High performance GaAs MESFETs with molecular implanted and optimized lowly-doped drain structure for maximized speed, gain and breakdown performance

GaAs MESFETs with novel lowly-doped drain structures have been developed utilizing molecular implants of silicon trifluoride. Short-channel effects in the 1/4 μm enhancement- and depletion-mode transistors have been suppressed with drain-induced barrier height lowering of less than 70 mV/V and pinch-off voltage shifts of less than 220 mV as the gate length was scaled from 1.0 to 1/4 μm. The 3-terminal breakdown, the transconductance to output conductance ratio, and the unity current gain, cut-off frequency were simultaneously optimized. The E-mode device possessed breakdown of >10 V, G_m · R_ds > 9.5, F_t > 55 GHz, and nominal on-resistance of 2.1 Ω mm while the D-mode device had breakdown >10 V, G_m · R_ds > 6.0, F_t > 45 GHz, and nominal on-resistance of 1.9 Ω mm. These optimized transistors enabled the realization of a variety of low-power digital and high-power mixed signal circuits, using 3-level source-coupled transistor and common-mode logic, such as laser and electro-optic drivers, highly integrated transceivers, multiplexers, demultiplexers, and clock data recover circuits.     

Covering Radius 1985–1994

 We survey important developments in the theory of covering radius during the period 1985–1994. We present lower bounds, constructions and upper bounds, the linear and nonlinear cases, density and asymptotic results, normality, specific classes of codes, covering radius and dual distance, tables, and open problems. Received October 28, 1994; revised version May 28, 1996     

The afferent neural response to electrotactile stimuli: preliminary results.

We recorded action potentials from three RA fibers innervating primate fingerpad, while applying electrotactile (electrocutaneous) stimulation. Negative pulses required 1.3-1.5 times more current than positive ones for entrainment. The strength-duration time constant was approximately 151 micros. Suprathreshold sinusoidal vibration synchronized to 30-Hz electrotactile pulses changed the electrotactile entrainment current slightly, indicating a possible electrical-mechanical transduction interaction.     

Low-cost, multi-GHz electrical packaging for serial optoelectroniclinks utilizing vertical cavity surface emitting lasers

Recent advances in semiconductor laser technology, specifically the emergence of vertical cavity surface emitting lasers (VCSELs), have created room for substantial improvements in the performance of low-cost, fiber-optic links. However, traditional electronic packaging of the VCSELs and detectors severely limits the performance of these new devices. In two previous papers from this laboratory [1996, 1997], traditional laser packages were described, modeled, measured and evaluated. Further, a new improved conceptual package, referred to as the optical package for advanced lasers (OPAL), was presented, as were a set of design guidelines for a new generation of packages for VCSELs and detectors. This paper, describing a continuation of the previous work, discusses the design, modeling, fabrication, and demonstration of OPALs in a laboratory environment. Measured results recorded from VCSELs packaged in OPALs operating to 5 Gbit/s data rates are presented     

The use of remotely sensed data to detect channel hydromorphology; River Tummel,Scotland

Colour aerial photography and multi‐spectral imagery acquired from airborne platforms for the River Tummel, Scotland, was used in conjunction with field survey to assess the feasibility of monitoring hydromorphology and human alteration within the river corridor. The study was undertaken to investigate the possibility of remotely sensing the physical status of a nation's rivers at the national scale to comply with the requirement of the European Water Framework Directive. Visual assessment and unsupervised and supervised automated classifications of the imagery were undertaken and compared with field survey data. In the absence of overhanging vegetation canopies most features above the water line of interest were visible on the imagery. Below the water line, morphology and substrate composition together with bank materials on vertically cut banks are less easily detected. The overall accuracy of automated classification procedures, compared to field survey, was 60% for the colour aerial photography and 68% for the multi‐spectral imagery. Supervised classification was superior to unsupervised classification procedures. Sun glint on water surfaces and shadows caused by high banks, trees and buildings were observed as the cause of most misclassification of features. Overall, the study demonstrates that remotely sensed digital imagery has the potential to allow panoptic mapping of river hydromorphology and human impacts. The possibilities and constraints, in light of the findings of this study, are discussed. In the context of new legislation which requires environmental protection agencies to have robust tools for monitoring the physical status, as part of meeting the objective of good ecological status, of rivers across an entire nation, remote sensing appears to provide a way forward. Copyright © 2004 John Wiley & Sons, Ltd.     

Reaction engineering studies of methane coupling in fluidised-bed reactors

The oxidative coupling of methane has been conducted in 30 and 60mm dia. fluidised-bed reactors. Methane conversions as high as 40% were achieved at isothermal conditions using methane/oxygen mixtures without diluents. At the same contact time the two reactors had similar selectivities to hydrocarbons. At 850°C the hydrocarbon selectivity decreased dramatically with increasing contact time but this effect was much less severe at lower temperatures. Axial gas concentration profiles through the catalyst bed in the 60mm reactor indicated that at 850°C there was a rapid consumption of oxygen and formation of products in the bottom section of the bed followed by a net loss of hydrocarbon in the oxygen-free zone. This loss was due to carbon formation on the catalyst which was circulated back to the oxygen-containing zone of the bed where the carbon was combusted.     

