Near-thermal limit gating in heavily-doped III-V semiconductor nanowires using polymer electrolytes

Doping is a common route to reducing nanowire transistor on-resistance but has limits. High doping level gives significant loss in gate performance and ultimately complete gate failure. We show that electrolyte gating remains effective even when the Be doping in our GaAs nanowires is so high that traditional metal-oxide gates fail. In this regime we obtain a combination of sub-threshold swing and contact resistance that surpasses the best existing p-type nanowire MOSFETs. Our sub-threshold swing of 75 mV/dec is within 25% of the room-temperature thermal limit and comparable with n-InP and n-GaAs nanowire MOSFETs. Our results open a new path to extending the performance and application of nanowire transistors, and motivate further work on improved solid electrolytes for nanoscale device applications.Comment: 6 pages, 2 figures, supplementary available at journa

Boundary conditions and Berry phase in magnetic nanostructures

The effect of micromagnetic boundary conditions on the Berry curvature and topological Hall effect in granular nanostructures is investi- gated by model calculations. Both free surfaces and grain boundaries between interacting particles or grains affect the spin structure. The Dzyaloshinskii-Moriya interactions yield corrections to the Erdmann-Weierstrass boundary conditions, but the Berry curvature remains an exclusive functional of the local spin structure, which greatly simplifies the treatment of nanostructures. An explicit example is a model nanostructure with cylindrical symmetry whose spin structure is described by Bessel function and which yields a mean-field-type Hall-effect contribution that can be related to magnetic-force-microscopy images

Towards low-dimensional hole systems in Be-doped GaAs nanowires

GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly-confined 0D and 1D hole systems with strong spin-orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately-doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowly-doped nanowires and inability to reach a clear off-state under gating for the highly-doped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio ~$10^{4}$, and sub-threshold slope 50 mV/dec at T = 4 K. Lastly, we made a device featuring a moderately-doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantization highlighting the potential for future quantum device studies in this material system

The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors

We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs nanowire transistors in several atmospheres: air, dry pure N$_2$ and O$_2$, and N$_2$ bubbled through liquid H$_2$O and alcohols to identify whether phase-related structural/surface differences affect their response. Both WZ and ZB give poor gate characteristics in dry state. Adsorption of polar species reduces off-current by 2-3 orders of magnitude, increases on-off ratio and significantly reduces sub-threshold slope. The key difference is the greater sensitivity of WZ to low adsorbate level. We attribute this to facet structure and its influence on the separation between conduction electrons and surface adsorption sites. We highlight the important role adsorbed species play in nanowire device characterisation. WZ is commonly thought superior to ZB in InAs nanowire transistors. We show this is an artefact of the moderate humidity found in ambient laboratory conditions: WZ and ZB perform equally poorly in the dry gas limit yet equally well in the wet gas limit. We also highlight the vital role density-lowering disorder has in improving gate characteristics, be it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase nanowires.Comment: Accepted for publication in Nanotechnolog

p-GaAs nanowire MESFETs with near-thermal limit gating

Difficulties in obtaining high-performance p-type transistors and gate insulator charge-trapping effects present two major challenges for III-V complementary metal-oxide semiconductor (CMOS) electronics. We report a p-GaAs nanowire metal-semiconductor field-effect transistor (MESFET) that eliminates the need for a gate insulator by exploiting the Schottky barrier at the metal-GaAs interface. Our device beats the best-performing p-GaSb nanowire metal-oxide-semiconductor field effect transistor (MOSFET), giving a typical sub-threshold swing of 62 mV/dec, within 4% of the thermal limit, on-off ratio $\sim 10^{5}$, on-resistance ~700 k$\Omega$, contact resistance ~30 k$\Omega$, peak transconductance 1.2 $\mu$S/$\mu$m and high-fidelity ac operation at frequencies up to 10 kHz. The device consists of a GaAs nanowire with an undoped core and heavily Be-doped shell. We carefully etch back the nanowire at the gate locations to obtain Schottky-barrier insulated gates whilst leaving the doped shell intact at the contacts to obtain low contact resistance. Our device opens a path to all-GaAs nanowire MESFET complementary circuits with simplified fabrication and improved performance

Testing statistical bounds on entanglement using quantum chaos

Previous results indicate that while chaos can lead to substantial entropy production, thereby maximizing dynamical entanglement, this still falls short of maximality. Random Matrix Theory (RMT) modeling of composite quantum systems, investigated recently, entails an universal distribution of the eigenvalues of the reduced density matrices. We demonstrate that these distributions are realized in quantized chaotic systems by using a model of two coupled and kicked tops. We derive an explicit statistical universal bound on entanglement, that is also valid for the case of unequal dimensionality of the Hilbert spaces involved, and show that this describes well the bounds observed using composite quantized chaotic systems such as coupled tops.Comment: 5 pages, 3 figures, to appear in PRL. New title. Revised abstract and some changes in the body of the pape

