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1 – 10 of 24In this paper, it can be seen from AFM images of the as-deposited ZnO and CZO films, and the particle size and shape are not clear, while by increasing annealing temperature, they…
Abstract
Purpose
In this paper, it can be seen from AFM images of the as-deposited ZnO and CZO films, and the particle size and shape are not clear, while by increasing annealing temperature, they become distinguishable. By increasing temperature to 600°C, ZnO and CZO, CAZO and aluminum-doped zinc oxide (AZO) films particles became almost spherical. Due to high content of Cu in CZO target, and of Al in AZO target which was 5% weight ratio, doping plays a great role in the subject. Therefore, the annealing processing strongly affect the size and the shape of nanoparticles.
Design/methodology/approach
In this paper, the authors tried to study, in detail, nobel optical characterizations of ZnO films doped by transition metals in different annealing temperature. The authors found that the values of skin depth, optical density, electron–phonon interaction, steepness parameter, band tail width, direct and indirect carriers transitions and the dissipation factor, free carriers density and roughness of films affect the optical properties, especially the optical absorptions of ZnO films doped by transition metals. Also these properties were affected by annealing temperatures. The authors also found that topography characterizations strongly were affected by these parameters.
Findings
The CZO films have maximum value of coordination number ß, with considering NC = 4, Za = 2, Ne = 8. The CZO films annealed at 500 °C have maximum value of optical density. The as-deposited CAZO films have maximum value of steepness parameters in about of 0.13 eV. The as-deposited AZO films have maximum value of dispersion energy Ed in about of 5.75 eV. Optical gap and disordering energy plots of films can be fitted by linear relationships Eg = 0.49 + 0.2 EU and Eg = 0.52 + 0.5 EU, respectively.
Originality/value
With considering Nc = 4, Za = 2, Ne = 8 for ZnO films, coordination number ß has maximum value of 0.198. CZO nanocomposites films annealed at 500°C have maximum value of optical density. Different linear fitting of ln (α) for films were obtained as y = Ax + B where 5<A < 17 and 5<B < 12. As-deposited CAZO nanocomposites films have minimum value of electron phonon interaction in about of 4.91 eV. Optical gap and disordering energy plots can be fitted by linear relationships Eg = 0.49 + 0.2 EU and Eg = 0.52 + 0.5 EU for as-deposited films and films annealed at 500°C, respectively. Steepness parameters of as-deposited CAZO nanocomposites films have maximum value of 0.13 eV. Dispersion energy Ed for as-deposited AZO nanocomposites films has maximum value of 5.75 eV.
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Karel Král and Miroslav Menšík
In this work the experimental effect of a slow decay of the photoluminescence is studied theoretically in the case of quantum dots with an indirect energy band gap. The slow decay…
Abstract
In this work the experimental effect of a slow decay of the photoluminescence is studied theoretically in the case of quantum dots with an indirect energy band gap. The slow decay of the photoluminescence is considered as decay in time of the luminescence intensity, following the excitation of the quantum dot sample electronic system by a short optical pulse. In the presented theoretical treatment the process is studied as a single dot property. The inter-valley deformation potential interaction of the excited conduction band electrons with lattice vibrations is considered in the self-consistent Born approximation to the electronic self-energy. The theory is built on the non-equilibrium electronic quantum transport theory. The time dependence of the photoluminescence decay is estimated upon using a simple effective mass model. The numerical calculation of the considered model shows the power-law time characteristics of the photoluminescence decay in the long-time limit of the decay. We demonstrate that the nonadiabatic influence of the interaction of the conduction band electrons with the lattice vibrations provides a mechanism giving us the power-law time dependence of the photoluminescence intensity signal. This theoretical result emphasizes the role of the electron-phonon interaction in the nanostructures.
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Presents a simplified mathematical model of electron transport in a one‐dimensional semiconductor device of N+ ‐ N ‐ N + type. The model is based on a singular perturbation…
Abstract
Presents a simplified mathematical model of electron transport in a one‐dimensional semiconductor device of N+ ‐ N ‐ N + type. The model is based on a singular perturbation approach of the kinetic equation which describes the transport processes. This so‐called Child‐Langmuir asymptotics is obtained by assuming that the injected electrons at the N + ‐ N junction on the source side have a very weak energy compared with what they are able to gain under the influence of the electric field. Formally establishes the limit model when a realistic collision model for electron‐phonon interaction is considered. Compares the results with both experiments and particle simulations.
