Silicon Quantum Wires Research Articles

Consideration of electronic mean heat transport via a low dimension system

The object of research is the complex realm of energy localization and coherent ballistic electronic transport within low-dimensional silicon quantum wires, specifically those doped with germanium atoms. Unlike their three-dimensional counterparts, low-dimensional systems exhibit unique electronic transport behaviors, necessitating novel analytical approaches for a comprehensive understanding. The core of this investigation leverages the Phase Field Matching Theory (PMFT) and the tight-binding (TB) approximation, sophisticated methodologies that enable a deep dive into the quantum mechanical nuances of these systems. Through this lens, we examine the intricate dynamics of dispersion relationships, phase factors, group velocities, and notably, the impact of defects introduced by the germanium doping. This research meticulously analyzes how these defects affect electronic and thermal conductivities, along with densities of states, offering new insights into the role of Fano resonances in the fluctuation of transmission and reflection spectra. These resonances, we find, are crucially dependent on the nature of the defects, their configuration, and the electronic parameters in their vicinity, underscoring the nuanced interplay between material composition and electronic properties in low-dimensional systems. The implications of our findings extend far beyond the theoretical. They pave the way for significant advancements in nanotechnology and the design of electronic devices, highlighting the potential for creating more efficient, high-performance components. Furthermore, this work proposes a framework for developing non-destructive testing methodologies that could revolutionize material science by enabling the precise analysis of defects in low-dimensional systems without causing damage. This is particularly critical for the ongoing development of materials with optimized properties for various applications, from electronics to energy storage. In essence, this research not only enriches our understanding of the physics governing low-dimensional systems but also offers practical insights into leveraging these properties for technological innovation. By bridging the gap between theoretical physics and material science, our study sets the stage for the next generation of electronic components and non-destructive evaluation techniques, marking a significant step forward in the application of quantum mechanics to real-world challenges.

Local equilibrium and off-equilibrium phenomena in silicon quantum wires

Charge transport phenomena can been tackled in silicon quantum wires using a subband hydrodynamic model. This has been formulated by closing the moment system derived from the Schodinger-Poisson-Boltzmann equations on the basis of the Maximum Entropy Principle. The model can be used to deal with thermoelectric effects in Local equilibrium and off-equilibrium regimes.

(Gordon E. Moore Medal for Outstanding Achievement in Solid State Science and Technology Award Address) Towards Silicon-Based Photonic Integrated Circuits: The Quest for Compatible Light Sources

Optoelectronics and photonics are playing an essential role in many aspects of daily life, including information and communication technologies, environmental and green technologies, mechanical and chemical sensing, consumer electronics, and biomedicine. So far, the use of optical components in communication systems has been mainly limited to direct replacement of electrical cables by optical cables. With the continual increase in link bit rates, optical cables are now replacing electrical cables for shorter and shorter interconnect lengths. Optoelectronic and photonic technologies are becoming less costly and more integrated, and there is currently an opportunity for optics to move “inside the box” and change the interconnect topology at all levels. Optical interconnects are required these days for on-chip technology as an alternative to metal wires, because of data transmission bottlenecks introduced by their unavoidable delay times, significant signal degradation, problems with power dissipation, and electromagnetic interference. Such optical interconnects will help in extending the life of Moore’s Law [1]. Currently, most optoelectronic devices are fabricated as discrete components. This approach is based on serial (e.g., step-by-step) fabrication and packaging, and it makes optoelectronic technology drastically different compared to microelectronics, where the domination of parallel fabrication made possible ultra large scale integration. Also, discrete assembly reduces the optoelectronic system reliability and decreases the manufacturing yield. Additional complications arise due to materials issues: in microelectronics the major material is elemental silicon, while traditional semiconductor materials for optoelectronics are III-V compound alloys with much more complex technological requirements. Finally, optical waveguides and waveguide based devices are very bulky compared to electron devices; thus, the densities of electron devices in integrated circuits are many orders of magnitude greater compared to that in integrated optoelectronic systems. Silicon photonics, where photonics devices are fabricated by using silicon or silicon compatible materials and where the manufacturing is based on the available microelectronics infrastructure, is emerging as the technology that can face all these challenges [2]. Silicon photonics is booming and growing at an incredible pace with many breakthroughs appearing day by day [3,4]. Speed, integration density, active components, logic, nonlinear optics, etc., are all surpassed frontiers, which silicon photonics has continuously moved apart. Many devices enabled by silicon photonics are already on the market and new ones are emerging continually [5]. Despite these advances, the major deficiency in such optoelectronic and photonic devices remains the lack of suitable silicon-based light emitters and especially lasers, which would enable a fully integrated silicon platform. In order to be commercially viable, these light emitters need to be efficient, fast, operational at room temperature, and, perhaps most importantly, be compatible with mainstream CMOS technology. Another important requirement is in the emission wavelength, which should match the optical waveguide low-loss spectral region of 1.3–1.6 μm. The main problem in utilizing silicon as a light emitter is its indirect electronic band gap that results in inefficient carrier recombination and a long radiative lifetime. Many quite different approaches to alleviating the miserable light emission in bulk silicon (~10-4 quantum efficiency at 300 K) have been proposed and are actively being explored [6]. Some, such as Si1-xGex quantum well or Si/SiO2 superlattice structures, rely on band structure engineering, while others rely on quantum confinement effects in lower dimensional structures, as typified by silicon quantum dots or porous silicon. Still another approach is impurity-mediated luminescence from, for example, isoelectronic substitution or by the addition of rare earth or transition metal ions to silicon. In this presentation, the use of the quantum confinement approach we have employed to producing efficient light emission in silicon and germanium will be reviewed. Nanostructured systems that will be covered include porous silicon, silicon quantum wells and wires, super unit cells, and arrays of silicon-germanium quantum dots. https://en.wikipedia.org/wiki/Moore%27s_lawL. Pavesi and D.J. Lockwood, Silicon Photonics (Springer, Berlin, 2004).Special issue on Silicon Photonics, Proc. IEEE 97(7), July (2009).D.J. Lockwood and L. Pavesi, Silicon Photonics II: Components and Integration (Springer, Berlin, 2011).L. Pavesi and D.J. Lockwood, Silicon Photonics III: Systems and Applications (Springer, Berlin, 2016).D.J. Lockwood, Light Emission in Silicon (Academic, New York, 1998).

