Experimental Study on the Subthreshold Swing of Silicon Nanowire Transistors

SOI based wrap-gate silicon nanowire FETs are fabricated through electron beam lithography and wet etching. Dry thermal oxidation is used to further reduce the patterned fins cross section and transfer them into nanowires. Silicon nanowire FETs with different nanowire widths varying from 60 nm to 200 nm are fabricated and the number of the nanowires contained in a channel is also varied. The on-current (I-ON) and off-current (I-OFF) of the fabricated silicon nanowire FET are 0.59 mu A and 0.19 nA respectively. The subthreshold swing (SS) and the drain induced barrier lowering are 580 mV/dec and 149 mVN respectively due to the 30 nm thick gate oxide and 1015 cm(-3) lightly doped silicon nanowire channel. The nanowire width dependence of SS is shown and attributed to the fact that the side-gate parts of a wrap gate play a more effectual role as the nanowires in a channel get narrower. It seems the nanowire number in a channel has no effect on SS because the side-gate parts fill in the space between two adjacent nanowires.

Material effects on stress-induced defect generation in trenched silicon-on-insulator structures

We have investigated the influence of the material properties of the silicon device layer on the generation of defects, and in particular slip dislocations, in trenched and refilled fusion-bonded silicon-on-insulator structures. A strong dependence of the ease of slip generation on the type of dopant species was observed, with the samples falling into three basic categories; heavily boron-doped silicon showed ready slip generation, arsenic and antimony-doped material was fairly resistant to slip, while silicon moderately or lightly doped with phosphorous or boron gave intermediate behavior. The observed behavior appears to be controlled by differences in the dislocation generation mechanism rather than by dislocation mobility. The introduction of an implanted buried layer at the bonding interface was found to result in an increase in slip generation in the silicon, again with a variation according to the dopant species. Here, the greatest slip occurred for both boron and antimony-implanted samples. The weakening of the implanted material may be related to the presence of a band of precipitates observed in the silicon near the bonding interface. (C) 2001 The Electrochemical Society.

Concentrations of phosphates and silicon in near-bottom and interstitial waters of the Baltic Sea

Fine structure of vertical distributions of phosphorus and silicon in near-bottom layers and interstitial waters is studied in different regions of the Baltic Sea (Gulf of Finland, Bornholm area, Gotland trench). Data obtained are used to calculate fluxes of mineral forms of phosphorus and silicon in exchange processes between sediments and the near-bottom water layer. Depending on sediment types, values of nutrient fluxes vary from 9.8 to 632.6 µg-at/m**2/day for phosphorus and from 232.4 to 1881.1 µg-at/m**2/day for silicon. Fluxes calculated for different regions are compared.

Laser-fired contact optimization in c-Si solar cells

In this work we study the optimization of laser-fired contact (LFC) processing parameters, namely laser power and number of pulses, based on the electrical resistance measurement of an aluminum single LFC point. LFC process has been made through four passivation layers that are typically used in c-Si and mc-Si solar cell fabrication: thermally grown silicon oxide (SiO2), deposited phosphorus-doped amorphous silicon carbide (a-SiCx/H(n)), aluminum oxide (Al2O3) and silicon nitride (SiNx/H) films. Values for the LFC resistance normalized by the laser spot area in the range of 0.65–3 mΩ cm2 have been obtained

Nitrogen, phosphorus, silica, and carbon in Moreton Bay, Queensland, Australia: Differential limitation of phytoplankton biomass and production

