Onset Of Inversion Research Articles

2D and 3D TCAD simulation of III-V channel FETs at the end of scaling

Quantum drift diffusion corrections, models for the one- and two-dimensional density of states, a non-local model for source-to-drain tunneling, and a simple ballistic mobility model are jointly used to simulate IDVGS-characteristics of scaled III-V-channel nFETs. The sub-threshold swing of double-gate ultra-thin-body and gate-all-around nanowire geometries are extracted for different gate lengths, and the semi-classical results are compared with those from the quantum transport simulator QTx. The low-dimensional density of states in combination with the ballistic mobility yields an overall good agreement with the QTx transfer curves after the onset of inversion and decreases ION by two orders of magnitude in comparison to the simulation with a large diffusive mobility. It is shown that source-to-drain tunneling sets a limit to scaling at a gate length of about 10nm due to the degradation of the sub-threshold swing. Simulating this effect with a low-dimensional density of states reveals inconsistencies. They are attributed to the tunneling model, which had been derived for a three-dimensional electron gas.

Conduction Threshold in Accumulation-Mode InGaZnO Thin Film Transistors.

The onset of inversion in the metal-oxide-semiconductor field-effect transistor (MOSFET) takes place when the surface potential is approximately twice the bulk potential. In contrast, the conduction threshold in accumulation mode transistors, such as the oxide thin film transistor (TFT), has remained ambiguous in view of the complex density of states distribution in the mobility gap. This paper quantitatively describes the conduction threshold of accumulation-mode InGaZnO TFTs as the transition of the Fermi level from deep to tail states, which can be defined as the juxtaposition of linear and exponential dependencies of the accumulated carrier density on energy. Indeed, this permits direct extraction and visualization of the threshold voltage in terms of the second derivative of the drain current with respect to gate voltage.

A Model for Lubrication by Oil-in-Water Emulsions

A model for oil-in-water emulsion has been developed in this paper. A group of viscosity coefficients transiting smoothly and incessantly from the thick film region to the thin film region is defined. The contributions from disperse and continuous phases to the total lubricant pressure and pressure gradient are functions of the oil concentration and the film thickness. The parameters used in these functions are determined by a series of computational fluid dynamics simulations. The onset of inversion and the viscosity after inversion are also investigated. It is found that the critical volume fraction of oil in the inception of inversion is dependent on the oil viscosity and a factor regarding the combined effects from the emulsifier, pH value, droplet size, and the shear rate. A series of simulations using the proposed model has been carried out and compared with the experimental results, such as the film thickness and the extension of oil pool for various rolling speeds and supply oil concentrations. The numerical outputs are basically in agreement with the experiments.

Ultrafast Bimolecular Electron Transfer Dynamics in Micellar Media

Ultrafast photoinduced bimolecular electron transfer (ET) dynamics between 7-aminocoumarin derivatives and N,N-dimethylaniline (DMAN) has been studied in neutral (TX100), cationic (DTAB) and anionic (SDS) micellar media. A very fast decay time constant (tau(fast)) shorter than approximately 10 ps has been observed for the coumarins in the presence of DMAN in all of the three micellar media. In this time scale, reactants in the micellar phase undergo ET interactions without involving diffusion or reorientation of the reactants and thus can be envisaged as equivalent to nondiffusive bimolecular ET reaction. The fastest ET rates estimated as the inverse of the shortest lifetime components of the fluorescence decay (k(et) congruent with tau(fast)(-1)) nicely follow the predicted Marcus inversion behavior with reaction exergonicity (-DeltaG degrees), irrespective of the nature of micelles considered. Onset of inversion in ET rates occur at approximately 0.61 eV lower exergonicity in SDS and TX100 micelles compared with that in DTAB micelle and are rationalized following two-dimensional ET (2DET) theory. These differences suggest the possibility of tuning Marcus inversion by proper selection of micelles. Interestingly, ET rates (k'(et)) obtained from the conventional Stern-Volmer analysis of the relatively longer time constants of the fluorescence decays also exhibit similar Marcus correlation with DeltaG degrees, showing clear inversion behavior. Fitting of Marcus correlation curves for k(et) and k'(et) indicate two largely different values for the electronic coupling parameters. In micellar media, as the interacting donor-acceptor molecules are on an average expected to be separated by an intervening surfactant chain and the reorientation rate of the reactants is quite slow, it is predicted that the ultrafast ET (k(et)) component arises because of the surfactant separated donor-acceptor pairs that are orientated perfectly to give the maximum electronic coupling. The slower ET (k'(et)) is predicted to arise because of those pairs where the donor-acceptor orientations are not very suitable but good enough to give a sizable electronic coupling.

