Microwave properties of silicon junction tunnel diodes grown bymolecular beam epitaxy

The bias dependence of the single-port microwave reflection gain of 15 μm-diameter Si Esaki tunnel diodes, grown by molecular beam epitaxy, was studied as a function of frequency. A simple equivalent circuit accurately modeled the data and yielded the forward-bias junction capacitance, which cannot be obtained by conventional low frequency capacitance-voltage techniques. The diodes were highly-doped step p-i-n junctions and exhibited a peak current density of 16 kA/cm ². The microwave reflection gain and cut-off frequency were 12 dB land 1.6 GHz, respectively, with a speed index (slew rate) of 7.1 V/ns     

Review of Theories of Perception and the Concept of Structure.

Reviews the book "Theories of perception and the concept of structure," by Floyd H. Allport (see record 1955-15035-000). This book is in reality two books. The author planned it as one. The first twenty chapters give us a critical survey of many theories of perception while the last chapter presents the author's very original concept of "structure" which may be applied to, but does not necessarily arise out of, discussions of perception. He has certainly done a conscientious job on each of the thirteen major theories-ranging from the Titchenerian core-and-context, to the cybernetics of Wiener and of Pitts and McCulloch, and including such variety as the Gestalt, the Hebb cell-assembly, Helson adaptation level, Brunswik probabilistic, and the Bruner et al, directive-state. To give a touch of concreteness to his highly abstract theory of event structures, Allport suggests a simple mechanical model or analogue, a visualized schema. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reducing non-determinism of k-NN searching in non-ordered discrete data spaces

We propose a generalized version of the Granularity-Enhanced Hamming (GEH) distance for use in k-NN queries in non-ordered discrete data spaces (NDDS). The use of the GEH distance metric improves search semantics by reducing the degree of non-determinism of k-NN queries in NDDSs. The generalized form presented here enables the GEH distance to be used for a much greater variety of scenarios than was possible with the original form.     

A Contrary Opinion--and a Reassurance: Comment.

Comments on a note from Dr. Frederick C. Thorne appearing in the March issue of American Psychologist (1956, 11, 152), entitled "Psychologists, Heal Thyselves!" Thorne's note addressed the handling by the American Psychological Association of ethics cases involving individual members. Here, the current author takes exception to Thorne's characterization of the ethics review process as "moralistic, judgmental, and punitive rather than constructive, rehabilitative, and healing." The author, a member (and one-time chairman) of the Committee on Ethics of the APA (1938-40), attempts to contribute a better understanding of the services furnished by the Association's Committee on Scientific and Professional Ethics and Conduct. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New hihg-oleic peanut cultivars grown in the Southwestern United States

The chemical composition of five high-oleic peanut lines grown in Oklahoma was examined. Tamrun OL 01, Tamrun OL 02, TX 977164, and TX 977239 were developed using conventional breeding procedures. SunOleic and Tamrun 96 were the parent lines. These lines demonstrated outstanding agronomic characteristics in Oklahoma. The peanut seeds analyzed in this study contained 42 to 49% oil, 25 to 29% protein, 9 to 12% total dietary fiber, about 2% ash, and 5% moisture. The peanut seeds were rich in potassium. Phosphorus and calcium were the two other two major minerals present in all the samples. The proximate compositions of all the breeding lines were within the range of the parent lines except they had 80% (w/w) oleic acid, which was significantly higher than the parent lines. This study indicates that conventional genetic selection for high-oleic concentration does not cause substantial unintentional changes in peanut chemical compositions.     

Structural, optical and electronic properties of oxidized AIN thin films at different temperatures

We report on the properties of a novel insulator, AlO:N for application in semiconductors produced by thermally oxidizing AlN thin films. The process steps were similar to those used for SiO₂, creating the possibility of a new technology for metal-insulator-semiconductor field effect devices and integrated circuits. Thin films of AlN were deposited by radio-frequency magnetron reactive sputtering on p-type silicon or fused quartz substrates. As-deposited AlN film thickness ranged from 0.05 to 0.7 μm, with polycrystalline structure revealed by x-ray diffraction. Oxidation was performed under O₂ flow at 800 to 1100°C for 1–4 h. AlN films were oxidized partially or fully into Al₂O₃, depending on initial thickness, oxidation temperature and time. X-ray diffraction indicates the presence of several phases of Al₂O₃ at 1000°C, whereas at 1100°C, only the α-Al₂O₃ phase was found. Considering the importance of surface field effect device applications, the surfaces of oxidized films were examined with atomic force microscopy in air, and a clear change was observed in the surface structure of the oxidized film from that of as-deposited AlN films. Capacitance-voltage measurements of metal-oxide-semiconductor structures yielded a dielectric constant of AlO:N between 8–12 and a net oxide-trapped-charge density of ∼10¹¹ cm⁻². Using Fourier transform infrared spectrometry transmittance and reflectance, some α-Al₂O₃ modes were observed. In this paper, we describe the general properties of the oxide thin films, bulk and interface, at different temperatures.     

