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Nesher G Vilan A Cohen H Cahen D Amy F Chan C Hwang J Kahn A 《The journal of physical chemistry. B》2006,110(29):14363-14371
A series of p- and n-GaAs-S-C(n)H(2n+1) || Hg junctions are prepared, and the electronic transport through them is measured. From current-voltage measurements, we find that, for n-GaAs, transport occurs by both thermionic emission and tunneling, with the former dominating at low forward bias and the latter dominating at higher forward bias. For p-GaAs, tunneling dominates at all bias voltages. By combining the analysis of the transport data with results from direct and inverse photoemission spectroscopy, we deduce an energy band diagram of the system, including the tunnel barrier and, with this barrier and within the Simmons tunneling model, extract an effective mass value of 1.5-1.6m(e) for the electronic carriers that cross the junctions. We find that transport is well-described by lowest unoccupied and highest occupied states at 1.3-1.4 eV above and 2.0-2.2 eV below the Fermi level. At the same time, the photoemission data indicate that there are continua of states from the conduction band minimum and the valence band maximum, the density of which varies with energy. On the basis of our results, it appears likely that, for both types of junctions, electrons are the main carrier type, although holes may contribute significantly to the transport in the p-GaAs system. 相似文献
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For over 27 years, SCD has been manufacturing and developing a wide range of high performance infrared detectors, designed
to operate in either the mid-wave (MWIR) or the long-wave (LWIR) atmospheric windows. These detectors have been integrated
successfully into many different types of system including missile seekers, time delay integration scanning systems, hand-held
cameras, missile warning systems and many others. SCD’s technology for the MWIR wavelength range is based on its well established
2D arrays of InSb photodiodes. The arrays are flip-chip bonded to SCD’s analogue or digital signal processors, all of which
have been designed in-house. The 2D focal plane array (FPA) detectors have a format of 320×256 elements for a 30-μm pitch
and 480×384 or 640×512 elements for a 20-μm pitch. Typical operating temperatures are around 77–85 K. Five years ago SCD began
to develop a new generation of MWIR detectors based on the epitaxial growth of antimonide based compound semiconductors (ABCS).
This ABCS technology allows band-gap engineering of the detection material which enables higher operating temperatures and
multi-spectral detection. This year SCD presented its first prototype FPA from this program, an InAlSb based detector operating
at a temperature of 100 K. By the end of this year SCD will introduce the first prototype MWIR detector with a 640×512 element
format and a pitch of 15 μm. For the LWIR wavelength range SCD manufactures both linear Hg1−xCdxTe (MCT) detectors with a line of 250 elements and time delay and integration (TDI) detectors with formats of 288×4 and 480×6.
Recently, SCD has demonstrated its first prototype uncooled detector which is based on VOx technology and which has a format of 384×288 elements, a pitch of 25 μm, and a typical NETD of 50 mK at F/1. In this paper,
we describe the present technologies and products of SCD and the future evolution of our detectors for the MWIR and LWIR detection.
The paper presented there appears in Infrared Photoelectronics, edited by Antoni Rogalski, Eustace L. Dereniak, Fiodor F. Sizov, Proc. SPIE Vol. 5957, 59570S (2005). 相似文献
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Amy F Chan CK Zhao W Hyung J Ono M Sueyoshi T Kera S Nesher G Salomon A Segev L Seitz O Shpaisman H Schöll A Haeming M Böcking T Cahen D Kronik L Ueno N Umbach E Kahn A 《The journal of physical chemistry. B》2006,110(43):21826-21832
Monolayers of alkyl chains, attached through direct Si-C bonds to Si(111), via phosphonates to GaAs(100) surfaces, or deposited as alkyl-silane monolayers on SiO2, are investigated by ultraviolet and inverse photoemission spectroscopy and X-ray absorption spectroscopy. Exposure to ultraviolet radiation from a He discharge lamp, or to a beam of energetic electrons, leads to significant damage, presumably associated with radiation- or electron-induced H-abstraction leading to carbon-carbon double-bond formation in the alkyl monolayer. The damage results in an overall distortion of the valence spectrum, in the appearance of (occupied) states above the highest occupied molecular orbital of the alkyl molecule, and in a characteristic (unoccupied state) pi resonance at the edge of the carbon absorption peak. These distortions present a serious challenge for the interpretation of the electronic structure of the monolayer system. We show that extrapolation to zero damage at short exposure times eliminates extrinsic features and allows a meaningful extraction of the density of state of the pristine monolayer from spectroscopy measurements. 相似文献
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Ilana Arnon Pearla Nesher Renata Nirenburg 《International Journal of Computers for Mathematical Learning》2001,6(2):167-214
The concept of equivalence class plays a significant role in the structure of Rational Numbers. Piaget taught that in order
to help elementary school children develop mathematical concepts, concrete objects and concrete reflection-enhancing-activities
are needed. The “Shemesh” software was specially designed for learning equivalence-classes of fractions. The software offers
concrete representations of such classes, as well as activities which cannot be constructed without a computer. In a discrete
Cartesian system students construct points on the grid and learn to identify each such point as a fraction-numeral (a denominator-numerator
pair). The children then learn to construct sets of such points, all of which are located on a line through the origin point.
They learn to identify the line with the set of its constituent equivalent fractions. Subsequently, they investigate other
phenomena and constructions in such systems, developing these constructions into additional fraction concepts. These concrete
constructions can be used in solving traditional fraction problems as well as in broadening the scope of fraction meaning.
Fifth-graders who used “Shemesh” in their learning activities were clinically interviewed several months after the learning
sessions ended. These interviews revealed evidence indicating initial actual development of the desired mathematical concepts.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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