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The Numerov Process (NP) provides the solution of some classes of ODEs with an accuracy much superior to that of the standard finite-difference or box-integration methods. The original formulation of NP requires a uniform grid, which is a... more
The Numerov Process (NP) provides the solution of some classes of ODEs with an accuracy much superior to that of the standard finite-difference or box-integration methods. The original formulation of NP requires a uniform grid, which is a drawback for applications to, e.g., the semiconductor-device equations. Purpose of this work is showing how a method for extending NP to a non-uniform grid is applied to the solution of the drift-diffusion model. The method keeps the fifth-order accuracy of the original NP. In the multi-dimensional case, the variable transformation illustrated in the paper is found beneficial also when standard solution schemes are used; in fact, it makes the current-density vector well defined within each grid element.
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ABSTRACT
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ABSTRACT
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The electric response of Ovonic devices to a time-dependent voltage is analysed by means of a charge-transport model previously proposed by the authors. The numerical implementation of the model shows that the features of the I(V)... more
The electric response of Ovonic devices to a time-dependent voltage is analysed by means of a charge-transport model previously proposed by the authors. The numerical implementation of the model shows that the features of the I(V) characteristics depend not only upon the external bias but also on more complex effects due to the interplay between intrinsic microscopic relaxation times and the inevitable parasitic elements of the system. Either stable or oscillating solutions are found, according to the position of the load line. The model also allows for speculation on the potential of Ovonic materials in the design of selector devices for two-terminal non-volatile memories.
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Research Interests: Engineering, Computer Science, Radiation, Solar Cell, Semiconductor Devices, and 11 moreComputer Hardware, Software, Optical Sensor, Numerical Simulation, IEEE, Software Implementation, Discretization, Flexibility in engineering design, Spectrum, Electrical And Electronic Engineering, and Monochromatic Color
In this paper, we present an introduction to hydrodynamic-based simulation of semiconductor devices. A very general approach is given to illustrate a mathematical method of the solution. A general differential equation which is... more
In this paper, we present an introduction to hydrodynamic-based simulation of semiconductor devices. A very general approach is given to illustrate a mathematical method of the solution. A general differential equation which is characteristic of the relevant semiconductor equations is first presented and discussed. Solution of this general differential equation forms the basis of the mathematical model employed. A discretization
Research Interests: Physics, Semiconductor Devices, Semiconductor, Diffusion, Discretization, and 12 moreOptical physics, Mathematical Model, Device Simulation, Differential equation, Boundary Condition, Semiconductor Device, Boundary Value Problem, Electrical And Electronic Engineering, Figure of Merit, System of Equation Linear Equations, Bipolar Transistor, and Drift-diffusion
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The paper addresses the calculation of the band structure fordifferent phases of the chalcogenide Ge2Sb2Te5 compound,which is raising considerable interest in view of the applications tothe nonvolatile-memory technology. The band... more
The paper addresses the calculation of the band structure fordifferent phases of the chalcogenide Ge2Sb2Te5 compound,which is raising considerable interest in view of the applications tothe nonvolatile-memory technology. The band structure is necessary fordetermining the charge- and heat-transport properties of the material.The band diagram of the face-centered cubic phase, which is the mostimportant one for the operation of phase-change memories, is shown forthe first time
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A general expression is worked out for the trap-to-trap transition probability per unit time, applicable to amorphous materials where charge conduction is dominated by localized states. The outcome is a closed-form expression involving... more
A general expression is worked out for the trap-to-trap transition probability per unit time, applicable to amorphous materials where charge conduction is dominated by localized states. The outcome is a closed-form expression involving temperature and local electric potential. It is suitable for inclusion into hydrodynamic or energy-balance numerical solvers to be used for simulating devices based on amorphous materials.
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Single-stage H-bridge grid-connected inverters are considered as a simple, compact, and economic topology compared with double-stage converters. A maximum power point tracking (MPPT) control is necessary in photovoltaic (PV) generation... more
Single-stage H-bridge grid-connected inverters are considered as a simple, compact, and economic topology compared with double-stage converters. A maximum power point tracking (MPPT) control is necessary in photovoltaic (PV) generation system to extract maximum power from the PV arrays. Many MPPT techniques have been proposed and discussed in the literature. Among them, the ripple correlation control (RCC) algorithm is fast and effective, particularly suitable for single-phase configurations since it uses as perturbation the embedded oscillation of dc current and dc voltage at twice of grid frequency (e.g., 100 Hz). The main drawback of this method is the unstable behavior during sudden variation of sun irradiance, where the conventional RCC gives wrong estimation of the power derivative (dP/dV), causing wide dc voltage and dc current overshoots. To overcome this problem, a hybrid RCC-constant voltage regulator algorithm combined to a high-peformance dq grid current controller is proposed to improve the transient performance. The whole grid-connected photovoltaic generation scheme has been implemented numerically by MATLAB/Simulink, verifying steady-state and dynamic performances under different sun irradiance transients. The comparison with the corresponding behavior of a standard RCC algorithm emphasized the effectiveness of the proposed hybrid RCC controller.
