Design considerations for high performance avalanche photodiodemultiplication layers

We have studied the effect of the thickness of the multiplication region on the noise performance characteristics of avalanche photodiodes (APD's). Our simulation results are based on a full band Monte Carlo model with anisotropic threshold energies for impact ionization. Simulation results suggest that the well known McIntyre expression for the excess noise factor is not directly applicable for devices with a very thin multiplication region. Since the number of ionization events is drastically reduced when the multiplication layer is very thin, the “ionization coefficient” is not a good physical parameter to characterize the process. Instead “effective quantum yield,” which is a measure of the total electron-hole pair generation in the device, is a more appropriate parameter to consider. We also show that for the device structure considered here, modeling the excess noise factor using a “discrete Bernoulli trial” model as opposed to the conventional “continuum theory” produces closer agreement to experimental measurements. Our results reinforce the understanding that impact ionization is a strong function of carrier energy and the use of simplified field-dependent models to characterize this high energy process fails to accurately model this phenomenon     

Experimental determination of electron and hole mobilities in MOSaccumulation layers

This letter presents for the first time, the experimentally determined majority carrier mobilities in the accumulation layer of a MOSFET for both p-type and n-type channel doping for a wide range of doping concentrations. The measured carrier mobility is observed to follow a universal behavior at high transverse fields, similar to that observed for minority carriers in MOS inversion layers. At the higher doping levels, the effective mobility for majority carriers at low to moderate transverse fields is found to be very close to the bulk mobility. This is believed to be due to carrier screening of the ionized impurity scattering which dominates at the higher doping concentrations     

Parametric study on smoothed particle hydrodynamics for accurate determination of drag coefficient for a circular cylinder

Simulations of two-dimensional (2D) flow past a circular cylinder with the smoothed particle hydrodynamics (SPH) method were conducted in order to accurately determine the drag coefficient. The fluid was modeled as a viscous liquid with weak compressibility. Boundary conditions, such as a no-slip solid wall, inflow and outflow, and periodic boundaries, were employed to resemble the physical problem. A sensitivity analysis, which has been rarely addressed in previous studies, was conducted on several SPH parameters. Hence, the effects of distinct parameters, such as the kernel choices and the domain dimensions, were investigated with the goal of obtaining highly accurate results. A range of Reynolds numbers (1–500) was simulated, and the results were compared with existing experimental data. It was observed that the domain dimensions and the resolution of SPH particles, in comparison to the obstacle size, affected the obtained drag coefficient significantly. Other parameters, such as the background pressure, influenced the transient condition, but did not influence the steady state at which the drag coefficient was determined.     

Numerical aspects of a Godunov-type stabilization scheme for the Boltzmann transport equation

Journal of Computational Electronics - We discuss the numerical aspects of the Boltzmann transport equation (BE) for electrons in semiconductor devices, which is stabilized by Godunov’s...     

Wave propagation in functionally graded nanocomposites reinforced with carbon nanotubes based on second-order shear deformation theory

In the present article, as a first endeavor, the wave propagation in functionally graded nanocomposites reinforced with carbon nanotubes is investigated on the basis of second-order shear deformation theory. Four different types of functionally graded nanocomposites are presented. An analytical method is used to find the circular frequencies and phase velocities. To show the accuracy of the present methodology, our results for the free vibration are compared with the results of functionally graded plates available in the literature. The influences of different parameters are also investigated on the circular frequencies and phase velocities.     

CuIns2/Cus Nanocomposite: Synthesis via Simple Microwave Approach and Investigation Its Behavior in Solar Cell

CuInS₂/CuS nanocomposite were synthesized by a copper complex, [bis(ethylenediamine)copper(ΙΙ)] sulfate. Eight sulfur sources were used for this experiment. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis spectroscopy, and room temperature photoluminescence spectroscopy. Thin film of nanocomposite powder was fabricated and its feature (V_oc, J_sc and FF) was calculated by current–voltage (I–V) curve.     

The relative performance of alternative oxygen carriers for liquid chemical looping combustion and gasification

The relative performance of different potential liquid oxygen carriers within a novel system that can be configured for either chemical looping gasification or combustion is assessed. The parameters considered here are the melting temperature, the Gibbs free energy, reaction enthalpy, exergy and energy flows, syngas quality and temperature difference between the two reactors. Results show that lead, copper and antimony oxides are meritorious candidates for the proposed systems. Antimony oxide was found to offer strong potential for high quality syngas production because it has a reasonable oxygen mass ratio for gasification. A sufficiently low operating temperature to be compatible with concentrated solar thermal energy and a propensity to generate methane. In contrast, copper and lead oxides offer greater potential for liquid chemical looping combustion because they have higher oxygen mass ratio and a higher operating temperature, which enables better efficiency from a power plant. For all three metal oxides, the production of methane via the undesirable methanation reaction is less than 2% of the product gasses for all operating temperatures and an order of magnitude lower for lead.     

Effect of plate-like glass fillers on the mechanical properties of dental nanocomposites

In this study, glass flakes were incorporated into the spherical nanosilica component of the dental composites and its effect on the mechanical properties of these composites was investigated. To achieve a good interfacial adhesion between matrix resin and fillers, the particles were surface treated with a silane coupling agent (γ-MPS). Composites with different plate-like and spherical nanoparticle contents were prepared and their mechanical properties, including flexural strength, flexural modulus and fracture toughness were measured. The morphology of the particles and fracture surface of the composites were studied by SEM. The distribution of the flakes in the composite was also monitored using EDXA. Statistical analysis of the data was performed with ANOVA and the Tukey’s post hoc test was at a significance level of 0.05. The results showed that the flexural modulus and fracture toughness of specimens were improved with increasing the glass flake content up to 15 vol % which then declined upon further increase due to the stacking of the flakes on each other. A good interfacial adhesion was observed between matrix resin and particles in the SEM micrographs. The results of this study suggest that incorporation of glass flakes into the dental composites containing spherical nanosilica particles may enhance their mechanical properties.     

A critical review of bioceramics for magnetic hyperthermia

Magnetic hyperthermia (HT) using biocompatible ceramics is a ground-breaking, competent, and safe thermo-therapeutic strategy for cancer treatment. The magnetic properties of bioceramics, along with their structure and synthesis parameters, are responsible for the controlled heating of malignant tumors and are the key to clinical success. After providing a brief overview of magnetism and its significance in biomedicine, this review deals with materials selection and synthesis methods of bioceramics/glasses used for HT. Relevant research carried out on promising bioceramics for magnetic HT, with a focus on their size, shape, surface functionalization, magnetic field parameters, and in vitro/in vivo properties to optimize cancer therapy, is also discussed. Recent progress in magnetic HT combined with chemotherapy and phototherapy is especially highlighted, with the aim to provide interdisciplinary knowledge to advance further the applications of bioceramics in this field.