with electrical pulses of 3, 5-ps length (FWHM, T=300 K)     

Discrimination of the road condition toward understanding ofvehicle driving environments

The detection of vehicle driving environments is necessary to secure transport facilities safe from accidents and to keep the performance smooth. The road condition is one of the most important factors toward detection of vehicle driving environments. Conventional discrimination methods for road conditions involved the use of optical or ultrasonic sensors. However, since these sensors can only provide spot information, detected results do not always reflect the spacious condition. To deal with this problem, a new algorithm that employs image analysis technology for discrimination of road conditions is proposed in this paper. In this algorithm, for discrimination of road conditions, we focused on features related to water and snow on the road, and we extracted these features by image analysis. Features related to water were extracted by the ratio of horizontal polarization image intensity to vertical polarization image intensity for each pixel. Features related to snow were extracted by texture analysis using the co-occurrence matrix. We employ a multivariate analysis to discriminate five kinds of the road conditions: “Dry,” “Wet,” “Slushy,” “Icy” and “Snowy,” on the basis of these features extracted from the road images as well as temperature. Furthermore, we conducted field tests to verify the accuracy of this algorithm and obtained favorable discrimination accuracy rate of 92.3% on the average     

Rare-earth-doped GaN: growth, properties, and fabrication of electroluminescent devices

A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N/sub 2/ source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc- and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 /spl mu/m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization.     

High-efficiency white phosphorescent polymer light-emitting devices

White phosphorescent light emission from polymer light-emitting devices (PLEDs) has been demonstrated. To fabricate the white-emitting PLED, blue phosphorescent polymer (BPP) and red phosphorescent polymer (RPP) were used for the emissive layer, and the emission color was tuned by controlling the concentration ratio of BPP to RPP. The external quantum efficiency of the white-emitting PLED, with CIE coordinates of (0.34, 0.36), was 6.0% at luminance of 100 cd/m/sup 2/. To investigate the emission mechanism in the PLED, its photoluminescence spectrum and transient decay were measured. These experimental measurements indicate that direct excitation of the iridium-complex (Ir-complex) units by carrier trapping is a major excitation process for white-emitting PLED. A 3.6-in full-color display based on the white phosphorescent PLED and color filters was demonstrated.     

Advances in AlGaInN blue and ultraviolet light emitters

In this paper, we discuss the current status and the considerable challenges for extending the nitride light sources into deeper ultraviolet (UV). We also review recent progress in exploratory blue and near UV III-nitride light emitters, such as vertical cavity devices and dual-wavelength light-emitting diodes, which may provide useful device templates for applications in the deeper UV     

Electromagnetic noise spectrum caused by partial discharge in airat high voltage substations

The authors investigated the characteristics of the electromagnetic spectrum caused by partial discharges (PDs) in air at three different types of high-voltage substations. From the measured results, they characterized the electromagnetic noise spectrum depending on the type of substation. They also measured the long-term change of the average gain of the noise spectrum and discussed the influence of atmospheric conditions on the results. Moreover, they introduced the “equivalent charge (q_e)” which was derived by converting the electric field strength estimated from the average gain into the charge magnitude of PD. They also proposed a “phase gate control method” for better understanding the electromagnetic noise spectrum characteristics and the mechanism causing electromagnetic waves from PDs     

Vacuum insulator flashover mechanisms, diagnostics and designimplications

This paper presents an approach for obtaining science-based answers to practical vacuum device problems. The question “How to translate scientific knowledge to design and operation practice” is rephrased to the more productive question “What research activities are required to provide science-based answers to practical problems!” Such activities involve the study of operational mechanisms in realistic, geometries with the help of appropriate diagnostics. Within this framework, recent research developments on vacuum insulator flashover are reviewed, with emphasis on the implications for device performance and design. Secondly, an overview is given of recent research activities performed at the Eindhoven University of Technology. By studying the relationship between flashover mechanisms and insulator performance, and the relationship between insulator performance and design, we aim at improved device performance, the formulation of guidelines, and the development of device diagnostics, for dc and ac vacuum devices     

From generic restoration actions to specific restoration strategies

The results presented here reflect work, extending over several years, to identify features underlying restoration processes that are common to almost all utilities and that can serve as guides for preparing and evaluating restoration plans, for developing expert system programs that will be widely useful, and ultimately for improving the effectiveness of restoration practices. Generality is achieved by identifying constituent elements of the process, namely a “target system”, “restoration building blocks (RBBs)”, “generic restoration actions (GRAs)”, and process constraints, and the factors that distinguish among three clearly demarcated stages. This distillation of the constituent elements of the restoration process provides a basis for development of a comprehensive, knowledge-based restoration expert system appropriate to a broad spectrum of power system utilities