On-demand single-photon source using a nanoscale metal–insulator–semiconductorcapacitor

We propose an on-demand single-photon source for quantum cryptography using ametal–insulator–semiconductor quantum dot capacitor structure. The main component inthe semiconductor is a p-doped quantum well, and the cylindrical gate under considerationis only nanometres in diameter. As in conventional metal–insulator–semiconductorcapacitors, our system can also be biased into the inversion regime. However, due to thesmall gate area, at the onset of inversion there are only a few electrons residing in aquantum dot. In addition, because of the strong size quantization and large Coulombenergy, the number of electrons can be precisely controlled by the gate voltage. Afterholding just one electron in the inversion layer, the capacitor is quickly biased back to theflat-band condition, and the subsequent radiative recombination across the bandgapresults in single-photon emission. We present numerical simulation results of asemiconductor heterojunction and discuss the merits of this single-photon source.

Impact of the band–band tunneling in silicon on electrical characteristics of Al/SiO 2/p +-Si structures with the sub-3 nm oxide under positive bias

Measurements of current–voltage and capacitance–voltage characteristics were performed for metal––tunnel oxide––silicon structures on p +-silicon wafers doped to 2×10 18–2×10 19 cm −3. Obtained results show at least two striking points. First, the forward (metal “+”) current is amazingly high and comparable in value with the reverse-bias current (metal “−”). Second, capacitance–voltage curves exhibit a distortion in the depletion regime and a hump indicating the onset of inversion. The hump is accentuated with decreasing frequency. These features are suggested to appear due to a tunneling of the valence band electrons within the forbidden gap of silicon and further into metal. Eventually, such electrons may enter the conduction band of silicon where a fraction of them can be temporarily captured at the interface and impurity defects forming thereby an inversion layer.

Three-dimensional self-consistent simulation of silicon quantum-dot floating-gate flash memory device

We report on the simulation of single-electron charging operation of a silicon quantum-dot memory device using the self-consistent solutions of the Schrodinger and Poisson equations. We focus on the effects of the poly-wrapped gate on the onset of inversion. We show that the geometry of the control gate causes the inversion to occur on the vertical sides of the channel. The device experiences a strongly nonuniform threshold voltage shift as a function of the number of electrons in the dot to reach about 0.5 V when the floating gate quantum-dot is charged from empty to ten electrons.

Investigation of active media for a short-wave gas dynamic laser

The process of formation of an active medium on the visible and ultraviolet intervals in a recombining plasma flow through a supersonic nozzle has been investigated theoretically and experimentally. The conditions of onset of inversion over its interval of existence have been theoretically determined. A highly ionized xenon plasma, generated by a pulsed gas dynamic source of the “shock tube with nozzle” type, was used in the experiments. Amplification of the emission in the blue—green region of the spectrum was obtained for the 6p4D 5 2/° —6s4P3/2 (wavelength 0.5419 μm) and 6p'2P3/25d2D5/2(0.4973μm) transitions of the Xe II ion.

Sandbox experiments of inverted listric and planar fault systems

The kinematic and geometric evolution of basement-controlled inversion structures has been analyzed using a plane strain sandbox apparatus. The results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut-off angles of 60° to the horizontal, are described in detail. The hangingwall above these detachment geometries was constructed from alternate layers of sand and mica, in order to simulate an anisotropic sedimentary sequence. In both experiments, initial shortening at the onset of inversion was accommodated by bulk strain. This was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post-rift sequence at approximately the same angle as the upper part of the detachment fault (i.e. 60°). Reactivation of relatively steep, intra-basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15% contraction. This resulted in gently dipping thrusts that propagated upwards through the post-rift sequence to produce “harpoon” shaped structures. Later in the inversion phase, after approximately 15% contraction, backthrusts cut through and displaced the original antithetic extensional graben faults, producing downward tapering wedge-shaped structures at the margins of the basin. Although deformation in these experiments was limited to purely dip-slip displacement, the nature of the original extensional faults and their reactivated tip regions resulted in cross-sectional geometries that have a marked resemblance to strike-slip induced flower structures. Uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling-out point of the detachment in the case of the planar fault geometry. The results of these experiments show distinct similarities to structures seen on seismic sections form the southern North Sea and other inverted sedimentary basins.