Electron Transport In Semiconductors Research Articles

Вадим Євгенович Лашкарьов: багатогранний талант науковця і особистість

On 7 October 2023, the scientific community celebrated the 120th anniversary of the birth of Vadym Yevhenovych Lashkariov, a physicist, discoverer of the p-n junction, teacher, organiser of science, and simply a smart and decent person (07.10.2003 - 01.12.1974). In our opinion, the significance and influence of V.E. Lashkarev on the further development of physics, in particular semiconductor physics in Ukraine, has not been sufficiently revealed, although a number of articles have been published over the past decades on the life and scientific work of Vadym Yevhenovych. This article aims to look at the scientific work of Vadym Yevhenovych in the light of the newly emerging field of optoelectronics. The article shows some new aspects of the life and work of Academician of the National Academy of Sciences of Ukraine Vadym Yevhenovych Lashkariov, which are based on documents signed by him personally. Despite the blows of fate: exile and the Second World War, Vadym Yevhenovych retained his scientific inspiration and a far-sighted vision of the development of a new scientific field - semiconductor physics. The directions of the V. Lashkarev scientific school of semiconductor physics are analysed in details: studies of generation-recombination processes and electronic transport in semiconductors and semiconductor structures; theoretical and experimental studies of surface phenomena in semiconductors; theoretical and experimental studies of electronic transfer of two- dimensional free charge carriers in semiconductor nanostructures; studies of electrophysical and photoelectric effects in semiconductors and layered structures. Some examples of monographs and articles by students and followers of the V. Lashkarev scientific school, who developed the initial scientific fields and modernised the physics of semiconductors, are given.

Electron mobility of heavily doped semiconductors including multiple scattering by ionized impurities

A theoretical treatment of the multiple scattering problem for electrons in heavily doped semiconductors is developed for the purpose of resolving a long-standing discrepancy between theory and experiment on electron transport in semiconductors and semimetals. The scattering strength term in the traditional Brooks–Herring formula for ionized impurity scattering is modified to take into account the effect of the spatial proximity of ionized donors leading to an additional scattering term proportional to the cube of ionized impurity concentration, whereas the Brooks–Herring theory varies strictly linearly with the ionized impurity concentration. Comparisons between theory and experiment for GaAs, GaN, ZnO, and α-Sn are presented, showing significant improvement overall. In some cases, improvements greater than an order of magnitude are achieved. The agreement between theory and experiment for heavily doped ZnO over the temperature range of 21–322 K is within about 1%, depending on temperature.

Advanced Semiconductor Alloy Alxin1-Xp for Engineering and Medicine

Doped Advanced semiconductor materials with different properties are useful for early diagnosis and improved treatment in medical research. This is essential for advanced medical technology and lower mortality rates. New research on impurity-doped nano crystals is important. These dopants can directly affect electron transport in semiconductors, tune the optical properties of nano materials in desirable ways, and impart specific properties to the host. In this research report, we first discuss the factors that need to be considered to systematically control the production of these doped semiconductor materials, then describe various doped materials and typical synthetic approaches and techniques. Innovations in nanotechnology and materials design and their application in early diagnosis and treatment are believed to minimize the number of new cases of related diseases and reduce mortality.1,2,3 From natural to man-made materials, Doped semiconductor nanostructures, including inorganic and organic semiconductors, are increasingly attracting the attention of researchers and scientists worldwide

Stochastic Galerkin methods for the Boltzmann-Poisson system

We study uncertainty quantification for a Boltzmann-Poisson system that models electron transport in semiconductors and the physical collision mechanisms over the charges, using the stochastic Galerkin method in order to handle the randomness associated with the problem. In this study we choose first as a source of uncertainty the phonon energy, taking it as a random variable, as its value influences the energy jump appearing in the collision integral for electron-phonon scattering. Then we choose the lattice temperature as a random variable, since it defines the value of the collision operator terms in the case of electron-phonon scattering by being a parameter of the phonon distribution. Finally, we present our numerical simulations for the latter case. We calculate then with our stochastic Discontinuous Galerkin methods the uncertainty in kinetic moments such as density, mean energy, current, etc. associated to a possible physical temperature variation (assumed to follow a uniform distribution) in the lattice environment, as this uncertainty in the temperature is propagated into the electron PDF. Our mathematical and computational results let us predict then in a real world problem setting the impact that possible variations in the lab conditions (such as temperature) or limitations in the mathematical model (such as assumption of a constant phonon energy) will have over the uncertainty in the behavior of electronic devices.

