Comprehensive investigation of Ge-Si bonded interfaces using oxygen radical activation

In this work, we investigate the directly bonded germanium-silicon interfaces to facilitate the development of high quality germanium silicon hetero integration at the wafer scale. X-ray photoelectron spectroscopy data is presented which provides the chemical composition of the germanium surfaces as a function of the hydrophilic bonding reaction at the interface. The bonding process induced long range deformation is detected by synchrotron x-ray topography. The hetero-interface is characterized by measuring forward and reverse current, and by high resolution transmission electron microscopy. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3601355

Negative-bias-temperature-instability and hot carrier effects in nanowire junctionless p-channel multigate transistors

Negative-bias-temperature-instability (NBTI) and hot-carrier induced device degradation have been experimentally compared between accumulation mode (AM) p-channel multigate transistors (pMuGFETs) and junctionless (JL) pMuGFET. NBTI degradation is less significant in junctionless pMuGFETs than AM pMuGFETs. The threshold voltage shift is less significant in junctionless transistors than AM transistors. The device simulation shows that the peak of lateral electric field and the impact ionization rate of AM device are larger than those of junctionless devices. (C) 2012 American Institute of Physics. (doi:10.1063/1.3688245

All-Electrical Quantum Computation with Mobile Spin Qubits

We describe and discuss a solid state proposal for quantum computation with mobile spin qubits in one-dimensional systems, based on recent advances in spintronics. Static electric fields are used to implement a universal set of quantum gates, via the spin-orbit and exchange couplings. Initialization and measurement can be performed either by spin injection from/to ferromagnets, or by using spin filters and mesoscopic spin polarizing beam-splitters. The vulnerability of this proposal to various sources of error is estimated by numerical simulations. We also assess the suitability of various materials currently used in nanotechnology for an actual implementation of our model.Comment: 10 pages, 6 figs, RevTeX

Low-temperature conductance oscillations in junctionless nanowire transistors

Junctionless nanowire transistors show more marked oscillations conductance oscillations than inversion-mode devices. These oscillations can be observed at higher temperature, drain voltage, and gate voltage than in surface-channel, inversion-mode multigate metal-oxide-semiconductor field-effect devices. Clear oscillations are observed at 77 K at a drain voltage of 100 mV in devices with a 10 x 10 nm(2) cross section. (C) 2010 American Institute of Physics. (doi:10.1063/1.3506899

Improvement of carrier ballisticity in junctionless nanowire transistors

In this work we show that junctionless nanowire transistor (JNT) exhibits lower degree of ballisticity in subthreshold and higher ballisticity above threshold compare to conventional inversion-mode transistors, according to quantum mechanical simulations. The lower degradation of the ballisticity above threshold region gives the JNT near-ballistic transport performance and hence a high current drive. On the other hand, lower ballisticity in subthreshold region helps reducing the off-current and improves the subthreshold slope. A three-dimensional quantum mechanical device simulator based on the nonequilibrium Green's function formalism in the uncoupled mode-space approach has been developed to extract the physical parameters of the devices. (C) 2011 American Institute of Physics. (doi:10.1063/1.3559625

Rock-eating mycorrhizas: their role in plant nutrition and biogeochemical cycles

A decade ago, tunnels inside mineral grains were found that were likely formed by hyphae of ectomycorrhizal (EcM) fungi. This observation implied that EcM fungi can dissolve mineral grains. The observation raised several questions on the ecology of these ¿rock-eating¿ fungi. This review addresses the roles of these rock-eating EcM associations in plant nutrition, biogeochemical cycles and pedogenesis. Research approaches ranged from molecular to ecosystem level scales. Nutrient deficiencies change EcM seedling exudation patterns of organic anions and thus their potential to mobilise base cations from minerals. This response was fungal species-specific. Some EcM fungi accelerated mineral weathering. While mineral weathering could also increase the concentrations of phytotoxic aluminium in the soil solution, some EcM fungi increase Al tolerance through an enhanced exudation of oxalate. Through their contribution to Al transport, EcM hyphae could be agents in pedogenesis, especially podzolisation. A modelling study indicated that mineral tunnelling is less important than surface weathering by EcM fungi. With both processes taken together, the contribution of EcM fungi to weathering may be significant. In the field vertical niche differentiation of EcM fungi was shown for EcM root tips and extraradical mycelium. In the field EcM fungi and tunnel densities were correlated. Our results support a role of rock-eating EcM fungi in plant nutrition and biogeochemical cycles. EcM fungal species-specific differences indicate the need for further research with regard to this variation in functional traits

Characterization of a junctionless diode

A diode has been realised using a silicon junctionless (JL) transistor. The device contains neither PN junction nor Schottky junction. The device is measured at different temperatures. The characteristics of the JL diode are essentially identical to those of a regular PN junction diode. The JL diode has an on/off current ratio of 10(8), an ideality factor of 1.09, and a reverse leakage current of 1 x 10(-14) A at room temperature. The mechanism of the leakage current is discussed using the activation energy (E-A). The turn-on voltage of the device can be tuned by JL transistor threshold voltage. (C) 2011 American Institute of Physics. (doi: 10.1063/1.3608150

Simulation of junctionless Si nanowire transistors with 3 nm gate length

Inspired by recent experimental realizations and theoretical simulations of thin silicon nanowire-based devices, we perform proof-of-concept simulations of junctionless gated Si nanowire transistors. Based on first-principles, our primary predictions are that Si-based transistors are physically possible without major changes in design philosophy at scales of similar to 1 nm wire diameter and similar to 3 nm gate length, and that the junctionless transistor avoids potentially serious difficulties affecting junctioned channels at these length scales. We also present investigations into atomic-level design factors such as dopant positioning and concentration. (C) 2010 American Institute of Physics. (doi:10.1063/1.3478012

Field-effect mobility extraction in nanowire field-effect transistors by combination of transfer characteristics and random telegraph noise measurements

A technique based on the combined measurements of random telegraph-signal noise amplitude and drain current vs. gate voltage characteristics is proposed to extract the channel mobility in inversion-mode and accumulation-mode nanowire transistors. This method does not require the preliminary knowledge of the gate oxide capacitance or that of the channel width. The method accounts for the presence of parasitic source and drain resistance effect. It has been used to extract the zero-field mobility and the field mobility reduction factor in inversion-mode and junctionless transistors operating in accumulation mode. (C) 2011 American Institute of Physics. (doi:10.1063/1.3626038

A nanomechanical resonator shuttling single electrons at radio frequencies

We observe transport of electrons through a metallic island on the tip of a nanomechanical pendulum. The resulting tunneling current shows distinct features corresponding to the discrete mechanical eigenfrequencies of the pendulum. We report on measurements covering the temperature range from 300 K down to 4.2 K. We explain the I-V curve, which differs from previous theoretical predictions, with model calculations based on a Master equation approach.Comment: 5 pages, 4 jpeg-figure