The effect of dielectric mismatch on excitons and trions in cylindrical semiconductor nanowires

We investigated the energy levels of excitons (X) and trions (X ^±) in free-standing nanowires with strong lateral carrier confinement. Within the adiabatic approximation the two (resp. three) particle problem reduces to an effective one (resp. two) dimensional Schrödinger equation for the relative motion which is solved numerically. Dielectric mismatch effects are taken into account that result in a distorted Coulomb interaction between the charged particles. We obtain the X and X ^± binding energies as function of the dielectric mismatch ratio. To obtain these energies, we constructed tractable analytical expressions for the effective potential in the wire which significantly reduces the amount of computational time.     

Calculation of phonon spectrum and thermal properties in suspended 〈100〉 In X Ga1?X As nanowires

The phonon spectra in zinc blende InAs, GaAs and their ternary alloy nanowires (NWs) are computed using an enhanced valence force field (EVFF) model. The physical and thermal properties of these nanowires such as sound velocity, elastic constants, specific heat (C _v ), phonon density of states, phonon modes, and the ballistic thermal conductance are explored. The calculated transverse and longitudinal sound velocities in these NWs are ∼25% and 20% smaller compared to the bulk velocities, respectively. The C _v for NWs are about twice as large as the bulk values due to higher surface to volume ratio (SVR) and strong phonon confinement in the nanostructures. The temperature dependent C _v for InAs and GaAs nanowires show a cross-over at 180°K due to higher phonon density in InAs nanowires at lower temperatures. With the phonon spectra and Landauer’s model the ballistic thermal conductance is reported for these III–V NWs. The results in this work demonstrate the potential to engineer the thermal behavior of III–V NWs.     

Role of inelastic electron–phonon scattering in electron transport through ultra-scaled amorphous phase change material nanostructures

The electron transport through ultra-scaled amorphous phase change material (PCM) GeTe is investigated by using ab initio molecular dynamics, density functional theory, and non-equilibrium Green’s function, and the inelastic electron–phonon scattering is accounted for by using the Born approximation. It is shown that, in ultra-scaled PCM device with 6 nm channel length, \(<\) 4 % of the energy carried by the incident electrons from the source is transferred to the atomic lattice before reaching the drain, indicating that the electron transport is largely elastic. Our simulation results show that the inelastic electron–phonon scattering, which plays an important role to excite trapped electrons in bulk PCM devices, exerts very limited influence on the current density value and the shape of current–voltage curve of ultra-scaled PCM devices. The analysis reveals that the Poole–Frenkel law and the Ohm’s law, which are the governing physical mechanisms of the bulk PCM devices, cease to be valid in the ultra-scaled PCM devices.     

Lead-free Bi-based complex perovskite nanowires: Sol?Cgel-hydrothermal processing and the densification behavior

One dimensional ferroelectric nanostructure is noteworthy for their size-dependent dielectric, piezoelectric, and electro-optic properties with corresponding applications in smart devices such as transducers, actuators, and high-k dielectrics at the nanoscale. Due to their extremely small size and anisotropy, the control of nucleation and growth of one dimensional nanostructure materials is still a big challenge. Sol?Cgel-hydrothermal chemistry combines both the merits of sol?Cgel and hydrothermal technique, which offers a very useful tool for low-temperature synthesis of the ferroelectric nanowires. In this paper, we will review recent works devoted to the synthesis of Bi-based complex perovskite nanowires, i.e. Na_0.5Bi_0.5TiO₃, K_0.5Bi_0.5TiO₃, (K_0.5Bi_0.5)_0.4Ba_0.6TiO₃ and (Na_0.8 K_0.2)_0.5Bi_0.5TiO₃ systems. We will focus on the formation mechanism and morphology evolution of nanowires prepared in sol?Cgel-hydrothermal process. Moreover, due to the good sinterability of the nanowires, the high-densified single-phase ceramic can be fabricated even by a conventional sintering process.     

Spontaneous and stimulated electron–photon interactions in nanoscale plasmonic near fields

The interplay between free electrons, light, and matter offers unique prospects for space, time, and energy resolved optical material characterization, structur...     

Ambipolar leakage suppression in electron–hole bilayer TFET: investigation and analysis

In this paper, we propose and simulate two new structures of electron–hole bilayer tunnel field-effect transistors (EHBTFET). The proposed devices are n-heterogate with \(\hbox {M}_{1}\) as overlap gate, \(\hbox {M}_{2}\) as underlap gate and employs a high-k dielectric pocket in the drain underlap. Proposed structure 1 employs symmetric underlaps (Lgs = Lgd = Lu). The leakage analysis of this structure shows that the lateral ambipolar leakage between channel and drain is reduced by approximately three orders, the OFF-state leakage is reduced by one order, and the \(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\) ratio is increased by more than one order at \(V_\mathrm{{GS}}=V_{\mathrm{DS}} =1.0\) V as compared to the conventional Si EHBTFET. The performance is improved further by employing asymmetric underlaps (\(\hbox {Lgs}\ne \hbox {Lgd}\)) with double dielectric pockets at source and drain, called as proposed structure 2. The pocket dimensions have been optimized, and an average subthreshold swing of 17.7 mV/dec (25.5% improved) over five decades of current is achieved with an ON current of \(0.23~\upmu \hbox {A}/\upmu \hbox {m}\) (11% improved) in proposed structure 2 in comparison with the conventional EHBTFET. Further, the parasitic leakage paths between overlap/underlap interfaces are blocked and the OFF-state leakage is reduced by more than two orders. A high \(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\,\hbox {ratio}~>10^{9}\) (two orders higher) is achieved at \(V_{\mathrm{DS}} =V_{\mathrm{GS}} =1.0~\hbox {V}\) in the proposed structure 2 in comparison with the conventional one.     

