KEYWORDS: Microchannel plates, Terahertz radiation, Capacitance, Signal to noise ratio, Monte Carlo methods, Interference (communication), Solids, Fourier transforms, Diodes, Resistance
We report Monte Carlo particle (MCP) simulations of the current response and noise spectrum in heavily doped nanometric GaAs Schottky-barrier diodes (SBDs) operating under static, cyclostationary and resonant-circuit conditions in the forward bias region. Main attention is paid to the SBDs application in the THz frequency region. General features of the regular response and noise as well as their modifications under various operation modes are obtained from MCP simulations and analyzed in the framework of a simple analytical model based on the static I-V and C-V relations obtained from simulations.
We present for the first time a complex network approach to the study of the electrical properties of single protein devices. In particular, we consider an electronic nanobiosensor based on a G-protein coupled receptor. By adopting a coarse grain description, the protein is modeled as a complex network of elementary impedances. The positions of the alpha-carbon atoms of each amino acid are taken as the nodes of the network. The amino acids are assumed to interact electrically among them. Consequently, a link is drawn between any
pair of nodes neighboring in space within a given distance and an elementary impedance is associated with each link. The value of this impedance can be related to the physical and chemical properties of the amino acid pair and to their relative distance. Accordingly, the conformational changes of the receptor induced by the capture of the ligand, are translated into a variation of its electrical properties. Stochastic fluctuations in the value of the elementary impedances of the network, which mimic different physical effects, have also been considered. Preliminary results concerning the impedance spectrum of the network and its fluctuations are presented and discussed for
different values of the model parameters.
This paper overviews and implements the transfer-field method
applied to the calculation of electronic noise in small
semiconductor structures. Two basic schemes are used and developed
in detail. The former considers velocity fluctuations and the
latter acceleration fluctuations as microcopic noise sources. We
show that the latter scheme has several advantages with respect to
the former one. Indeed, starting from Markovian noise sources, the
latter scheme separates the time and spatial evolution of the
local noise sources. In this way, the dual representation of the
noise spectral density in terms of impedance and admittance fields
is recovered. A remarkable achievement is that from the knowledge
of the bulk Langevin sources at a hydrodynamic level it is
possible to calculate the noise spectra of non-homogeneous
structures even for nanometric devices. The method is validated by
comparing the results of the present scheme with those obtained
from self-consistent Monte Carlo approaches for different
structures of interest.
We study the distribution of resistance fluctuations of conducting thin films with different levels of internal disorder. The film is modeled as a resistor network in a steady state determined by the competition between two biased processes, breaking and recovery of the elementary resistors. The fluctuations of the film resistance are calculated by Monte Carlo simulations which are performed under different bias conditions, from the linear regime up to the threshold for electrical breakdown. Depending on the value of the external current, on the level of disorder and on the size of the system, the distribution of the resistance fluctuations can exhibit significant deviations from Gaussianity. As a general trend, a size dependent, non universal distribution is found for systems with low and intermediate disorder. However, for strongly disordered systems, close to the critical point of the conductor-insulator transition, the non-Gaussianity persists when the size is increased and the distribution of resistance fluctuations is well described by the universal Bramwell-Holdsworth-Pinton distribution.
The investigation of noise in electronic devices operating under large-signal conditions is attracting increasing attention in recent years. Theoretical analyses on this subject are typically performed in the framework of the impedance field method, implemented under the drift-diffusion approximation. As an alternative, a more general microscopic approach including a more detailed physical description of the systems is mandatory. This work reviews recent results of Monte Carlo simulations of electronic noise in bulk materials and submicron semiconductor structures subject to high-frequency large-amplitude periodic electric fields or applied voltages/currents.
The peculiarity of the noise analysis under large-signal operation is that velocity or current/voltage fluctuations appear simultaneously with the regular response of the nonlinear medium or device, so that the regular response and noise spectra are overlapped in the whole frequency range of interest. Here, various correlation functions of fluctuations, their instantaneous and integrated spectral densities, etc. are calculated under large-signal operation for compound semiconductors, such as GaAs, and InN, as well as for GaAs Schottky-barrrier diodes and n+nn+ structures. A comparison with the results obtained under stationary conditions is performed. Under these large-signal cyclostationary working conditions, when the system response becomes nonlinear, several modifications and anomalies appear in the noise spectra with respect to static stationary conditions. In particular, an increase of the low-frequency noise and a resonant-like enhancement of the spectra near the fundamental frequency (and eventually high-order harmonics) of the applied signal is observed under some specific conditions. These anomalies are interpreted as a manifestation of dynamical effects under sufficiently high frequency and amplitude of the applied signal. Similarities and differences of the noise resonant-like enhancement around the fundamental frequency with noise upconversion processes are discussed.
We survey a theoretical investigation of shot-noise in single and multiple barrier diodes. Several mechanisms responsible of the suppression of shot noise are reviewed together with the conditions for obtaining shot noise enhancement. The coherent versus sequential tunneling model for the double barrier resonant diode is discussed in the light of existing experiments.
Amplification and generation of microwave radiation by optical phonon transit-time resonance GaN THz maser is investigated theoretically by Monte Carlo simulations. Results confirm that GaN is a promising material for THz power generation. The amplification and generation occurs in the wide frequency range of 0.3 to 3 THz and persists in the THz frequency range up to liquid nitrogen temperatures and doping levels of about 5 X 1016 cm-3.
KEYWORDS: Monte Carlo methods, Sensors, X-rays, Gallium arsenide, Electrons, X-ray detectors, Energy efficiency, Signal detection, Signal attenuation, Astatine
We have developed a Monte Carlo simulator for semi- insulating GaAs detectors which gives the energy spectra of x-ray radiations. The simulated spectra are analyzed in terms of: shaping time, trapping properties of the material, and applied reverse voltage. The main features of the spectra as well as the associated charge collection efficiency and the energy resolution of the photoelectric peak are interpreted in physical terms for the whole range of applied voltages covering under- and over-depleted conditions. The results of the simulations provide a general interpretation scheme which is satisfactorily tested with experimental results.
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