Subtropical estuaries have received comparatively little attention in the study of nutrient loading and subsequent nutrient processing relative to temperate estuaries. Australian estuaries are particularly susceptible to increased nutrient loading and eutrophication, as 75% of the population resides within 200 km of the coastline. We assessed the factors potentially limiting both biomass and production in one Australian estuary, Moreton Bay, through stoichiometric comparisons of nitrogen (N), phosphorus (P), silicon (Si), and carbon (C) concentrations, particulate compositions, and rates of uptake. Samples were collected over 3 seasons in 1997-1998 at stations located throughout the bay system, including one riverine endmember site. Concentrations of all dissolved nutrients, as well as particulate nutrients and chlorophyll, declined 10-fold to 100-fold from the impacted western embayments to the eastern, more oceanic-influenced regions of the bay during all seasons. For all seasons and all regions, both the dissolved nutrients and particulate biomass yielded N : P ratios < 6 and N : Si ratios < 1. Both relationships suggest strong limitation of biomass by N throughout the bay. Limitation of rates of nutrient uptake and productivity were more complex. Low C : N and C : P uptake ratios at the riverine site suggested light limitation at all seasons, low N : P ratios suggested some degree of N limitation and high N : Si uptake ratios in austral winter suggested Si limitation of uptake during that season only. No evidence of P limitation of biomass or productivity was evident.

Electronic properties of homoepitaxial (111) highly boron-doped diamond films

The use of diamond as a semiconductor for the realization of transistor structures, which can operate at high temperatures (>700 K), is of increasing interest. In terms of bipolar devices, the growth of n-type phosphorus doped diamond is more efficient on the (111) growth plane; p-type boron-doped diamond growth has been most usually grown in the (100) direction and, hence, this study into the electronic properties, at high temperatures, of boron-doped diamond (111) homoepitaxial layers. It is shown that highly doped layers (hole carrier concentrations as high as 2×1020 cm-3) can be produced without promoting the onset of (unwanted) hopping conduction. The persistence of valance-band conduction in these films enables relatively high mobility values to be measured ( ~ 20 cm2/V?s) and, intriguingly, these values are not significantly reduced at high temperatures. The layers also display very low compensation levels, a fact that may explain the high mobility values since compensation is required for hopping conduction. The results are discussed in terms of the potential of these types of layers for use with high temperature compatible diamond transistors.

Templated i-PVD of metallic nanodot arrays

The results of numerical simulation of plasma-based, porous, template-assisted nanofabrication of Au nanodot arrays on highly-doped silicon taking into account typical electron density of low-temperature plasma of 1017-1018 m-3 and electron temperature of 2-5 eV are reported here. Three-dimensional microscopic topography of ion flux distribution over the outer and inner surfaces of the nanoporous template is obtained via numerical simulation of Au ion trajectories in the plasma sheath, in the close proximity of, and inside the nanopores. It is shown that, by manipulating the electron temperature, the cross-sheath potential drop, and by additionally altering the structure of the nanoporous template, one can control the ion fluxes within the nanopores, and eventually maximize the ion deposition onto the top surface of the developing crystalline Au nanodots (see top panel in the figure). In the same time, this procedure allows one to minimize amorphous deposits on the sidewalls that clutter and may eventually close the nanopores, thus disrupting the nanodot growth process, as it is shown in the bottom panel in the figure on the right.

X-ray and IR characterisation of Nasicon solid solution, Na1+xZr2SixP3−xO12

X-ray and IR studies on Nasicon solid solutions, Na1+xZr2SixP3−xO12, are carried out as a function of composition x. X-ray diffraction studies show that the unit cell volume increases as x increases and exhibits a maximum at x ≈ 2. On further increase in x the unit cell volume decreases. The infrared absorption peak positions and the splitting of these absorption peaks suggest a distortion of the PO4 and SiO4 tetrahedra. But the distortion is not large enough to change the local symmetry around the phosphorus or silicon ion from Td to C3v.

Low-Temperature Fluorination Of Some Nonmetals And Nonmetal Compounds With Fluorine

Low temperature fluorination with elemental fluorine of elemental phosphorus, sulphur, silicon, amorphous carbon and phosphorus trichloride, phosphorus pentoxide, triphenylphosphine, hexafluorodisilane, hexachlorodisilane, hexabromodisilane, tetrasulphur tetranitride, sulphur dioxide, thionyl chloride and sulphuryl chloride has been carried out in freon-11 medium. The corresponding fluoro compounds have been isolated in near quantitative yields, purified by low temperature fractional condensation and characterised by IR spectroscopy and elemental analysis.