Stochastic simulation of bimolecular reactions in vicinity of traps and applications to electron–hole recombination in 2D and 3D inhomogeneous semiconductors

Stochastic models and simulation algorithms for spatially separated reactants in the vicinity of traps were developed. The methods were applied to simulate electron–hole recombination in inhomogeneous semiconductors. Continuous kinetic Monte Carlo methods were compared with a discrete cellular automata algorithm. Recombination kinetics for pure diffusion and diffusion in the vicinity of tunneling regimes were investigated. A difference in the electron–hole spatial correlations simulated by the discrete and continuous models and the relevant segregation phenomena in two-dimensional (2D) and three-dimensional (3D) semiconductors was discovered. This results in different spatial patterns during segregation of electron and hole clusters. Comparative analysis of different statistical characteristics evaluated by the two studied methods was performed. In addition, the execution time of codes implementing the two models was studied versus the number of electron–hole pairs simulated and the size of the semiconductor domain.     

Elastic interaction between 90° domain walls and misfit dislocations in epitaxial ferroelectric thin films

Abstract

The elastic interaction between 90° domain walls and misfit dislocations in epitaxial ferroelectric thin films is studied theoretically for the first time. The interaction energy is evaluated via the calculation of a work done by the dislocation stress field during the development of spontaneous strains in a polydomain film. For a single wall separating c and a domains, the energy and force of the interaction with individual misfit dislocations and periodic dislocation arrays are computed as a function of the wall position in a film. The results obtained are used to describe the pinning of 90° walls by misfit dislocations in epitaxial films. The critical electric field E_c , which is necessary for the motion of domain walls through the potential relief created by misfit dislocations, is evaluated and compared with the observed coercive fields of ferroelectric thin films.     

Microglia modulation with 1070-nm light attenuates Aβ burden and cognitive impairment in Alzheimer's disease mouse model

Photobiomodulation, by utilizing low-power light in the visible and near-infrared spectra to trigger biological responses in cells and tissues, has been conside...     

Is selectivity achieved in critical low-voltage UPS and standbygenerator power circuits?

This paper reviews typical critical low-voltage uninterruptible power supply (UPS) systems and standby generator power circuits used in the petrochemical industry to determine if selectivity is achieved between protective devices during short-circuit conditions. Alternate system configurations are proposed when complete selectivity is not achieved. Generator excitation systems and UPS support during fault conditions is discussed     

Exceptional women? Gender and technology in U.K. higher education

It is now commonplace to say that technology is more readily associated with boys and men than with girls and women. In popular representations, even where girls are ostensibly included, they tend to be presented as “other” to technology or their relationship to technology is trivialized. “Real technology” the message seems to be, is not for women and girls. The author reflects on research she has carried out over the last 10-15 years (to 1999) and, in particular, two projects which examined women's experiences in technological courses in UK tertiary education in the mid 1980s and the early 1990s. What struck her in her reflections was the extraordinary similarity in some central themes in both projects. In particular, the author reflects upon the prevalence of very limited, and therefore limiting, understandings of the gender-technology relationship within conventional technology curricula and the possibility for challenging the understandings that are offered by more progressive and innovative curricula in information technology based education     

Windows of opportunity? Schools and the Internet in the U.K

For many with an interest in education, and certainly for the governments of most industrialized nations, connecting schools to the Internet is the number one priority for investment. Typical levels of connectivity for schools at present involve one or two networked computers, introduced at a fairly negligible cost, with a similarly minimal effect on education provision. What is envisaged goes much further than this, with whole classrooms wired up to virtually unlimited Internet access throughout the school. If all of this is to be achieved, it means a huge investment. In the United Kingdom, as elsewhere, the government acknowledges this, and says it intends to get the private sector to put up much of the funding. However, if that money is to be found (whether from public or private sources), then when should it be spent? Whether the industry money will be forthcoming is questionable, given past experience, and it may well be that the provision of information and communications technologies (ICTs) continues to develop only slowly from the rather minimal level that now exists. Nevertheless, the author questions the setting of priorities, rather than considering what may or may not actually happen. The call for Internet connection is an attempt to find a simple technical solution to a complex social problem, and the urgency of the demand reveals a number of assumptions about the purpose of education and the social function of technology. Such questions are easily overlooked given the temptation to seize upon any possibility of additional funding for education     

Quantum transport of holes in 1D, 2D, and 3D devices: the?k?p?method

Quantum transport of holes in one-, two- and three-dimensional devices is simulated based on the 6-band k?p method. Detailed numerical aspects for an efficient development of a k?p-based simulator are provided. In particular, real-space and k-space discretization schemes for devices of different dimensionality are described and their effectiveness in numerical implementation is compared. The mode-space approach for drastic reduction of computation time is also described. The capability of the?k?p-based simulator is demonstrated by investigating various aspects of hole transport in devices of different dimensionality.