Semiconductor Model Research Articles

Potential error from using ZT to optimize thermoelectric performance

Despite known shortcomings, the dimensionless figure of merit, ZT, continues to be the most widely used material performance metric in thermoelectrics research. Here, we expose yet another potential drawback of using the ZT to evaluate new thermoelectric materials. Specifically, by comparison with more accurate methods of estimating thermoelectric material energy conversion efficiency, we find that using the ZT as the optimization criterion could possibly lead to erroneous conclusions about the optimal doping density when optimizing performance. Using a simple semiconductor model, we find that optimal doping densities as determined using the ZT could be in error by a factor of two or more, potentially contributing a relatively small but non-negligible loss in device efficiency that could be easily avoided by using modern methods for estimation of material conversion efficiency.

A Novel Three-Pulse Equivalent Power Loss Profile for Simplified Thermal Estimation

One of the key challenges for long-term reliability analysis of power electronic converters is to quickly estimate extensive junction temperature cycles of power semiconductor devices while fulfilling an accepted accuracy. To address this challenge, this article proposes a novel three-pulse equivalent power loss profile. By contrast to the conventional methods of dividing the power loss equally, this article discretizes the power loss profile based on the identified occurrences of maximum and minimum junction temperatures (i.e., thermal characteristics). This proposed model decouples the conventional conflict between the thermal estimation accuracy and computational burdens. And it has the advantages of improving accuracy in terms of the maximum and minimum junction temperatures, and power-on time of thermal profiles, which are majorly concerned by today’s lifetime models of power semiconductors. Moreover, the proposed method also helps to reduce computational burdens. The relevant variables of the thermal modeling methods are investigated. Finally, the effectiveness of the proposed method is verified through simulation and experiments, and the impact of its thermal estimation advantages on lifetime evaluation is analyzed further.

Influence of surface band bending on a narrow band gap semiconductor: Tunneling atomic force studies of graphite with Bernal and rhombohedral stacking orders

Tunneling atomic force microscopy (TUNA) was used at ambient conditions to measure the current-voltage ($I$-$V$) characteristics at clean surfaces of highly oriented graphite samples with Bernal and rhombohedral stacking orders. The characteristic curves measured on Bernal-stacked graphite surfaces can be understood with an ordinary self-consistent semiconductor modeling and quantum mechanical tunneling current derivations. We show that the absence of a voltage region without measurable current in the $I$-$V$ spectra is not a proof of the lack of an energy band gap. It can be induced by a surface band bending due to a finite contact potential between tip and sample surface. Taking this into account in the model, we succeed to obtain a quantitative agreement between simulated and measured tunnel spectra for band gaps $(12 \ldots 37)$\,meV, in agreement to those extracted from the exponential temperature decrease of the longitudinal resistance measured in graphite samples with Bernal stacking order. In contrast, the surface of relatively thick graphite samples with rhombohedral stacking reveals the existence of a maximum in the first derivative $dI/dV$, a behavior compatible with the existence of a flat band. The characteristics of this maximum are comparable to those obtained at low temperatures with similar techniques.

Radial solutions of hydrodynamic model of semiconductors with sonic boundary

The purpose of this paper is to study the multi-dimensional steady hydrodynamic model of semiconductors represented by Euler-Poisson equations with sonic boundary. We prove that, the steady Euler-Poisson equations with sonic boundary possess a unique subsonic solution and at least one supersonic solution in the radial form. The adopted approach for proof is the energy method combining the compactness analysis. For the n-D radial supersonic solutions, since it is more challenging to get the crucial energy estimates due to the effect by the multiple dimensions and the restriction by the sonic boundary, we propose a brand new two-steps iteration scheme to build up the key energy estimates. This is the first attempt to study the n-D steady-states with the sonic boundary, and the results obtained essentially improve and develop the previous studies in the one-dimensional case.

Avant-grade magneto/fluorescent nanostructures for biomedical applications: Organized and comprehensive optical and magnetic evaluation

State-of-the-art core@shell multifunctional nanostructures were prepared that are capable to serve the need of magneto/fluorescent characteristics in a single unit. CdS quantum dots (QD’s) shell was successfully developed upon the SrFe 12O19 nanoparticles core surface and a clear add-on was observed from UV–visible spectroscopy, photoluminescence spectroscopy, VSM and FTIR, with high stability and intactness of core and shell. Optical studies provide in-depth information about development of any new phase at the interface and reject all the possibilities of defects or in core@shell structures. Stoner–Wohlfarth value manifests the single magnetic domain structures for the core@shell nanostructures. Uniaxial anisotropy was achieved with single easy direction. Using water for the synthesis augments the applications zone of these nanostructures specifically in the field of biology. This magnet inside semiconductor model fulfil the need of targeting and tracking at the same time and thus proved to be very useful tool in targeted drug delivery, administer as a dual-modal imaging probe for in vivo multi-photon cell-dynamics, MRI; and cell-sorting applications. Different sets of core/shell nanostructures were synthesized to optimize the best Strontium hexa ferrite (SHF) core loading and shell particle size to achieve finest composition with finest “magneto fluorescent” properties.

