Defect state assisted tunneling in intermediate temperature molecular beam epitaxy grown GaAs

Current transport in molecular beam epitaxy (MBE) GaAs grown at low and intermediate growth temperatures is strongly affected by defects. A model is developed here that shows that tunneling assisted by defect states can dominate, at some bias ranges, current transport in Schottky contacts to unannealed GaAs material grown at the intermediate temperature range of about 400°C. The deep defect states are modeled by quantum wells which trap electrons emitted from the cathode before re-emission to semiconductor. Comparison of theory with experimental data shows defect states of energies about 0.5 eVbelow conduction band to provide the best fit to data. This suggests that arsenic interstitials are likely to mediate this conduction. Comparison is also made between as-grown material and GaAs grown at the same temperature but annealed at 600°C. It is suggested that reduction of these defects by thermal annealing can explain lower current conduction at high biases in the annealed device as well as higher current conduction at low biases due to higher lifetime. Quenching of current by light in the as-grown material can also be explained based on occupancy of trap states. Identification of this mechanism can lead to its utilization in making ohmic contacts, or its elimination by growing tunneling barrier layers.     

Quantitative meanings of verbal probability expressions.

The meanings of 18 verbal probability expressions were studied in 3 ways: (a) frequency distributions of what single number best represented each expression; (b) word-to-number acceptability functions from what range of numbers from 0% to 100% best represented each expression; and (c) number-to-word acceptability functions from which expressions were appropriate for multiples of 5% from 5% to 95%. These results agreed highly with others and were highly consistent across methods. Expressions incorporating the stem probable were quantitatively synonymous with expressions incorporating the stem likely. Except for expressions using the word chance, positive expressions (e.g., likely) were closer to 50% in meaning than corresponding negative expressions (e.g., unlikely). This method proved very useful in deriving fuzzy-set membership functions for probability words, encouraging us in our ongoing codification effort. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excerpts from Papers on Structures

This essay is part of an ongoing study of women in the architectural environment. It focuses on the perception of discrimination in the professional environment, family issues, career goals, and women's networks and support groups. This essay is the result of the compilation of two independent surveys taken in 1989 by female students at Tulane University School of Architecture. The first survey covered all the female graduates from the School of Architecture; the subsequent survey sought to challenge the responses to the first and addressed 87 male architects practicing in the New Orleans metropolitan area. While responses to these two surveys are interesting in themselves, combining the often disparate perspectives is illuminating. Of particular interest are the cases where conflicting responses were received from women and men working in the same architectural office. This essay seeks to address the critical discrepancies that exist in the perception of women's current roles in the field of architecture.     

An EIA/CEA-909 compatible smart antenna system for digital terrestrial broadcasting applications

This paper discusses the theory and design of a smart antenna system for receiving digital terrestrial television signals. The pertinent antenna theory and the associated hardware is presented as is the relationship between the two. Finally, field results using digital terrestrial television signals are presented to evaluate the performance of the smart antenna system.     

Some comments on "Scientific method and the adversary model."

Suggests that the adversary model of research advocated by M. Levine (see record 1977-09339-001), which is based on legal procedures for arriving at truth, is appropriate for initial hypothesis construction and not as an alternative to rigorous experimental investigation. A reply by Levine follows. (PsycINFO Database Record (c) 2010 APA, all rights reserved)