Scaling issues of Schottky junction solar cells based on graphene and silicon quantum wires in the sub-10-nm regime

In this paper, a scaling study of heterojunction solar cells based on p-type silicon quantum wires with rectangular cross sections in the sub-10-nm regime and graphene (p-SiQWs/G) is presented. The scaling issues in p-SiQWs/G solar cells performance focusing on SiQWs diameter, the distance between SiQWs, and the number of graphene layers is investigated by a coupled optical and electrical model taking into account the quantum effects of SiQWs. A minimum efficiency of p-SiQWs/G solar cells is obtained for SiQWs with moderate diameter. The p-SiQWs/G solar cell with small diameter shows high efficiency because of wide band gap of SiQWs with small diameter. On the other hand, p-SiQWs/G solar cell with large diameter also shows high efficiency because of strong light absorption of SiQWs resulted from high surface area. The results also show that the denser packing of SiQWs and monolayer graphene improve the efficiency of p-SiQWs/G solar cells.

Hydrodynamic modeling of electron transport in silicon quantum wires

An extended hydrodynamic model self-consistently coupled to the 2D Schrödinger and 3D Poisson equations is introduced, to describe charge transport in Silicon Nanowires. It is been formulated by taking the moments of the multisubband Boltzmann equation, and the closure relations for the fluxes and production terms have been obtained by means of the Maximum Entropy Principle. The low-field mobility for a Gate-All-Around in a SiNW transistor has been evaluated.

Thermodynamics of annealing of nanoporous silicon

The thermodynamic calculation of melting of the surface layer of nanoporous silicon quantum wires is performed and the results obtained are compared with the Monte Carlo calculation data. Approximations made under the assumption that nanopores are filled due to the pore surface energy variation made it possible to explain the formation of cavities as dependent on pore depth and width.

Thermoelectric effects in silicon quantum wires

Thermoelectric effects have been tackled in silicon quantum wires using a subband hydrodynamic model. This has been formulated by closing the moment system derived from the Schroedinger-Poisson-Boltzmann equations on the basis of the maximum entropy principle. Under the hypothesis of Local Thermal Equilibrium, the thermoelectric coefficients have been determined without any fitting procedure.

Hydrodynamic modeling of silicon quantum wires

A hydrodynamic model for silicon quantum wires is formulated by taking the moments of the multisubband Boltzmann equation, coupled to the Schrodinger-Poisson system. Explicit closure relations for the fluxes and production terms (i.e. the moments on the collisional operator) are obtained by means of the Maximum Entropy Principle of Extended Thermodynamics, including scattering of electrons with acoustic and non-polar optical phonons. By using this model, thermoelectric effects are investigated.