A high order multi-resolution WENO numerical scheme for solving viscous quantum hydrodynamic model for semiconductor devices

In this article, fifth order finite volume multi-resolution weighted essentially non-oscillatory (MR-WENO) scheme is developed for solving one-dimensional non linear viscous quantum hydrodynamical model for semiconductor devices with constant temperature. This non linear model consists of three equations, two equations for the current density and electron density, and third equation is the Poisson equation. The first two equations include the viscous and quantum correction terms. Further, numerical technique is used to obtain the solution due to high non linearity of considered model. The multi-resolution technique is used to reduce the computational cost of high resolution numerical scheme. In the procedure of derivation of the MR-WENO scheme unequal central spatial stencils are used and linear weights can be chosen any positive numbers with only restriction that their total sum is one. Various numerical test problems are considered to check the validity and accuracy of the derived numerical scheme. Further, the results obtained from considered numerical scheme are compared with those of kinetic flux vector splitting numerical scheme.

FT-IR, Molecular Structure and Nonlinear Optical Properties of 2-(pyranoquinolin-4-yl)malononitrile (PQMN): A DFT Approach

A combined experimental and theoretical study for Fourier transform infrared spectra for 2-(pyranoquinolin-4-yl)malononitrile (PQMN) compound has been made. In advance, we investigate many physical characteristics based on DFT/B3LYP using 6-311G(d,p) basis set such as optimum structure, vibrational frequencies, thermo-chemistry, overall dipole moment, HOMO/LUMO Bandgap, nuclear repulsive energy and ionization energies, electronic affinity and chemical potential, global electrophilicity index, global hardness and finally softness (ζ). Also, we studied the non-linear optical (NLO) properties of PQMN. Results emphasize both degeneracy and diamagnetic properties of PQMN. PQMN Frontiers’ molecular orbitals (FMOs) split into two distinguished alpha (spin ↑) and beta (spin ↓) states with the same energy 3.7 eV, although its singlet spins state. Moreover, the calculated dipole moment (DM) value (13.3 Debye) for PQMN explains the mystery behind its reactive tendency with the nearby media. PQMN is a unique model for a degenerate diamagnetic semiconductor that can be easily used for optoelectronic manufactured devices such as solar cells and spintronic devices.

Interleaved, Switched Inductor and High-Gain Wide Bandgap Based Boost Converter Proposal

Many applications (electric vehicles, renewable energies, low-voltage DC grids) require simple, high-power density and low-current ripple-boost converters. Traditional step-up converters are limited when large transformation ratios are involved. In this work is proposed a step-up converter that brings together the characteristics of high gain, low ripple, and high-power density. From the converter proposal, a mathematical analysis of its operation is first performed, including its static transfer function, stress of components, and voltage and current ripples. Furthermore, it provides a design example for an application of Vin = 48 V to Vo = 270 V and 500 W. For its implementation, two different wide bandgap (WBG) semiconductor models have been used, hybrid GaN cascodes and SiC MOSFETs. Finally, the experimental results of the produced prototypes are shown, and the results are discussed.

Monte carlo optimization of multi-layer semiconductor material

At present, the demand for various types of semiconductor devices is increasing, and under the current situation of energy shortage, the improvement of the energy efficiency of semiconductors is the top priority for development of science and technology. For this purpose, this article establishes a physical model and mathematical optimization model for multi-layer semiconductors based on Monte Carlo Simulation. The developed model and corresponding equations are derived from thermodynamic theory and principles, and the computer programming is set up to get the optimal design of multilayer semiconductors through Monte Carlo simulation to achieve higher energy efficiency.

Generalized Boltzmann relations in semiconductors including band tails

Boltzmann relations are widely used in semiconductor physics to express the charge-carrier densities as a function of the Fermi level and temperature. However, these simple exponential relations only apply to sharp band edges of the conduction and valence bands. In this article, we present a generalization of the Boltzmann relations accounting for exponential band tails. To this end, the required Fermi–Dirac integral is first recast as a Gauss hypergeometric function followed by a suitable transformation of that special function and a zeroth-order series expansion using the hypergeometric series. This results in simple relations for the electron and hole densities that each involve two exponentials. One exponential depends on the temperature and the other one on the band-tail parameter. The proposed relations tend to the Boltzmann relations if the band-tail parameters tend to zero. This work is timely for the modeling of semiconductor devices at cryogenic temperatures for large-scale quantum computing.

