Diffusion and electrical properties of Boron and Arsenic doped poly-Si and poly-GexSi1−x(x 0.3)Ge_xSi_1-x(x~0.3) as gate material for sub-0.25 µm complementary metal oxide semiconductor applications

In this paper the texture, morphology, diffusion and electrical (de‐) activation of dopants in polycrystalline GexSi1-x and Si have been studied in detail. For gate doping B+,BF2+ and As+ were used and thermal budgets were chosen to be compatible with deep submicron CMOS processes. Diffusion of dopants is different for GeSi alloys, B diffuses significantly more slowly and As has a much faster diffusion in GeSi. For B doped samples both electrical activation and mobility are higher compared to poly‐Si. Also for the first time, BF2+ data of doped layers are presented, these show the same trend as the B doped samples but with an overall higher sheet resistance. For arsenic doping, activation and mobility are lower compared to poly‐Si, resulting in a higher sheet resistance. The dopant deactivation due to long low temperature steps after the final activation anneal is also found to be quite different. Boron‐doped GeSi samples show considerable reduced deactivation whereas arsenic shows a higher deactivation rate. The electrical properties are interpreted in terms of different grain size, quality and properties of the grain boundaries, defects, dopant clustering, and segregation, and the solid solubility of the dopants

Proof of the volume conjecture for Whitehead chains

We prove the volume conjecture for an infinite family of links called Whitehead chains that generalizes both the Whitehead link and the Borromean rings.Comment: 11 pages, 1 figure. See also http://www.science.uva.nl/~riveen/papers.html New in version two is a computation for the constant term in the asymptotic expansion. The proof of lemma 5 has been omitted because it is almost the same as that of lemma

Interface engineering for organic electronics : manufacturing of hybrid inorganic-organic molecular crystal devices

Organic semiconductors are at the basis of Organic Electronics. Objective of this dissertation is “to fabricate high-quality organic molecular single-crystal devices”, to explore the intrinsic properties of organic semiconductors. To achieve this, the in situ fabrication of complete field-effect transistors by direct deposition of metal contacts and oxide gate\ud dielectrics on the surface of free-standing pentacene single-crystals at room temperature (with the ‘quasi-dynamic stencil deposition’ technique in pulsed laser deposition) is selected as main approach.\ud First, the structure of vapor-grown pentacene single-crystals is investigated. The observed morphology shows step flow is the dominant crystal growth mechanism. For pentacene, the most common oxidation product and largest impurity present is 6,13-pentacenequinone. It is observed that this quinone is preferentially located as a thin monolayer (partly) covering the crystal surface. In order to remove the quinones selectively, the partly-oxidized crystals are heated in vacuum at a fixed temperature overnight.\ud Next, the direct deposition of various materials through a stencil on the pentacene singlecrystal surface by PLD is investigated. By taking several precautions in the process, lowkinetic energy deposition or ‘soft-landing’ was achieved. Smooth and isolated patterns with a well-defined geometry were successfully deposited, without obvious destruction of the fragile substrate. The terraced structure of the underlying pentacene substrate is often still noticeable on top of the patterned features. A series of gold patterns is deposited on silicon oxide and pentacene single-crystals; the results show that the growth evolution of the surface roughness is similar on both kinds of substrates.\ud Finally, the influence of the deposition parameters applied in the device fabrication and performing a heat treatment on the electrical properties of pentacene single-crystals is investigated, by characterizing space-charge-limited current and field-effect transistor devices fabricated on the surface of pentacene single-crystals

Periodic solutions to a mean-field model for electrocortical activity

We consider a continuum model of electrical signals in the human cortex, which takes the form of a system of semilinear, hyperbolic partial differential equations for the inhibitory and excitatory membrane potentials and the synaptic inputs. The coupling of these components is represented by sigmoidal and quadratic nonlinearities. We consider these equations on a square domain with periodic boundary conditions, in the vicinity of the primary transition from a stable equilibrium to time-periodic motion through an equivariant Hopf bifurcation. We compute part of a family of standing wave solutions, emanating from this point.Comment: 9 pages, 5 figure