Transition matrix approach for Monte Carlo simulation of coupled electron/phonon/photon dynamics

A new approach for simulating the dynamics of electrons, phonons, and photons is described. The technique provides a Monte Carlo simulation of particle dynamics without the statistical noise associated with direct Monte Carlo simulation, treats physical phenomena with a wide range of time scales, and has a good computational efficiency. A transition matrix is first precomputed by direct Monte Carlo simulation. Particle populations are then updated at regular time steps by simple matrix multiplication while correcting for nonlinear effects such as carrier–carrier scattering, band filling, hot phonons, etc. The technique is well suited to studies of quantum well laser devices and pump-probe experiments where direct Monte Carlo simulation is exceedingly difficult

Self‐consistent scattering matrix calculation of the distribution function in semiconductor devices

The scattering matrix approach is a new technique for solving the Boltzmann equation in devices. We report a self-consistent application of the technique to realistic silicon devices exhibiting strong nonlocal effects. Simulation of a hot-electron, n-i-n diode demonstrates that the new technique efficiently and accurately reproduces Monte Carlo results without the statistical noise, allowing much tighter convergence with Poisson’s equation

Compact Models and the Physics of Nanoscale FETs

The device physics of nanoscale MOSFETs is reviewed and related to traditional compact models. Beginning with the Virtual Source model, a model for nanoscale MOSFETs expressed in traditional form, we show how a Landauer approach gives a clear, physical interpretation to the parameters in the model. The analysis shows that transport in the channel is limited by diffusion near the virtual source both below and above threshold, that current saturation is determined by velocity saturation near the source, not by the maximum velocity in the channel, and that the channel resistance approaches a finite value as the channel length approaches zero. These results help explain why traditional models continue to work well at the nanoscale, even though carrier transport is distinctly different from that at the microscale, and they identify the essential physics that physics-based compact models for nanoscale MOSFETs should comprehend

No Really, We Can Help with This: Librarians Facilitating Research Assignment Design

Premises: Students need scaffolded, authentic opportunities to practice and develop research skills. Interdisciplinary faculty collaboration on assignment redesign facilitates peer feedback that isn\u27t usually available. Bringing librarians to the assignment design table establishes stronger connections with and among teaching faculty and promotes deeper learning opportunities for students. Key principles: Reflect on where students get stuck. Make the implicit explicit. Scaffold the research process. Offer formative assessment and opportunities for peer learning. Consider authentic, renewable, or public-facing end products

A Spectral Flux Method for Solving the Boltzmann Equation

A spectral method for solving the Boltzmann equation by the scattering matrix approach is presented, The algorithm discussed can be used to simulate both bulk and device properties with arbitrary field profiles. Although the primary goal is to reduce the data storage problem of the scattering matrix approach, many of the concepts and mathematical properties developed may be useful for other traditional spectral methods as well

Enhancement of thermoelectric properties by energy filtering: Theoretical potential and experimental reality in nanostructured ZnSb

Energy filtering has been suggested by many authors as a means to improve thermoelectric properties. The idea is to filter away low-energy charge carriers in order to increase Seebeck coefficient without compromising electronic conductivity. This concept was investigated in the present paper for a specific material (ZnSb) by a combination of first-principles atomic-scale calculations, Boltzmann transport theory, and experimental studies of the same system. The potential of filtering in this material was first quantified, and it was as an example found that the power factor could be enhanced by an order of magnitude when the filter barrier height was 0.5~eV. Measured values of the Hall carrier concentration in bulk ZnSb were then used to calibrate the transport calculations, and nanostructured ZnSb with average grain size around 70~nm was processed to achieve filtering as suggested previously in the literature. Various scattering mechanisms were employed in the transport calculations and compared with the measured transport properties in nanostructured ZnSb as a function of temperature. Reasonable correspondence between theory and experiment could be achieved when a combination of constant lifetime scattering and energy filtering with a 0.25~eV barrier was employed. However, the difference between bulk and nanostructured samples was not sufficient to justify the introduction of an energy filtering mechanism. The reasons for this and possibilities to achieve filtering were discussed in the paper

FISH1D 2.1 User’s Manual

FISH1D is a computer program that solves the one-dimensional Poisson equation for electrostatic Fields In Semiconductor Heterostructures. The program will print or plot the electrostatic potential, electric field, electron and hole densities, dopant density, ionized dopant density, and other quantities of interest versus position at an applied bias voltage (assuming zero current). A capacitance or sheet carrier concentration versus voltage analysis may also be performed. While FISH1D was originally written for the ternary AlxGa1_xAs, it has been modified to simulate CdxHg1_xTe, ZnSe, GexSi1_x, and Si as well, and the program can be readily modified to analyze other semiconductors through the addition of new material subroutines or using the most recent option, the MATDEF card. This card enables the user to enter new material definitions by layers in the input deck without having to recompile, an advantage of FISH1D 2.1 over FISH1D 2.0. The primary purpose of this document is explain how to use FISH1D; for a more thorough discussion of the numerical implementation of FISH1D, the user is directed to the references. A theoretical basis for FISH1D is provided in Appendix I of this manual. The development of FISH1D was supported by the Semiconductor Research Corporation, the National Science Foundation Materials Research Laboratory, and by the Eastman Kodak Company

Crown Size-Arch Space Relationships During Human Prenatal Dental Development

As shown in composite reconstructions made from optically-projected measurements of 10μ frontal maxillofacial sections of 20 histologically normal fetuses and embryos in the 70-255 mm CRL range, individual differences in relative tooth size and interdental spacing are evident by 10.5-11 weeks of gestation, and age-corrected crown-size correlations (r=0.40) approximate those in postnatal life. Despite an eight-fold increase in crown dimensions, interdental spacing remains approximately constant after 150 mm CRL, suggesting that the tooth organs or the periodontal membranes are able to maintain spacing, into the third trimester.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67036/2/10.1177_00220345790580020301.pd