Intraband photon absorption in edge-defined nanowire superlattices for optoelectronic applications

We calculate the conduction miniband energy dispersion relation in an edge-defined silicon quantum wire periodic nanostructure embedded in SiO2. Our main aim is to predict the behavior of these nanostructures when used as components in optoelectronic devices such as, for example, photodetectors or intermediate-band solar cells. We take into consideration the effects of nonparabolicity and anisotropy and the different electron states arising from each valley when solving the Schrödinger equation. From these results, we investigate the intraband photon absorption coefficient for those transitions between minibands arising from the conduction band. We analyze the influence of light polarization and level of doping of the system in order to ascertain the best conditions for operation.

ELECTRON TRANSPORT IN SILICON QUANTUM WIRE DEVICES

The simulation of the electron transport in silicon devices is usually based on a coupling of the semiclassical Boltzmann transport equation with the Poisson equation. We follow this successful approach and extend it with the effective mass Schrödinger equation leading to a Schrödinger–Poisson–Boltzmann system for the description of the electron transport in silicon quantum wire devices. Phonon-scattering is taken into account by phonon distributions in thermal equilibrium. In addition, we study the nonsteady state behavior of the electron transport in the considered device.

A method for performing fully quantum mechanical simulations of gated silicon quantum wire structures

As transistors get smaller, fully quantum mechanical treatments are required to properly simulate them. Most quantum approaches treat the transport as ballistic, ignoring the scattering that is known to occur in such devices. Here, we review the method we have developed for performing fully quantum mechanical simulations of nanowire transistor devices which incorporates scattering through a real-space self-energy, starting with the assumption that the interactions are weak. The method we have developed is applied to investigate the ballistic to diffusive crossover in a silicon nanowire transistor device.

A nonparabolicity model compared to tight-binding: The case of square silicon quantum wires

This work presents a nonparabolicity (NP) model which is able to improve the effective mass approximation (EMA) for computing transfer characteristics of square silicon quantum wire transistors (SQWT) working in the ballistic regime and subjected to bandstructure effects. The model is found to be treatable within the same transport framework as used in a present 3D EMA Poisson–Schrödinger solver thus keeping a comparable time efficiency. A full-band tight-binding (TB) code provides the bandstructures as well as the transfer characteristics related to a series of SQWTs needed for calibrating the NP model. In comparison with the EMA, the threshold voltage ( V T ) obtained via the NP model is notably closer to the TB data for all wire widths considered in this work. In addition, the NP model is found to satisfactorily predict the increase of the conduction masses belonging to the unprimed conduction valleys of the TB bandstructure.

Simulation of non-equilibrium electron transport in silicon quantum wires

The Simulation of the non-equilibrium behavior of the charge transport in semiconductor devices is usually based on a coupling of the semiclassical Boltzmann transport equation with the Poisson equation. We follow this successful approach but extend it with the Schrodinger effective mass equation leading to a Schrodinger-Poisson-Boltzmann system for the description of the non-equilibrium electron transport in silicon quantum wires. The silicon quantum wire is joined with a substrate, so that the phonons are non-confined. We take into account zero- and first order intra- and intervalley scattering mechanisms.

Simulation of a triple-gate single electron FET memory with a quantum dot floating gate and a quantum wire channel

This paper investigates a triple-gate single electron FET memory with a Si quantum dot floating gate and a Si quantum wire channel by establishing a numerical model of two-dimensional Schrdinger and Poisson equations. The electron concentration in the silicon quantum wire channel of different scales is investigated under conditions that diverse gate voltage and programming voltage are applied with a two-dimensional finite element solution. The influence of the quantum confinement effect and the electron distribution in the nano-scale channel on the structure is also investigated. Results of the simulation show that, the threshold voltage increases when the size of the channel decreases, and the voltage also increases as the number of electrons on the floating gate increases. However, a non-linear saturation tendency occurs when the number of injected electrons increases further, due to the high density of carriers in the nanoscale Si nanowire channel. Further research shows that the strong quantum confinement effect in the channel can effectively restrain the saturation tendency when the size of the channel is small enough. It's worth mentioning that the threshold voltage shift reflects the number of electrons stored on the floating gate.This effect implies a possibility of multi-level storage.

