TCAD simulation of ion implantation test for controlling quality of GaAs substrates used for fabricating implanted devices

The quality of GaAs substrate material for manufacturing ion implanted devices is routinely determined by an ion implantation test. The test involves measuring an electrical quantity, such as sheet resistance, after implanting Si into the substrate. This work employs GaAs TCAD simulation to address the range of validity of the implantation test and the pitfalls associated with it. The results show that the electrical measurements are capable of discerning typical variation in the carbon concentration in the substrate. But, the surface or interface charge on GaAs, which may result from processing involved in wafer preparation, is also important. Therefore, while the implantation test in most cases is adequate to control the quality of the substrate, the test is susceptible to misinterpretation owing to the variations arising from the process involved in wafer preparation for the test.     

The combined effects of band-to-band tunneling and impactionization in the off regime of an LDD MOSFET

Fully self-consistent two-dimensional simulation of band-to-band tunneling (BTBT) in a lightly doped drain (LDD) MOSFET is reported. The simulation results are compared to experimental data and explain the observed current leakage effects. At low drain bias the leakage currents in the off regime can be explained by BTBT alone. At high drain bias and at deep subthreshold gate bias the leakage current is increasingly due to avalanche generation by carriers created initially in BTBT and accelerated subsequently in the high electric fields     

Unconventional complexity measures for unconventional computers

Unconventional computers—which may, for example, exploit chemical/analogue/quantum phenomena in order to compute, rather than electronically implementing discrete logic gates—are widely studied in both theoretical and practical contexts. One particular motivation behind unconventional computation is the desire efficiently to solve classically difficult problems—we recall chemical-computer attempts at solving NP -complete problems such as the Travelling Salesperson Problem—, with computational complexity theory offering the criteria for judging this efficiency. However, care must be taken here; conventional (Turing-machine-style) complexity analysis is not always appropriate for unconventional computers: new, non-standard computational resources, with correspondingly new complexity measures, are often required. Accordingly, we discuss in the present paper various resources beyond merely time and space (and, indeed, discuss various interpretations of the term ‘resource’ itself), advocating such resources’ consideration when analysing the complexity of unconventional computers. We hope that this acts as a useful starting point for practitioners of unconventional computing and computational complexity.     

A study of solid-aqueous equilibria by the speciation approach in the hydronium alunite-sulfuric acid-water system at high temperatures

An experimental and theoretical investigation of the aqueous equilibria of hydronium alunite-sulfuric acid-water systems at saturation and under pressure leaching conditions was conducted. To this end, pure hydronium alunite was synthesized through anin situ dissolution-precipitation reaction sequence. A nonideal chemical equilibrium model was then developed to predict the behavior of the system at high acidities (pH_{25 °C} < 1) and high temperatures (230 °C to 270 °C). The model was based upon the most recent thermodynamic data available for all known aluminum-oxy-hydroxyl-sulfate-bisulfate species, as well as experimentally determined solubility data for hydronium alunite. System behavior was characterized by speciation diagrams which illustrated the relative concentrations of aqueous species and acidity as functions of total sulfate concentration. This type of investigation was found to give valuable insight into the equilibrium behavior of high-temperature systems that would be otherwise inaccessible.     

Charge-limited domains in gallium-arsenide avalanche diodes

An analysis of the high-efficiency mode of operation of gallium-arsenide avalanche diodes is presented. The concept of a charge-limited domain is introduced, and it is shown that the occurrence of this domain effectively increases the velocity of the travelling charges. This velocity increase occurs at a point roughly midway through the transit time, and causes an increase in the induced particle current at that time. This effect, coupled with the effects of depletion-layer-width modulation, has an important bearing on the observed high efficiency of nonpunchedthrough `clump? and `hi-lo? gallium-arsenide structures.     

Propagating avalanche-zone mode for high-efficiency GaAs lo?hi?lo IMPATT structures

The superiority of high-efficiency hi?lo and lo?hi?lo impatt structures over conventional structures and the distinctive tuning characteristics of these structures have been largely explained in terms of a variety of drift-region mechanisms common to both structures. There are, however, sometimes distinct differences between the large-signal behaviour of the two structures, and these have not been explained so far. In the letter, a reason for the differences is suggested: it is shown that large-signal impatt oscillations may trigger a `propagating avalanche-zone mode? in lo?hi?lo structures, but that this will not happen in hi?lo structures. The existence of such a mode is thought to be capable of explaining observed differences between the large-signal properties of the two structures.     

An automated competency-based model for teaching skills in the administration of the WAIS—R.

An assessment of the effectiveness of an automated version of the Mastery Model (a competency-based [CB] training model) for training skills in the administration of the WAIS—R to 22 graduate psychology students indicated that this automated version was an effective training procedure. The training cost of this method was 50% less than the nonautomated version and was rated by Ss as a highly favorable training procedure. The authors discuss how this type of automated CB training procedure is a viable response to the professional mandates for CB clinical training. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calculation of dielectric-aerial-radiation patterns

Brown and Spector's theory of the dielectric-rod aerial is extended and refined by considering the effect of the rod on the feed-radiation pattern. A correction function is deduced which includes an additional phase-correction term.     

Criterion for the optimum punchthrough factor of gallium-arsenide IMPATT diodes

Simple theory predicts an optimum punchthrough factor of approximately 0.7 for gallium-arsenide IMPATTs. Computer-simulation results demonstrate good general agreement with the predictions of the theory.