Semi-insulating layer for novel high voltage polysilicon thin film transistors

This work describes the deposition and characterisation of semi-insulating oxygen-doped silicon films for the development of high voltage polycrystalline silicon (poly-Si) circuitry on glass. The performance of a novel poly-Si High Voltage Thin Film Transistor (HVTFT) structure, incorporating a layer of semi-insulating material, has been investigated using a two dimensional device simulator. The semi-insulating layer increases the operating voltage of the HVTFT structure by linearising the potential distribution in the device offset region. A glass compatible semi-insulating layer, suitable for HVTFT applications, has been deposited by the Plasma Enhanced Chemical Vapour Deposition (PECVD) technique from silane (SiH4), nitrous oxide (N2O) and helium (He) gas mixtures. The as-deposited films are furnace annealed at 600°C which is the maximum process temperature. By varying the N2O/SiH4 ratio the conductivity of the annealed films can be accurately controlled up to a maximum of around 10-7 Ω-1cm-1. Helium dilution of the reactant gases improves both film uniformity and reproducibility. Raman analysis shows the as-deposited and annealed films to be completely amorphous. A model for the microstructure of these Semi-Insulating Amorphous Oxygen-Doped Silicon (SIAOS) films is proposed to explain the observed physical and electrical properties.

Nutrient salts in the United Arab Emirates waters (the Arabian Gulf and the Gulf of Oman)

This paper deals with the levels and distributions of nutrient salts in the United Arab Emirates waters. Water samples were collected bimonthly during 1994-1995 from the marine environment of the United Arab Emirates, which extends more than 800km along the Arabian Gulf and the Gulf of Oman. Concentrations of ammonium, nitrite, nitrate, phosphate, silicate, as well as total concentrations of total dissolved nitrogen, phosphorus, and silicon in the area were scattered in the ranges: (ND-6.32; mean: 0.84 µg-at N/l), ND-3.02; mean: 0.42 µg-at N/l), (ND-10.88; mean: 1.18 µg-at N/1), (ND-4.22; mean: 0.62 µg-at P/l), (1.14-28.80; mean: 6.52 µg-at Si/l), (1.52-39.58; mean: 12.28 µg-at N/l), (0.40-4.98; mean: 1.07 µg-at P/l), and (2.77-44.74; mean: 13.02 Si/l) respectively. Of inorganic nitrogen species, ammonium was the highest in the Arabian Gulf waters and nitrate was the highest at the Gulf of Oman. The dissolved inorganic nitrogen total species, phosphate and silicate amounted to 16.4, 47.6, 56.5% respectively, of the concentrations of nitrogen, phosphorus and silicon in the Arabian Gulf and 22.6, 64.4, 44.9% respectively, in the Gulf of Oman, indicating that more than 80% of nitrogen was present in organic forms. Distributions of nutrient in the two regions were higher in the summer season and lower in the winter season due to the oxidation of organic materials. Regional distributions revealed higher values for nitrite (1.3 times), nitrate (2.8 times), phosphate (2.2 times), total dissolved nitrogen (1.3 times), total dissolved phosphorus (1.6 times), and total dissolved silicon (1.3 times) in the Gulf of Oman compared to the Arabian Gulf, indicating more oligotrophic conditions at the Arabian Gulf Whereas no distinct patterns of distribution were observed in the Arabian Gulf waters, an increase in the seaward direction was measured at the Gulf of Oman. Vertical distributions indicated a general increase with depth in the two regions. The mean ratios for total concentrations of phosphorus, nitrogen, and silicon in the Arabian Gulf (1: 11.6: 12.6) and the Gulf of Oman (1: 10.1: 11.8) were lower than the Redfield ratio.

Au@Si-n: Growth behavior, stability and electronic structure

The configurations, stability, and electronic structure of AuSin (n = 1-16) clusters have been investigated within the framework of the density functional theory at the B3PW91/LanL2DZ and PW91/DNP levels. The results show that the Au atom begins to occupy the interior site for cages as small as Si-11 and for Si-12 the Au atom completely falls into the interior site forming Au@Si-12 cage. A relatively large embedding energy and small HOMO-LUMO gap are also found for this Au@Si-12 structure indicating enhanced chemical activity and good electronic transfer properties. All these make Au@Si-12 attractive for cluster-assembled materials.