The effects of nonlocal impact ionization on the speed of avalanche photodiodes

The nonlocal enhancement in the velocities of charge carriers to ionization is shown to outweigh the opposing effects of dead space, increasing the avalanche speed of short avalanche photodiodes (APDs) over the predictions of a conventional local model which ignores both of these effects. The trends in the measured gain-bandwidth product of two short InAlAs APDs reported in the literature support this result. Relatively large speed benefits are predicted to result from further small reductions in the lengths of short multiplication regions.     

Inside Front Cover: The Elastic Properties and Plastic Behavior of Two‐Dimensional Polymer Structures Fabricated by Laser Interference Lithography (Adv. Funct. Mater. 10/2006)

The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern.     

Design procedure of class-E amplifier for off-nominal operation at 50% duty ratio

Design equations for satisfying the off-nominal operating condition [i.e., only the zero-voltage switching (ZVS) condition] of the Class-E amplifier with a linear shunt capacitance at a duty ratio D=0.5 are derived. A new parameter s (V/s), called the slope of switch voltage when the switch turns on is introduced to obtain an image of the distance from the nominal conditions. By examining off-nominal Class-E operation degree of the design freedom of the Class-E amplifier increases by one. In addition various amplifier parameters such as operating frequency, output power, and load resistance range can be set as design specifications. For example, the peak switch voltage and switch current can be taken into account in the design procedure. Examples of a design procedure of the Class-E amplifier for off-nominal operation are given. The theoretical results were verified with PSpice simulation and experiments.     

The Influence and Interpretation of Surface Parameters for Wetting Transitions in Ternary Mixtures

Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms.     

Curie Temperatures of III–V Diluted Magnetic Semiconductors Calculated from First-Principles in Mean Field Approximation

Electronic structure and ferromagnetism in III–V compound-based diluted magnetic semiconductors (DMS) are investigated based on first-principles calculations by using the Korringa-Kohn-Rostoker method combined with the coherent-potential-approximation. The stability of the ferromagnetic phase in GaN-, GaAs-, GaP-, GaSb-based DMS is investigated systematically. The calculations show that 3d-impurities from the first-half of the transition metal series favor the ferromagnetic state, while impurities from the latter-half of the series exhibit spin-glass behavior. This chemical trend in the magnetism is explained by the double exchange mechanism taking the local symmetry at the impurity gap states into account. Curie temperatures of GaAs- and GaN-based DMS are estimated by using the Heisenberg model in a mean field approximation with the parameters calculated from first-principles. It is suggested that room-temperature ferromagnetism can be realized in these systems.     

A CMOS multichannel 10-Gb/s transceiver

We describe a CMOS multichannel transceiver that transmits and receives 10 Gb/s per channel over balanced copper media. The transceiver consists of two identical 10-Gb/s modules. Each module operates off a single 1.2-V supply and has a single 5-GHz phase-locked loop to supply a reference clock to two transmitter (Tx) channels and two receiver (Rx) channels. To track the input-signal phase, the Rx channel has a clock recovery unit (CRU), which uses a phase-interpolator-based timing generator and digital loop filter. The CRU can adjust the recovered clock phase with a resolution of 1.56 ps. Two sets of two-channel transceiver units were fabricated in 0.11-/spl mu/m CMOS on a single test chip. The transceiver unit size was 1.6 mm /spl times/ 2.6 mm. The Rx sensitivity was 120-mVp-p differential with a 70-ps phase margin for a common-mode voltage ranging from 0.6 to 1.0 V. The evaluated jitter tolerance curve met the OC-192 specification.     

High resistivity measurement of SiC wafers using different techniques

To establish fast, nondestructive, and inexpensive methods for resistivity measurements of SiC wafers, different resistivity-measurement techniques were tested for characterization of semi-insulating SiC wafers, namely, the four-point probe method with removable graphite contacts, the van der Pauw method with annealed metal and diffused contacts, the current-voltage (I-V) technique, and the contactless resistivity-measurement method. Comparison of different techniques is presented. The resistivity values of the semi-insulating SiC wafer measured using different techniques agree fairly well. As a result, application of removable graphite contacts is proposed for fast and nondestructive resistivity measurement of SiC wafers using the four-point probe method. High-temperature van der Pauw and room-temperature Hall characterization for the tested semi-insulating SiC wafer was also obtained and reported in this work.     

Web Services Architecture

The underlying need for Web Services has been demonstrated by their early adoption and rapid evolution during the last few years. This evolution has resulted in a number of specifications being proposed that at first glance seem independent of one another. The current immaturity of the base technology and the growing number and diversity of specifications related to Web Services is sometimes seen as a barrier to developers attempting to combine them to create a working piece of software. For some, the apparent lack of stability and coherence in the specifications even raises the question of the real long-term viability and value of the technology. This document puts those specifications into perspective by describing the set of interoperable XML protocols that are the foundation of building interoperable systems, middleware, and applications. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metastable phase relation and phase equilibria in the Cr2O3-Fe2O3 system

In order to ascertain the metastable phase relation in the Cr₂O₃-Fe₂O₃ system, the existing phases were investigated by X-ray analysis using samples obtained by heating the coprecipitated powders for 1 h at 600–1000°C. There was a metastable two-phase region of Cr₂O₃-rich (CC) and Fe₂O₃-rich (FC) phases below about 940°C. Equilibrium state of 1:1 composition at 600–900°C was considered to be a single phase of the corundum solid solution. The metastable two-phase CC + FC region was suggested to appear probably due to the compositional inhomogeneity in the coprecipitated powders.     

Experimental characterisation of the drying effect on uniaxial mechanical behaviour of mortar

The main objective of this present study was to evaluate, for a standard mortar, the drying effect on its mechanical behaviour. Numerous uniaxial compression tests were thus performed with loading-unloading cycles. They were carried out on different samples previously preserved under various conditions of conservation: preserved from desiccation, air drying and rapid drying at 60°C. The obtained results showed significant influences of these conditions on the material behaviour (increase in strength, decrease in Young's modulus and Poisson's ratio) and the necessity of taking into account the coupling effects between mechanical—poromechanical behaviours and drying.