Existence and uniqueness of solution for multidimensional parabolic partial differential‐algebraic equations arising in semiconductor modeling

This paper concerns with a compact network model combined with distributed models for semiconductor devices. For linear RLC networks containing distributed semiconductor devices, we construct a mathematical model that joins the differential‐algebraic initial value problem for the electric circuit with multidimensional parabolic‐elliptic boundary value problems for the devices. We prove an existence and uniqueness result and the asymptotic behavior of this mixed initial boundary value problem of partial differential‐algebraic equations.

Stability of steady-state for 3-D hydrodynamic model of unipolar semiconductor with Ohmic contact boundary in hollow ball

The existence of stationary subsonic solutions and their stability for 3-D hydrodynamic model of unipolar semiconductors with the Ohmic contact boundary have been open for long time due to some technical reason, as we know. In this paper, we consider 3-D radial solutions to the system in a hollow ball, and prove that the 3-D radial subsonic stationary solutions uniquely exist and are asymptotically stable, when the initial perturbations around the subsonic steady-state are small enough. Different from the existing studies on the radial solutions for fluid dynamics where the inner boundary of the hollow ball must be far away from the singular origin, here we may allow the chosen inner boundary arbitrarily close to the singular origin and reveal the relationship between the inner boundary and the large time behavior of the radial solution. This partially answers the open question of the stability of stationary waves subjected to the Ohmic contact boundary conditions in the multiple dimensional space. We also prove the existence of non-flat stationary subsonic solution, which essentially improve and develop the previous studies in this subject. The proof is based on the technical energy estimates in certain weighted Sobolev spaces, where the weight functions are artfully selected to be the distance of the targeted spatial location and the singular point.

High-harmonic generation in one-dimensional Mott insulators

We study high-harmonic generation (HHG) in the one-dimensional Hubbard model in order to understand its relation to elementary excitations as well as the similarities and differences to semiconductors. The simulations are based on the infinite time-evolving block decimation (iTEBD) method and exact diagonalization. We clarify that the HHG originates from the doublon-holon recombination, and the scaling of the cutoff frequency is consistent with a linear dependence on the external field. We demonstrate that the subcycle features of the HHG can be reasonably described by a phenomenological three step model for a doublon-holon pair. We argue that the HHG in the one-dimensional Mott insulator is closely related to the dispersion of the doublon-holon pair with respect to its relative momentum, which is not necessarily captured by the single-particle spectrum due to the many-body nature of the elementary excitations. For the comparison to semiconductors, we introduce effective models obtained from the Schrieffer-Wolff transformation, i.e. a strong-coupling expansion, which allows us to disentangle the different processes involved in the Hubbard model: intraband dynamics of doublons and holons, interband dipole excitations, and spin exchanges. These demonstrate the formal similarity of the Mott system to the semiconductor models in the dipole gauge, and reveal that the spin dynamics, which does not directly affect the charge dynamics, can reduce the HHG intensity. We also show that the long-range component of the intraband dipole moment has a substantial effect on the HHG intensity, while the correlated hopping terms for the doublons and holons essentially determine the shape of the HHG spectrum. A new numerical method to evaluate single-particle spectra within the iTEBD method is also introduced.

Carrier localization in quaternary Ga1−xMnxAs1−yPy ferromagnetic semiconductor films

Motivated by the fact that holes in the ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}\mathrm{As}$ family of ferromagnetic semiconductors play a key role in determining their ferromagnetic properties, we have measured hole concentrations in a series of three ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1--y}{\mathrm{P}}_{y}$ alloys grown by molecular beam epitaxy with varying amounts of phosphorus. This was carried out by Hall effect measurements, after eliminating the effect of the anomalous Hall term, and thus isolating the ordinary Hall term that directly provides the concentration of freely moving holes. Comparing these Hall effect results with total hole concentrations obtained from the number of acceptors and compensating donors as given by structural and magnetization measurements, we find that the number of itinerant holes (i.e., holes that contribute to the Hall effect) is significantly less than the total hole concentration. This indicates that a considerable fraction of the holes arising from Mn acceptors are localized. We find, furthermore, that the degree of such localization increases with the concentration of phosphorus in the ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}{\mathrm{As}}_{1--y}{\mathrm{P}}_{y}$ alloy. Our results indicate that the Curie temperature (and, by extension, other magnetic properties) described by the Zener model in ferromagnetic semiconductors of the ${\mathrm{Ga}}_{1--x}{\mathrm{Mn}}_{x}\mathrm{As}$ family are determined by the itinerant holes rather than by the total hole concentration. Finally, our results also indicate that ferromagnetism in these alloys vanishes when the total hole concentration falls below a certain Mott-like threshold, suggesting that the holes (both localized and itinerant) reside in the acceptor impurity band created by the presence of Mn acceptors.