Calculated optical transitions in a silicon quantum wire modulated by a quantum dot

The photoluminescence lifetimes of Si quantum wires and dots have been previously calculated within a continuum model that takes into account the anisotropy of silicon band structure. Here, we present our calculations on the optical transitions in Si quantum wires modulated by a quantum dot. The geometrical parameters of the buldged wire are appropriate for porous Si and the ground state is localized. The photoluminescence lifetimes are calculated and compared with those of straight wires and dots. The magnitude of the lifetime is sensitive to the structural parameters of the nanostructures. Lifetimes varying from nanoseconds to milliseconds have been obtained. The results of the calculations provide insight to the optical properties of Si nanostructures.

Fractional form of “0.7 anomaly” in 1D hole systems

We analyze the fractional quantization of the ballistic conductance associated with the light and heavy holes bands in silicon quantum wires. It is shown that the formation of the localized hole state in the region of the quantum point contact connecting two quasi-1D hole leads modifies drastically the conductance pattern. Exchange interaction between localized and propagating holes results in the fractional quantization of the ballistic conductance different from those in electron systems. The value of the conductance at the additional plateaux depends on the offset between the bands of the light and heavy holes, Δ, and the sign of the exchange interaction constant.

Vibrational states in low-dimensional structures: An application to silicon quantum wires

The Raman scattering in Si nanowires is studied by means of the local bond-polarization model based on the displacement–displacement Green's function within the linear response theory. In this study, the Born potential, including central and non-central interatomic forces, and a supercell model are used. The results show a notable shift of the main Raman peak towards lower energies, in comparison with the bulk crystalline Si case. This shift is compared with the experimental data and discussed within the quantum confinement framework.

Silicon quantum wires on Ag(1 1 0): Fermi surface and quantum well states

One-dimensional Si quantum wires have been grown on silver single crystals upon deposition of ∼0.25 monolayer of Si on Ag(1 1 0) surfaces. Scanning tunneling microscopy (STM) clearly shows parallel 1D Si chains along the [−1 1 0] Ag crystallographic direction. Low Energy Electron Diffraction (LEED) confirms the massively parallel assembly of these selforganized Nanowires (NWs). We have characterized these nano-objects by measuring the dispersion of the NWs valence band at room temperature using Angle-Resolved PhotoEmission Spectroscopy (ARPES). Also, the Fermi Surface (FS) of the Ag(1 1 0) substrate has been mapped before and after the silicon deposition, trying to put in evidence the metallic or semiconductor character of the NWs silicon's states close to the Fermi level. Our results show the existence of well-defined quantum states associated to the silicon super-structure. Both LEED and ARUPS results confirm that the NWs have typical 1D features, however their metallic or semiconductor character could not be confirmed.

EnergyDispersion Relations for Holes in Silicon Quantum Wells and Quantum Wires

We calculate the energy dispersion relations in Si quantum wells (QW), E(k2D), and quantum wires (QWR), E(k1D), focusing on the regions with negative effective mass (NEM) in the valence band. The existence of such NEM regions is a necessary condition for the current oscillations in ballistic quasineutral plasma in semiconductor structures. The frequency range of such oscillations can be extended to the terahertz region by scaling down the length of structures. Our analysis shows that silicon is a promising material for prospective NEM-based terahertz wave generators. We also found that comparing to Si QWRs, Si QWs are preferable structures for NEM-based generation in the terahertz range.

Weak noncovalent Si···FC interactions stabilized fluoroalkylated rod‐like polysilanes as ultrasensitive chemosensors

AbstractNoncovalent interactions, such as hydrogen bonding, metal coordination, and π‐π stacking, are increasingly being utilized to develop well‐ordered and self‐organized supramolecular materials. Recently, new types of nonclassical weak interactions, such as CH···π, CH···FC, and CH···O, have been exploited in stabilizing the specific conformations of molecules and molecular assemblies in the solid state. These noncovalent interactions play an important role in materials comprised of polymer chains, because cooperative effects from a large number of weak interactions can lead to drastic changes in its conformation, several properties, and functionalities. The programmed design of synthetic helical polymer with well‐defined molecular conformation has been the main subject in modern polymer science and engineering. Silicon‐catenated polysilane is an ideal helical silicon quantum wire and polymers with unique photophysical properties. The present review highlights the spectroscopic evidences for through‐space weak Si···FC interaction in poly(methyl‐3,3,3‐trifluoropropylsilane) (1) in noncoordinating and coordinating solvents by means of NMR (29Si and 19F) and IR spectroscopies, and viscometric measurement. It was found that 1 is applicable for chemosensors with an extremely high sensitivity and selectivity toward fluoride ions in tetrahydrofuran (THF) and with high sensitivity for nitroaromatic compounds, detected by a decrease in the photoluminescence intensity in THF and in thin solid film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5060–5075, 2006