Evolution of silicon bulk lifetime during III–V‐on‐Si multijunction solar cell epitaxial growth

The evolution of Si bulk minority carrier lifetime during the heteroepitaxial growth of III–V on Si multijunction solar cell structures via metal‐organic chemical vapor deposition (MOCVD) has been analyzed. In particular, the impact on Si lifetime resulting from the four distinct phases within the overall MOCVD‐based III–V/Si growth process were studied: (1) the Si homoepitaxial emitter/cap layer; (2) GaP heteroepitaxial nucleation; (3) bulk GaP film growth; and (4) thick GaAs_yP_1‐y compositionally graded metamorphic buffer growth. During Phase 1 (Si homoepitaxy), an approximately two order of magnitude reduction in the Si minority carrier lifetime was observed, from about 450 to ≤1 µs. However, following the GaP nucleation (Phase 2) and thicker film (Phase 3) growths, the lifetime was found to increase by about an order of magnitude. The thick GaAs_yP_1‐y graded buffer was then found to provide further recovery back to around the initial starting value. The most likely general mechanism behind the observed lifetime evolution is as follows: lifetime degradation during Si homoepitaxy because of the formation of thermally induced defects within the Si bulk, with subsequent lifetime recovery due to passivation by fast‐diffusing atomic hydrogen coming from precursor pyrolysis, especially the group‐V hydrides (PH₃, AsH₃), during the III–V growth. These results indicate that the MOCVD growth methodology used to create these target III–V/Si solar cell structures has a substantial and dynamic impact on the minority carrier lifetime within the Si substrate. Copyright © 2015 John Wiley & Sons, Ltd.     

Density,production, and survival of walleye (Sander vitreus) eggs in the Muskegon River,Michigan

Walleye (Sander vitreus) is an important sport fish in the Great Lakes that is experiencing low reproductive success after severe population declines starting in the late 1940s. In the Muskegon River, Michigan, natural reproduction of walleyes remains low and is largely supplemented by stocking. To determine factors influencing walleye reproductive success in the Muskegon River, we estimated walleye egg survival using insitu egg incubators covered with nitex screening (2003–2004) and estimated density and survival of fertilized eggs caught on furnace filter traps across different substrate types (2005–2006). We compared physical habitat suitability for walleye eggs under high and low flow scenarios. Density of walleye eggs was highest in regions of gravel/cobble substrates. Egg survival was higher in egg incubators (24–49.5%) than on furnace filter traps (2.0%), suggesting predation is an important source of walleye egg mortality in the Muskegon River. Cold water temperatures that extended developmental stage durations may also be an important source of egg mortality. The dynamic habitat suitability model predicted low suitability for eggs due to poor temperature and velocity conditions. Despite low egg survival rates, 40 million to 1 billion eggs were estimated to hatch. The low natural reproduction of walleyes in the Muskegon River is likely due to a combination of low walleye egg survival and failure of walleye larvae to reach their nursery grounds in Muskegon Lake.     

Are toxicological responses in laboratory (inbred) zebrafish representative of those in outbred (wild) populations? - A case study with an endocrine disrupting chemical

Laboratory animals tend to be more inbred and less genetically diverse than wild populations, and thus may differ in their susceptibility to chemical stressors. We tested this hypothesis by comparing the responses of related inbred (theoretical inbreeding F(IT) = n + 0.25) and outbred (F(IT) = n) zebrafish (Danio rerio) WIK/Wild family lines to an endocrine disrupting chemical, clotrimazole. Exposure of inbred and outbred zebrafish to 2.9 μg clotrimazole/L had no effect on survival, growth, or gonadal development. Exposure of both lines to 43.7 μg clotrimazole/L led to male-biased sex ratios compared with controls (87% versus 55% and 92% vs 64%, for inbred and outbred males, respectively), advanced germ cell development, and reduced plasma 11-ketotestosterone concentrations in males. However, outbred males (but not inbred males) developed testis that were more than twice the weight of controls, which corresponded with a proliferation of Leydig cells and maintenance of the expression (rather than down-regulation occurring in inbreds) of gonadal aromatase (cyp19a1a) and insulin-like growth factor (igf1). Our results illustrate that the effects of an endocrine disrupting chemical (clotrimazole) on some end points (here testis development) can differ between inbred and outbred zebrafish. This highlights the need for reporting pedigree/genetic information and consistency in the responses of laboratory animals (e.g., by using model compounds as positive controls).