19,891 research outputs found
Simulation of intrinsic parameter fluctuations in decananometer and nanometer-scale MOSFETs
Intrinsic parameter fluctuations introduced by discreteness of charge and matter will play an increasingly important role when semiconductor devices are scaled to decananometer and nanometer dimensions in next-generation integrated circuits and systems. In this paper, we review the analytical and the numerical simulation techniques used to study and predict such intrinsic parameters fluctuations. We consider random discrete dopants, trapped charges, atomic-scale interface roughness, and line edge roughness as sources of intrinsic parameter fluctuations. The presented theoretical approach based on Green's functions is restricted to the case of random discrete charges. The numerical simulation approaches based on the drift diffusion approximation with density gradient quantum corrections covers all of the listed sources of fluctuations. The results show that the intrinsic fluctuations in conventional MOSFETs, and later in double gate architectures, will reach levels that will affect the yield and the functionality of the next generation analog and digital circuits unless appropriate changes to the design are made. The future challenges that have to be addressed in order to improve the accuracy and the predictive power of the intrinsic fluctuation simulations are also discussed
Model for self-consistent analysis of arbitrary MQW structures
Self-consistent computations of the potential profile in complex
semiconductor heterostructures can be successfully applied for comprehensive
simulation of the gain and the absorption spectra, for the analysis of the
capture, escape, tunneling, recombination, and relaxation phenomena and as a
consequence it can be used for studying dynamical behavior of semiconductor
lasers and amplifiers. However, many authors use non-entirely correct ways for
the application of the method. In this paper the versatile model is proposed
for the investigation, optimization, and the control of parameters of the
semiconductor lasers and optical amplifiers which may be employed for the
creation of new generations of the high-density photonic systems for the
information processing and data transfer, follower and security arrangements.
The model is based on the coupled Schredinger, Poisson and drift-diffusion
equations which allow to determine energy quantization levels and wave
functions of charge carriers, take into account built-in fields, and to
investigate doped MQW structures and those under external electric fields
influence. In the paper the methodology of computer realization based on our
model is described. Boundary conditions for each equation and consideration of
the convergence for the method are included. Frequently encountered in practice
approaches and errors of self-consistent computations are described. Domains of
applicability of the main approaches are estimated. Application examples of the
method are given. Some of regularities of the results which were discovered by
using self-consistent method are discussed. Design recommendations for
structure optimization in respect to managing some parameters of AMQW
structures are given.Comment: 12 pages, 2 table, 4 figures, Optics East Symposium, Conference on
Physics and Applications of Optoelectronic Devices, October 25-28, 2004,
Philadelphia, Pennsylvania, US
When self-consistency makes a difference
Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of selfconsistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. In this contribution we show two examples, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling is proved to be be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximations; in the discussion we exploit a Wiener approach, but of course the strategy should be tailored to the specific problem under consideratio
Carrier Transport in High Mobility InAs Nanowire Junctionless Transistors
Ability to understand and model the performance limits of nanowire
transistors is the key to design of next generation devices. Here, we report
studies on high-mobility junction-less gate-all-around nanowire field effect
transistor with carrier mobility reaching 2000 cm2/V.s at room temperature.
Temperature-dependent transport measurements reveal activated transport at low
temperatures due to surface donors, while at room temperature the transport
shows a diffusive behavior. From the conductivity data, the extracted value of
sound velocity in InAs nanowires is found to be an order less than the bulk.
This low sound velocity is attributed to the extended crystal defects that
ubiquitously appear in these nanowires. Analyzing the temperature-dependent
mobility data, we identify the key scattering mechanisms limiting the carrier
transport in these nanowires. Finally, using these scattering models, we
perform drift-diffusion based transport simulations of a nanowire field-effect
transistor and compare the device performances with experimental measurements.
Our device modeling provides insight into performance limits of InAs nanowire
transistors and can be used as a predictive methodology for nanowire-based
integrated circuits.Comment: 22 pages, 5 Figures, Nano Letter
Synchronization of spatiotemporal semiconductor lasers and its application in color image encryption
Optical chaos is a topic of current research characterized by
high-dimensional nonlinearity which is attributed to the delay-induced
dynamics, high bandwidth and easy modular implementation of optical feedback.
In light of these facts, which adds enough confusion and diffusion properties
for secure communications, we explore the synchronization phenomena in
spatiotemporal semiconductor laser systems. The novel system is used in a
two-phase colored image encryption process. The high-dimensional chaotic
attractor generated by the system produces a completely randomized chaotic time
series, which is ideal in the secure encoding of messages. The scheme thus
illustrated is a two-phase encryption method, which provides sufficiently high
confusion and diffusion properties of chaotic cryptosystem employed with unique
data sets of processed chaotic sequences. In this novel method of cryptography,
the chaotic phase masks are represented as images using the chaotic sequences
as the elements of the image. The scheme drastically permutes the positions of
the picture elements. The next additional layer of security further alters the
statistical information of the original image to a great extent along the
three-color planes. The intermediate results during encryption demonstrate the
infeasibility for an unauthorized user to decipher the cipher image. Exhaustive
statistical tests conducted validate that the scheme is robust against noise
and resistant to common attacks due to the double shield of encryption and the
infinite dimensionality of the relevant system of partial differential
equations.Comment: 20 pages, 11 figures; Article in press, Optics Communications (2011
Numerical simulation of neutron radiation effects in avalanche photodiodes
A new one-dimensional (1-D) device model developed for the simulation of neutron radiation effects in silicon avalanche photodiodes is described. The model uses a finite difference technique to solve the time-independent semiconductor equations across a user specified structure. The model includes impact ionization and illumination allowing accurate simulation with minimal assumptions. The effect of neutron radiation damage is incorporated via the introduction of deep acceptor levels subject to Shockley-Read-Hall statistics. Preliminary analysis of an EG&G reverse APD structure is compared with experimental data from a commercial EG&G C30719F APD
Monte Carlo Modeling of Spin FETs Controlled by Spin-Orbit Interaction
A method for Monte Carlo simulation of 2D spin-polarized electron transport
in III-V semiconductor heterojunction FETs is presented. In the simulation, the
dynamics of the electrons in coordinate and momentum space is treated
semiclassically. The density matrix description of the spin is incorporated in
the Monte Carlo method to account for the spin polarization dynamics. The
spin-orbit interaction in the spin FET leads to both coherent evolution and
dephasing of the electron spin polarization. Spin-independent scattering
mechanisms, including optical phonons, acoustic phonons and ionized impurities,
are implemented in the simulation. The electric field is determined
self-consistently from the charge distribution resulting from the electron
motion. Description of the Monte Carlo scheme is given and simulation results
are reported for temperatures in the range 77-300 K.Comment: 18 pages, 7 figure
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