Exact solution of electronic transport in semiconductors dominated by scattering on polaronic impurities

The scattering of electrons on impurities with internal degrees of freedom is bound to produce the signatures of the scatterer's own dynamics and results in nontrivial electronic transport properties. Previous studies of polaronic impurities in low-dimensional structures, like molecular junctions and one-dimensional nanowire models, have shown that perturbative treatments cannot account for a complex energy dependence of the scattering cross section in such systems. Here we derive the exact solution of polaronic impurities shaping the electronic transport in bulk (3D) systems. In the model with a short-ranged electron-phonon interaction, we solve for and sum over all elastic and inelastic partial cross sections, abundant in resonant features. The temperature dependence of the charge mobility shows the power-law dependence, $\mu(T)\propto T^{-\nu}$, with $\nu$ being highly sensitive to impurity parameters. The latter may explain nonuniversal power-law exponents observed experimentally, e.g. in high-quality organic molecular semiconductors.

Drift velocity in GaN semiconductors: Monte Carlo simulation and comparison with experimental measurements

Abstract Monte Carlo algorithms are developed to simulate the electron transport in semiconductors. In particular, the drift velocity in GaN semiconductors is calculated, and a comparison with experimental measurements is discussed. Explicit expressions for the scattering probabilities and distributions of the scattering angle of electrons on polar optical and intervalley phonons, and acoustic deformation potential as well are given. A good agreement of the simulation results and the experimental measurements reveals that the M-L valley is located at 0.7 eV higher than the Γ-valley. This value agrees with other experimental studies, while it is lower compared to ab initio calculations.

Large-time asymptotics for a matrix spin drift-diffusion model

The large-time asymptotics of the density matrix solving a drift-diffusion-Poisson model for the spin-polarized electron transport in semiconductors is proved. The equations are analyzed in a bounded domain with initial and Dirichlet boundary conditions. If the relaxation time is sufficiently small and the boundary data is close to the equilibrium state, the density matrix converges exponentially fast to the spinless near-equilibrium steady state. The proof is based on a reformulation of the matrix-valued cross-diffusion equations using spin-up and spin-down densities as well as the perpendicular component of the spin-vector density, which removes the cross-diffusion terms. Key elements of the proof are time-uniform positive lower and upper bounds for the spin-up and spin-down densities, derived from the De Giorgi–Moser iteration method, and estimates of the relative free energy for the spin-up and spin-down densities.

Understanding electronic transport in multi-component amorphous semiconductors

Amorphous semiconductors are an important class of semiconductors due to their low temperature deposition and high areal homogeneity over large areas which have been used mainly for display back panel driving circuits. Recent improvements in carrier mobilities in multi-component amorphous semiconductors have opened new area of applications for these amorphous semiconductors. To develop new multi component amorphous structures with optimized electronic properties, it is essential to understand the electron transport behavior in these materials. We have compared electronic structure of amorphous oxide and amorphous oxy-nitride semiconductors to understand the electronic transport in these semiconductors. We also propose certain methods to significantly reduce the computational time required to generate new multi-component amorphous structures and to study their electronic properties such that the development of new amorphous semiconductors with optimized electronic properties can be accelerated.

Assessment of Monte Carlo Simulation of Electron Transport in ZnO Diode in Intelligent Information Systems

Aim: The interest to study electron transport in semiconductor devices at very high electric field has been increased in the last decades and assessment of Monte Carlo simulation of electron transport in ZnO diode in intelligent information systems is of high significance. Method: The Monte Carlo method as applied to semiconductor transport is a simulation of the trajectories of individual Carriers as they move through a device under the influence of external forces and subject to random scattering events. Monte Carlo simulation is performed to study quasi-ballistic transport of electrons in n+nn+ ZnO diode. Result: In this simulation, the spatial motion of the electrons is semi classical and the scattering mechanisms taken into account are those due to acoustic phonons, non-polar optical phonons, polar optical phonons and ionized impurities. The simulation results are reported for different temperatures and voltages. Conclusion: It is also found that the transient properties of ZnO-made diode are not much sensitive to environment temperature changes, and thus the use of this substance is highly recommended in manufacture of electronic equipment.

Evaluating of Simulating the Transportation of Electron in Intelligent Information Systems and High-Tech Applicants

The interest to study electron transport in semiconductor devices at very high electric field has been increased in the last decades and assessment of Monte Carlo simulation of electron transport in ZnO diode in intelligent information systems is of high significance. The Monte Carlo method as applied to semiconductor transport is a simulation of the trajectories of individual Carriers as they move through a device under the influence of external forces and subject to random scattering events. Monte Carlo simulation is performed to study quasi-ballistic transport of electrons in n⁺nn⁺ ZnO diode. In this simulation, the spatial motion of the electrons is semi classical and the scattering mechanisms taken into account are those due to acoustic phonons, non-polar optical phonons, polar optical phonons and ionized impurities. The simulation results are reported for different temperatures and voltages. It is also found that the transient properties of ZnO-made diode are not much sensitive to environment temperature changes, and thus the use of this substance is highly recommended in manufacture of electronic equipment.