Triple-axis X-ray reciprocal space mapping of InyGa1−yAs thermophotovoltaic diodes grown on (1 0 0) InP substrates

Analysis of the composition, strain-relaxation, layer-tilt, and the crystalline quality of In_yGa_1−yAs/InP_1−xAs_x thermophotovoltaic (TPV) diodes grown by metal-organic vapor phase epitaxy (MOVPE) is demonstrated using triple-axis X-ray reciprocal space mapping techniques. In_0.53Ga_0.47As (E_gap=0.74 eV) n/p junction diodes are grown lattice matched (LM) to InP substrates and lattice-mismatched (LMM) In_0.67Ga_0.33As (E_gap=0.6 eV) TPV diodes are grown on three-step InP_1−xAs_x (0<x<0.32) buffer layers on InP substrates. X-ray reciprocal space maps about the symmetric (4 0 0) and asymmetric (5 3 3) reciprocal lattice points (RELPs) determine the in-plane and out-of-plane lattice parameters and strain of the In_yGa_1−yAs TPV active layer and underlying InP_1−xAs_x buffers. Triple-axis X-ray rocking curves about the LMM In_0.67Ga_0.33As RELP show an order of magnitude increase of its full-width at half-maximum (FWHM) compared to that from the LM In_0.53Ga_0.47As (250 vs. 30 arcsec). Despite the significant RELP broadening, the photovoltaic figure of merits show that the electronic quality of the LMM In_0.67Ga_0.33As approaches that of the LM diode material. This indicates that misfit-related crystalline imperfections are not dominating the photovoltaic response of the optimized LMM In_0.67Ga_0.33As material compared with the intrinsic recombination processes and/or recombination through native point defects, which would be present in both LMM and LM diode material. However, additional RELP broadening in non-optimized LMM In_0.67Ga_0.33As n/p junction diodes does correspond to significant degradation of TPV diode open-circuit voltage and minority carrier lifetime demonstrating that there is correlation between X-ray FWHM and the electronic performance of the LMM TPV diodes.     

On-farm Evaluation of Biological Nitrogen Fixation Potential and Grain Yield of Lablab and Two Soybean Varieties in the Northern Guinea Savanna of Nigeria

Several legumes with high biological nitrogen fixation (BNF) potentials have been studied in on-station trials. The processes involved in BNF and the benefits of these species to crop production need to be evaluated using farmers' management practices in farmers' fields. An on-farm trial with 20 farmers was conducted in the northern Guinea savanna (NGS) of Nigeria. The aims were to evaluate the BNF potentials of an improved soybean variety (TGx 1448-2E) and a local variety (Samsoy-2) when inoculated with Bradyrhizobium strains, and of Lablab in farmer-managed and researcher-managed soybean-maize and Lablab-maize crop rotation systems. The level of soil P was generally low with more than 50% of the fields having less than the critical P level. The plant available P content was statistically significantly (P = 0.05) correlated with P in grain (r = 0.60), P in the shoot (r = 0.68), grain yield (r = 0.40) and nodule weight (r = 0.35). Variations in plant parameters (nodulation, shoot dry matter, percentage nitrogen derived from the air [%Ndfa], grain yield, and nutrient uptake) among and within farmers’ fields were attributed to differences in soil fertility and crop management. About 60% of the fields were moderately fertile, sufficient to support legume establishment, while about 30% of the farmers' fields had a low fertility level. For farmers in the study area to benefit from the BNF potentials of the legumes, an external P fertilizer input was necessary as well as suitable crop management practices because all parameters measured in the researcher-managed plots were higher than in the farmer-managed plots.     

Current-voltage characteristics of high current density siliconEsaki diodes grown by molecular beam epitaxy and the influence ofthermal annealing

We present the characteristics of uniformly doped silicon Esaki tunnel diodes grown by low temperature molecular beam epitaxy (T_growth=275°C) using in situ boron and phosphorus doping. The effects of ex situ thermal annealing are presented for temperatures between 640 and 800°C. A maximum peak to valley current ratio (PVCR) of 1.47 was obtained at the optimum annealing temperature of 680°C for 1 min. Peak and valley (excess) currents decreased more than two orders of magnitude as annealing temperatures and times were increased with rates empirically determined to have thermal activation energies of 2.2 and 2.4 eV respectively. The decrease in current density is attributed to widening of the tunneling barrier due to the diffusion of phosphorus and boron. A peak current density of 47 kA/cm² (PVCR=1.3) was achieved and is the highest reported current density for a Si-based Esaki diode (grown by either epitaxy or by alloying). The temperature dependence of the current voltage characteristics of a Si Esaki diode in the range from 4.2 to 325 K indicated that both the peak current and the excess current are dominated by quantum mechanical tunneling rather than by recombination. The temperature dependence of the peak and valley currents is due to the band gap dependence of the tunneling probability