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A transport model has been developed which is reasonably accurate, and has proven quite efficient for the two‐dimensional numerical simulation of submicron‐scale Si and GaAs…
Abstract
A transport model has been developed which is reasonably accurate, and has proven quite efficient for the two‐dimensional numerical simulation of submicron‐scale Si and GaAs devices. In this model an approximate form of the energy‐transport equation is developed; this equation is easily included in otherwise‐conventional device simulation codes, which then require only slightly more solution time than standard models using field‐dependent transport coefficients. Calculations for 0.25 micron gate length Si and GaAs MESFET's show that velocity overshoot effects can be very important, particularly in the latter material; predicted saturation currents in the GaAs devices are almost three times larger than those that would have been predicted using conventional transport models. The model described, and its application in simulation programs, should find use in the design of submicron‐scale devices to properly take advantage of overshoot phenomena.
A. Majorana, O. Muscato and C. Milazzo
Time‐depending solutions to the Boltzmann‐Poisson system in one spatial dimension and three‐dimensional velocity space are obtained by using a recent finite difference numerical…
Abstract
Time‐depending solutions to the Boltzmann‐Poisson system in one spatial dimension and three‐dimensional velocity space are obtained by using a recent finite difference numerical scheme. The collision operator of the Boltzmann equation models the scattering processes between electrons and phonons assumed in thermal equilibrium. The numerical solutions for bulk silicon and for a one‐dimensional n+‐n‐n+ silicon diode are compared with the Monte Carlo simulation. Further comparisons with the experimental data are shown.
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A simple interaction‐potential model has been established to calculate the higher order elastic constants of intermetallic YbAl2 in the temperature range from 10‐300K. Temperature…
Abstract
A simple interaction‐potential model has been established to calculate the higher order elastic constants of intermetallic YbAl2 in the temperature range from 10‐300K. Temperature dependent second and third order elastic constants are used for the determination of the ultrasonic attenuation, velocity, Grüneisen numbers, Acoustic‐coupling constants, and thermal relaxation time at the different temperatures. Temperature dependency of the ultrasonic properties of YbAl2 is similar at low temperatures to that of pure metals and the low carrier heavy fermion systems ‐ LaSb, YbAs and YbP having simple NaCl‐type structures. Thermal energy density makes significant contribution to the total attenuation in the compound at the higher temperatures from 100‐300K. Effect of the magnetic field on the ultrasonic attenuation is also evaluated using the magneto resistance data. At 100K, the effect of the magnetic field becomes insignificant. The attenuation decreases with the field at 3K to 50K.
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Orazio Muscato, Wolfgang Wagner and Vincenza Di Stefano
– The purpose of this paper is to deal with the self-heating of semiconductor nano-devices.
Abstract
Purpose
The purpose of this paper is to deal with the self-heating of semiconductor nano-devices.
Design/methodology/approach
Transport in silicon semiconductor devices can be described using the Drift-Diffusion model, and Direct Simulation Monte Carlo (MC) of the Boltzmann Transport Equation.
Findings
A new estimator of the heat generation rate to be used in MC simulations has been found.
Originality/value
The new estimator for the heat generation rate has better approximation properties due to reduced statistical fluctuations.
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Hydrodynamic‐like models are commonly used for describing carrier transport in semiconductor devices. One major problem of this formulation is how to model the production terms…
Abstract
Hydrodynamic‐like models are commonly used for describing carrier transport in semiconductor devices. One major problem of this formulation is how to model the production terms. In this paper the relaxation‐time approximation and the moments expansion of the production terms are checked with Monte Carlo simulations for a one dimensional n+ – n – n+ silicon diode in the spherical parabolic band approximation.
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A.M. ANILE, C. MACCORA and R.M. PIDATELLA
The effects of viscosity, previously neglected in electronic device stimulations, are studied using a non‐standard hydrodynamic model, following Anile and Pennisi. Results are…
Abstract
The effects of viscosity, previously neglected in electronic device stimulations, are studied using a non‐standard hydrodynamic model, following Anile and Pennisi. Results are compared with those of Gardner.
Orazio Muscato and Wolfgang Wagner
To provide an accurate analysis of the systematic error introduced by the constant time technique free flight mechanism, due to the choice of the time step and number particles.
Abstract
Purpose
To provide an accurate analysis of the systematic error introduced by the constant time technique free flight mechanism, due to the choice of the time step and number particles.
Design/methodology/approach
A homogeneous (bulk) silicon semiconductor is studied by using direct simulation Monte Carlo (DSMC).
Findings
The systematic error turns out to be of the first order with respect to the time step. The efficiency of the method is tackled.
Research limitations/implications
The analysis is limited to the bulk case. Future researches will consider non homogeneous devices
Originality/value
An accurate analysis of an “old” free flight mechanism has been performed, and its limits have been stated.
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