Modified Monte Carlo method for study of electron transport in degenerate electron gas in the presence of electron–electron interactions, application to graphene

Standard computational methods used to take account of the Pauli Exclusion Principle into Monte Carlo (MC) simulations of electron transport in semiconductors may give unphysical results in low field regime, where obtained electron distribution function takes values exceeding unity. Modified algorithms were already proposed and allow to correctly account for electron scattering on phonons or impurities. Present paper extends this approach and proposes improved simulation scheme allowing including Pauli exclusion principle for electron–electron (e–e) scattering into MC simulations. Simulations with significantly reduced computational cost recreate correct values of the electron distribution function. Proposed algorithm is applied to study transport properties of degenerate electrons in graphene with e–e interactions. This required adapting the treatment of e–e scattering in the case of linear band dispersion relation. Hence, this part of the simulation algorithm is described in details.

Global energy solutions to a stochastic Schrödinger–Poisson system with multiplicative noise in two dimensions

We are concerned with the Cauchy problem for a two-dimensional stochastic Schrödinger–Poisson system with a multiplicative noise in the energy space. Depending on the values of the physical parameters, this system models a self-gravitating Bose–Einstein condensate of the dark matter in the universe or the electron transport in semiconductors under the effect of thermal fluctuations. We show that in both cases the system admits a unique global solution in H1. The key ingredient of this paper is to establish appropriate commutator estimates for the multiplicative noise.

High-temperature stability of electron transport in semiconductors with strong spin-orbital interaction

Experimental results of the magnetotransport measurements (longitudinal magnetoresistance ${R}_{xx}$ and the Hall resistance ${R}_{xy}$) are presented over a wide interval of temperatures for several samples of ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Te}$ ($x\ensuremath{\approx}0.13--0.15$) grown by MBE---thin layers (thickness about 100 nm) strained and not strained and thick ones with thickness about $1\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$. An amazing temperature stability of the SdH-oscillation period and amplitude is observed in the entire temperature interval of measurements up to 50 K. Moreover, the quantum Hall effect (QHE) behavior of the Hall resistance is registered in the same temperature interval. These peculiarities of the ${R}_{xx}$ and ${R}_{xy}$ for strained thin layers are interpreted using quantum Hall conductivity (QHC) on topologically protected surface states (TPSS) [C. Br\une et al., Phys. Rev. Lett. 106, 126803 (2011)]. In the case of not strained layers it is assumed that the QHC on the TPSS (or on the resonant interface states) contributes also to the conductance of the bulk samples.

Distribution of impurity states and charge transport in Zr0.25Hf0.75Ni1+xSn1−ySby nanocomposites

Energy filtering of charge carriers in a semiconducting matrix using atomically coherent nanostructures can lead to a significant improvement of the thermoelectric figure of merit of the resulting composite. In this work, several half-Heusler/full-Heusler (HH/FH) nanocomposites with general compositions Zr0.25Hf0.75Ni1+xSn1−ySby (0≤x≤0.15 and y=0.005, 0.01 and 0.025) were synthesized in order to investigate the behavior of extrinsic carriers at the HH/FH interfaces. Electronic transport data showed that energy filtering of carriers at the HH/FH interfaces in Zr0.25Hf0.75Ni1+xSn1−ySby samples strongly depends on the doping level (y value) as well as the energy levels occupied by impurity states in the samples. For example, it was found that carrier filtering at HH/FH interfaces is negligible in Zr0.25Hf0.75Ni1+xSn1−ySby (y=0.01 and 0.025) composites where donor states originating from Sb dopant dominate electronic conduction. However, we observed a drastic decrease in the effective carrier density upon introduction of HH/FH interfaces for the mechanically alloyed Zr0.25Hf0.75Ni1+xSn0.995Sb0.005 samples where donor states from unintentional Fe impurities contribute the largest fraction of conduction electrons. This work demonstrates the ability to synergistically integrate the concepts of doping and energy filtering through nanostructuring for the optimization of electronic transport in semiconductors.

Elucidating the electron transport in semiconductors via Monte Carlo simulations: an inquiry-driven learning path for engineering undergraduates

Within the context of higher education for science or engineering undergraduates, we present an inquiry-driven learning path aimed at developing a more meaningful conceptual understanding of the electron dynamics in semiconductors in the presence of applied electric fields. The electron transport in a nondegenerate n-type indium phosphide bulk semiconductor is modelled using a multivalley Monte Carlo approach. The main characteristics of the electron dynamics are explored under different values of the driving electric field, lattice temperature and impurity density. Simulation results are presented by following a question-driven path of exploration, starting from the validation of the model and moving up to reasoned inquiries about the observed characteristics of electron dynamics. Our inquiry-driven learning path, based on numerical simulations, represents a viable example of how to integrate a traditional lecture-based teaching approach with effective learning strategies, providing science or engineering undergraduates with practical opportunities to enhance their comprehension of the physics governing the electron dynamics in semiconductors. Finally, we present a general discussion about the advantages and disadvantages of using an inquiry-based teaching approach within a learning environment based on semiconductor simulations.