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Some classes of differential equations are amenable to a numerical solution based on the Numerov process (NP), whose accuracy can be up to two orders of magnitude superior with respect to the standard finite-difference or box-integration... more
Some classes of differential equations are amenable to a numerical solution based on the Numerov process (NP), whose accuracy can be up to two orders of magnitude superior with respect to the standard finite-difference or box-integration methods, with a negligible increase in the computational cost. The paper shows that the equations describing charge transport in solid-state devices can suitably be manipulated to make the application of NP possible. Also, thanks to a specifically-tailored algebraic solver, the 1D Poisson equation is fully decoupled from the transport equation, this reducing the procedure to the solution of a single non-linear equation. The example of an Ovonic device is considered, used as selector in phase-change memory applications.
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The first part of this chapter illustrates the diffusive transport with reference to the processes that are used for introducing impurities into a semiconductor in a controlled way. First, the expressions of the continuity equation and of... more
The first part of this chapter illustrates the diffusive transport with reference to the processes that are used for introducing impurities into a semiconductor in a controlled way. First, the expressions of the continuity equation and of the diffusive flux density are derived. These expressions are combined to yield the diffusion equation, whose form is reduced to a one-dimensional model problem. The model problem allows for an analytical solution that expresses the diffused profile at each instant of time as the convolution of the initial condition and an auxiliary function. Then, the solution of the model problem is used to calculate the impurity profiles resulting from two important processes of semiconductor technology, namely, the predeposition and the drive-in diffusion. Then, the solution of the model problem is extended to more general situations. The last part of this chapter illustrates the features of ion implantation; it starts from the description of the ion implanter,...
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In this paper the implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is discussed in case of multiple ripple harmonics. As an example, a single-phase single-stage grid-connected... more
In this paper the implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is discussed in case of multiple ripple harmonics. As an example, a single-phase single-stage grid-connected photovoltaic (PV) system based on H-bridge inverter and level doubling network (LDN) is considered, leading to a multilevel inverter having the double of output voltage levels compared to the basic H-bridge inverter topology. The LDN is basically a half-bridge fed by a floating capacitor, with voltage self-balancing capability. In this case, additional voltage and current harmonics are introduced in the dc-bus of the H-bridge, leading to multiple PV voltage and current low-order harmonics comparing to the double fundamental frequency component in case of basic H-bridge configuration. Voltage and current harmonic components are used in RCC schemes to estimate dP/dV and to drive the PV operating point to the MPP. Different possible dP/dV estimations have been proposed in case of multiple harmonics, and a specific case with LDN has been considered. The steady-state and transient performances of the proposed RCC-MPPT schemes have been numerically tested and compared by MATLAB/Simulink.
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The ADEQUAT project [Advanced Developments for Quarter Micron complementary metal–oxide–semiconductor (CMOS) Technologies] is executed by a European consortium under the JESSI/ESPRIT programs. It aims at developing new device structures... more
The ADEQUAT project [Advanced Developments for Quarter Micron complementary metal–oxide–semiconductor (CMOS) Technologies] is executed by a European consortium under the JESSI/ESPRIT programs. It aims at developing new device structures and process modules for the 0.35 and 0.25 μm CMOS logic technology generations, offering improved performance while meeting the reliability and manufacturability constraints. Several examples of choices illustrating this optimization process are presented together with the overall project organization and roadmap.
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In the quasi-classical approximation, the theory of fluctuations in a degenerate two-or three-dimensional non-equilibrium electron gas is developed from first principles. It is shown that, thanks to the small-angle character of the... more
In the quasi-classical approximation, the theory of fluctuations in a degenerate two-or three-dimensional non-equilibrium electron gas is developed from first principles. It is shown that, thanks to the small-angle character of the inter-electron scattering, the theory takes a rather simple and transparent form, in contrast to other types of Fermi gases for which, due to exchange effects, the situation proves to be much more complicated.
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A number of methods used for measuring the semiconductor parameters are illustrated here. Apart from the intrinsic usefulness, the methods are interesting because they show the connection with the theories worked out in other chapters.... more
A number of methods used for measuring the semiconductor parameters are illustrated here. Apart from the intrinsic usefulness, the methods are interesting because they show the connection with the theories worked out in other chapters. For example, the measurement of lifetimes exploits the features of the net thermal recombination and of optical generation, that are combined in a simplified form of the continuity equation for the minority carriers. Similarly, the measurement of mobility carried out with the Haynes-Shockley experiment is based on a clever use of the diffusion of optically generated carriers. The Hall effect, in turn, provides a powerful method to extract the information about the concentration and mobility of the majority carriers; the method exploits the effect of a magnetic field applied in the direction normal to that of the current density, and is widely used for determining, e.g., the dependence of concentration and mobility on the concentration of dopants and on temperature. The analysis of the Hall effect is enriched by a detailed treatment of the case where the standard theory is not applicable because the device is not sufficiently slender; a deeper analysis based on the concept of stream function shows that the equations describing the current-density field are in fact solvable for any aspect ratio of the device. This chapter is completed by the illustration of a method for measuring the doping profile in an asymmetric, reverse-biased, one-dimensional junction; the procedure is based on the observation that despite the fact that the relation between the applied voltage and the extension of the space-charge region is nonlinear, the differential capacitance of the junction has the same form as that of a parallel-plate, linear capacitor. Finally, the van der Pauw method for measuring the conductivity of a sample is illustrated, based on the use of a two-dimensional Green function introduced in an earlier chapter and on the conformal-mapping method shown in the Appendix.