Business process modelling and visualisation to support e-government decision making: Business/IS alignment

© 2017 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/978-3-319-57487-5_4.Alignment between business and information systems plays a vital role in the formation of dependent relationships between different departments in a government organization and the process of alignment can be improved by developing an information system (IS) according to the stakeholders’ expectations. However, establishing strong alignment in the context of the eGovernment environment can be difficult. It is widely accepted that business processes in the government environment plays a pivotal role in capturing the details of IS requirements. This paper presents a method of business process modelling through UML which can help to visualise and capture the IS requirements for the system development. A series of UML models have been developed and discussed. A case study on patient visits to a healthcare clinic in the context of eGovernment has been used to validate the models

Genetic local search for multicast routing with pre-processing by logarithmic simulated annealing

Over the past few years, several local search algorithms have been proposed for various problems related to multicast routing in the off-line mode. We describe a population-based search algorithm for cost minimisation of multicast routing. The algorithm utilises the partially mixed crossover operation (PMX) under the elitist model: for each element of the current population, the local search is based upon the results of a landscape analysis that is executed only once in a pre-processing step; the best solution found so far is always part of the population. The aim of the landscape analysis is to estimate the depth of the deepest local minima in the landscape generated by the routing tasks and the objective function. The analysis employs simulated annealing with a logarithmic cooling schedule (logarithmic simulated annealing—LSA). The local search then performs alternating sequences of descending and ascending steps for each individual of the population, where the length of a sequence with uniform direction is controlled by the estimated value of the maximum depth of local minima. We present results from computational experiments on three different routing tasks, and we provide experimental evidence that our genetic local search procedure that combines LSA and PMX performs better than algorithms using either LSA or PMX only

Phytochemical analysis of selected medicinal plants

Four medicinal plants including Ranunculus arvensis, Equisetum ravens, Carathamus lanatus and Fagonia critica were used for the study. All the plants were biologically active and were used for different types of ailments. Keeping in view their importance, this work was carried out to investigate the quantitative determination of their crude phytochemicals, vitamins and protein contents. The quantitative determination of crude phytochemicals (alkaloids, total phenols, flavonoids and saponins) vitamins (riboflavin, vitamin C, niacin and pectin) and protein were determined in the aforementioned herbs. The phytochemicals including alkaloids, total phenols, flavonoids and saponins were determined quantitatively using literature methods. Vitamins were measured using a UV/ visible spectrophotometer (UV- 1601 Shamidzu) and the protein was determined by the Micro KJeldahl’s method (Horwitz et al., 2000). The studied plants showed variable amounts of phytochemicals, vitamins and protein contents. The study is very important, in that it intended to show the contents of the studied medicinal herbs and also provide a scientific data base line which is of particular importance for the local practioners as well as for the local people using these herbs for a variety of body disorders.Key word: Phytochemical analysis, medicinal plants, Pakistan

Design and evaluation of a biologically-inspired cloud elasticity framework

The elasticity in cloud is essential to the effective management of computational resources as it enables readjustment at runtime to meet application demands. Over the years, researchers and practitioners have proposed many auto-scaling solutions using versatile techniques ranging from simple if-then-else based rules to sophisticated optimisation, control theory and machine learning based methods. However, despite an extensive range of existing elasticity research, the aim of implementing an efficient scaling technique that satisfies the actual demands is still a challenge to achieve. The existing methods suffer from issues like: (1) the lack of adaptability and static scaling behaviour whilst considering completely fixed approaches; (2) the burden of additional computational overhead, the inability to cope with the sudden changes in the workload behaviour and the preference of adaptability over reliability at runtime whilst considering the fully dynamic approaches; and (3) the lack of considering uncertainty aspects while designing auto-scaling solutions. In this paper, we aim to address these issues using a holistic biologically-inspired feedback switch controller. This method utilises multiple controllers and a switching mechanism, implemented using fuzzy system, that realises the selection of suitable controller at runtime. The fuzzy system also facilitates the design of qualitative elasticity rules. Furthermore, to improve the possibility of avoiding the oscillatory behaviour (a problem commonly associated with switch methodologies), this paper integrates a biologically-inspired computational model of action selection. Lastly, we identify seven different kinds of real workload patterns and utilise them to evaluate the performance of the proposed method against the state-of-the-art approaches. The obtained computational results demonstrate that the proposed method results in achieving better performance without incurring any additional cost in comparison to the state-of-the-art approaches