Smooth Transonic Steady States of Hydrodynamic Model for Semiconductors

Related DatabasesWeb of Science You must be logged in with an active subscription to view this.Article DataHistorySubmitted: 1 February 2021Accepted: 01 June 2021Published online: 30 August 2021KeywordsEuler--Poisson equations, transonic solutions, hydrodynamic model of semiconductors, doping profileAMS Subject Headings35R35, 35Q35, 76N10, 35J70Publication DataISSN (print): 0036-1410ISSN (online): 1095-7154Publisher: Society for Industrial and Applied MathematicsCODEN: sjmaah

Multi-Objective Hierarchical Optimization: A Design Framework for Grid-Connected Interleaved H-Bridges

The paralleling of power converters connected to the grid for power-sharing is a widely used technique. In this context, the design framework for a low-cost, lightweight, compact and high-performance optimum configuration is an open problem. This paper proposes an innovative Multi-Objective Hierarchical Optimization Design Framework (MO-HO-DF) for an AC grid interface with $N$ interleaved H-bridges, each with $M$ parallel “to-be-determined” switches, connected through coupling inductances ( $L_f$ ). A total of eight figures of merit (FOMs) were identified for the design framework optimization. A rigorous model of the power electronic system is presented. Next, a highly computationally efficient algorithm for the estimation of the required frequency modulation ratio ( $m_f$ ) to meet current harmonic performance requirements for any given configuration is proposed. Then, the concept and implementation of the algorithm are presented for the MO-HO-DF. The effectiveness of the design optimization framework is demonstrated by comparing it to a base case solution. Finally, the design calculations are validated via PLECS simulation with manufacturer-provided 3D power semiconductor models that include thermal modelling.

Analysis of a New Implicit Solver for a Semiconductor Model

We present and analyze a new iterative solver for implicit discretizations of a simplified Boltzmann--Poisson system. The algorithm builds on recent work that incorporated a sweeping algorithm for ...

Nanoscale Degradation Models for Semiconductor, Dielectric and Oxide Parts in the Devices Included in Functional Systems in NPP

Nanoscale Degradation Models for Semiconductor, Dielectric and Oxide Parts in the Devices Included in Functional Systems in NPP

KDP-type crystal spontaneous polarization behavior better explained by bound charge semiconductor model than by mean field model

Mean-field models for behavior of ferroelectric (FE) crystals like KH2PO4 (KDP) succeed well in explaining behavior in the paraelectric (PE) phase in which the various phosphate groups HiPO4 (i = 1, 2, or 3) groups are distributed quite randomly. However, they underestimate the spontaneous polarization Ps in the FE phase, in which these groups are distributed quite nonrandomly. Instead, within the background of H2PO4 groups of either “all up” or “all down” polarity along the c axis, there are chains of nonpolar “Slater” H2PO4 groups with an H3PO4 “Takagi” group at one end and an HPO4 “Takagi” group at the other. Explained herein is the “bound charge semiconductor” model for the creation, growth, and interactions of such chains. It is then applied to show how these chains reduce Ps below the value it would have if all groups were H2PO4 groups of the same polarity. Comparison is made with the predictions of Ps for a mean field model.

Increasing power efficiency in the design of a low power and low phase noise CMOS LC oscillator

SummaryThis study developed a local oscillator (LO) with low phase noise and low power consumption. The proposed oscillator core comprises a pair of cross‐coupled transistors, which are fed by another pair of transistors that injects current at moments close to the peak of output voltage. The position of the current injection transistors, which are inserted in series with the cross‐coupled transistors, affects the waveform of current injected into an inductive–capacitive (LC) tank. Installing a capacitor on the source node of the cross‐coupled transistors increases the current injected into the LC tank and thereby augments the output voltage amplitude and power efficiency of the LO. The resonator phase shift and Q can be corrected by adjusting the source capacitance, which filters noise. These changes reduce the phase noise to −123.4 dBc/Hz at a frequency offset of 1 MHz and improve oscillator performance with a figure of merit equal to −193.5 dBc/Hz. To evaluate the LC tank, a 5 GHz LO was simulated at 1.8 V power supply and 2.5 mW power consumption. The simulation was conducted using a practical 0.18 complementary metal–oxide–semiconductor model manufactured by the Taiwan Semiconductor Manufacturing Company. The simulation results confirmed the analytical findings.