Bounded weak solutions to a matrix drift–diffusion model for spin-coherent electron transport in semiconductors

The global-in-time existence and uniqueness of bounded weak solutions to a spinorial matrix drift–diffusion model for semiconductors is proved. Developing the electron density matrix in the Pauli basis, the coefficients (charge density and spin-vector density) satisfy a parabolic 4 × 4 cross-diffusion system. The key idea of the existence proof is to work with different variables: the spin-up and spin-down densities as well as the parallel and perpendicular components of the spin-vector density with respect to the precession vector. In these variables, the diffusion matrix becomes diagonal. The proofs of the L∞ estimates are based on Stampacchia truncation as well as Moser- and Alikakos-type iteration arguments. The monotonicity of the entropy (or free energy) is also proved. Numerical experiments in one-space dimension using a finite-volume discretization indicate that the entropy decays exponentially fast to the equilibrium state.

The intrinsic disorder related alloy scattering in ZrNiSn half-Heusler thermoelectric materials.

The intrinsic structural disorder dramatically affects the thermal and electronic transport in semiconductors. Although normally considered an ordered compound, the half-Heusler ZrNiSn displays many transport characteristics of a disordered alloy. Similar to the (Zr,Hf)NiSn based solid solutions, the unsubstituted ZrNiSn compound also exhibits charge transport dominated by alloy scattering, as demonstrated in this work. The unexpected charge transport, even in ZrNiSn which is normally considered fully ordered, can be explained by the Ni partially filling interstitial sites in this half-Heusler system. The influence of the disordering and defects in crystal structure on the electron transport process has also been quantitatively analyzed in ZrNiSn1-xSbx with carrier concentration nH ranging from 5.0×1019 to 2.3×1021 cm−3 by changing Sb dopant content. The optimized carrier concentration nH ≈ 3–4×1020 cm−2 results in ZT ≈ 0.8 at 875K. This work suggests that MNiSn (M = Hf, Zr, Ti) and perhaps most other half-Heusler thermoelectric materials should be considered highly disordered especially when trying to understand the electronic and phonon structure and transport features.

Enhanced Electron Transport in Nb-Doped TiO2 Nanoparticles via Pressure-Induced Phase Transitions

Anatase TiO2 is one of the most important energy materials but suffers from poor electrical conductivity. Nb doping has been considered as an effective way to improve its performance in the applications of photocatalysis, solar cells, Li batteries, and transparent conducting oxide films. Here, we report the further enhancement of electron transport in Nb-doped TiO2 nanoparticles via pressure-induced phase transitions. The phase transition behavior and influence of Nb doping in anatase Nb-TiO2 have been systematically investigated by in situ synchrotron X-ray diffraction and Raman spectroscopy. The bulk moduli are determined to be 179.5, 163.3, 148.3, and 139.0 GPa for 0, 2.5, 5.0, and 10.0 mol % Nb-doped TiO2, respectively. The Nb-concentration-dependent stiffness variation has been demonstrated: samples with higher Nb concentrations have lower stiffness. In situ resistance measurements reveal an increase of 40% in conductivity of quenched Nb-TiO2 in comparison to the pristine anatase phase. The pressure-induced conductivity evolution is discussed in detail in terms of the packing factor model, which provides direct evidence for the rationality of the correlation of packing factors with electron transport in semiconductors. Pressure-treated Nb-doped TiO2 with unique properties surpassing those in the anatase phase holds great promise for energy-related applications.

Monte Carlo Simulation of Ultrafast Carrier Transport: Scalability Study

In this work we consider Monte Carlo methods and algorithms for solving quantum-kinetic integral equations which describe the electron transport in semiconductors. Here we study the scalability of the presented algorithms using HPC resources in South-Eastern Europe. Numerical results for parallel efficiency and computational cost are also presented. In addition we discuss the coordinated use of heterogeneous HPC resources from one and the same application in order to achieve a good performance.

Some properties of the kinetic equation for electron transport in semiconductors

The paper studies the kinetic equation forelectron transport in semiconductors.New formulas for the heat generation rate are derivedby analyzing the basic scattering mechanisms.In addition, properties of thesteady state distribution are discussed and possibleextensions of the deviational particle Monte Carlo methodto the area of electron transport are proposed.