P. A. Childs

A one‐dimensional solution of the Boltzmann transport equation including electron–electron interactions

In this article a technique is described for solving the one‐dimensional spatially dependent Boltzmann transport equation with electron–electron interactions included in the scattering model. The analysis is illustrated by solving the Boltzmann transport equation over a potential profile typical of that found in the channel of a metal–oxide–semiconductor field‐effect transistor. A comparison is made between the distribution functions obtained when electron–electron interactions are included and excluded from the scattering model. It is found that electron–electron interactions significantly increase the electron population at energies greater than are available from the electric field.

Deposition of passivated gold nanoclusters onto prepatterned substrates

Gold nanoclusters, chemically passivated with decanethiol, have been deposited from solution onto silicon dioxide surfaces prepatterned by photolithography. After lift-off of the photoresist, preferential cluster accumulation is observed along the edges of the resist structures. Elsewhere on the hydrophilic surface, islands of clusters are observed. By contrast, HF treatment, creating a hydrophobic surface, leads to wetting of the unmasked regions of the substrate by the passivated clusters.

High-energy electron–electron interactions in silicon and their effect on hot carrier energy distributions

This paper presents results from the calculation of the high-energy electron–electron scattering rate in silicon based on a full energy-band structure obtained by the pseudopotential technique. The effects on the scattering rate of the overlap integrals, wave-vector-dependent dielectric function and umklapp processes are described and the transition rate is compared with that obtained using a semiclassical analysis based on a parabolic energy dispersion. A hybrid Monte Carlo/iterative technique for solving the Boltzmann transport equation is used to obtain the electron energy distribution function generated by binary particle interactions in a one-dimensional system.

On the above supply voltage hot carrier distribution in semiconductor devices

In this letter we show that contrary to recent suggestions the hot carrier distribution at energies greater than the maximum available from the electric fields within a device does not take the form exp(−e/kTL), where TL is the lattice temperature. The effective temperature is shown to be typically 1.35TL close to the supply energy, only approaching TL at energies well above that available from the electric field. Our results are obtained by solving the one‐dimensional Boltzmann transport equation using a novel hybrid Monte Carlo/iterative technique.

Spatially transient hot electron distributions in silicon determined from the chambers path integral solution of the Boltzmann transport equation

Abstract A new technique is presented for determining the spatially transient hot electron distribution function in silicon. The Boltzmann transport equation is solved deterministically using a modificationm of the Chambers path integral solution. This formulation is shown to be relatively simple to implement, retains all essential physics and avoids the use of Legendre polynomial expansions. The accuracy of the technique is confirmed by comparison with Monte Carlo simulations. This method is computationally very efficient and should find applications in the study of hot carrier effects in silicon.

Modeling charge transport in graphene nanoribbons and carbon nanotubes using a Schrödinger-Poisson solver

Interest in carbon-based electronics has been stimulated in recent years, initially through the discovery of carbon nanotubes, but recently with the formation of graphene layers. In this paper metal-oxide-semiconductor (MOS) systems based on these carbon structures are used to model and compare charge transport within them. Schrodinger’s equation is solved self-consistently with Poisson’s equation, using the scattering matrix method. A tight-binding model is used to determine the energy band structure in graphene. The current-voltage characteristics of MOS devices based on graphene and those based on carbon nanotubes demonstrate significant differences associated with their respective transmission probabilities.

ANALYTIC EXPRESSIONS FOR IMPACT IONIZATION RATES AND SECONDARY PARTICLE ENERGY DISTRIBUTIONS IN SEMICONDUCTORS

Analytic expressions are obtained for the energy dependent impact ionization rate and secondary particle energy distribution functions in semiconductors based on the random-k technique. By approximating the conduction and valence band structure by a simple parabolic energy dispersion the impact ionization rate in semiconductors is found to have the form ∝(E−ET)7/2. The analytic expressions obtained for the secondary particle energy distribution functions are found to give excellent agreement with results obtained from a rigorous full band structure analysis for the case of silicon. By extending the model to multiple parabolic bands which emulate the true density of states a good agreement with results obtained on the basis of the full band structure is obtained for a range of semiconductor materials.

Time and real space dependence of impact ionization events in low noise impact avalanche transit time diodes

Impact avalanche transit time (IMPATT) diodes are an important source of radio-frequency power at millimeter and submillimeter wavelengths. However, exploitation of these devices has been restricted, as they are commonly believed to suffer from high noise levels. In this article, we demonstrate that a heterostructure IMPATT diode has the potential for almost noise-free operation. Our analysis is based on a Monte Carlo simulation of oscillating IMPATT devices.

Design and fabrication of colloid-based vertical nanoscale devices

The design and fabrication of a vertical nanodevice with an active region based on gold colloidal nanoparticles deposited on a silicon nanopillar is presented. Devices are fabricated in parallel using natural lithography to create an array of silicon pillars. The nanoscale volume of the active region results from the combination of silicon pillar technology coupled with well controlled vertical processing. The results in this paper show the fabrication procedure at each stage, leading to a structure designed to demonstrate proof of principal of our approach.

Bragg scattering of x-rays in multiwalled carbon nanotubes

In the past few years it has been shown theoretically that carbon nanotubes coated with various materials have the potential to act as waveguides at x-ray frequencies. At these frequencies the angle of incidence relative to the axis of the nanotube is a few milliradians, creating significant challenges for the experimental confirmation of mode formation. Recent developments in the growth of multiwalled carbon nanotubes with WS2 walls suggest that they have the potential to act as Bragg fibers at x-ray frequencies. In this paper we use the scattering matrix method to study mode formation in multiwalled carbon nanotubes coated with gold. It is found that they are capable of acting as Bragg fibers but the wall thickness and the number of bilayers must be increased in order to obtain mode confinement.