载流子密度与散射时间的关系、高载流子密度屏蔽散射的数学关系及影响因素(二维材料中维度的影响)近期文献

… in time as a function of the excited carrier density. … -timedependent scattering potential W (t,t ) is simplified again using the GKBA. The electron density matrix and the effective scattering …

… by screening. Therefore, at low densities an increase of the carrier density makes more particles available for scattering but the matrix element for each scattering event is reduced. At …

A quantum model is developed to obtain electron capture and hot electron intraband relaxation times in a quantum well, for electron-longitudinal optic (LO) phonon scattering. In particular, we have investigated the effect of carrier density and electron energy, obtaining semi-analytic expressions as function of carrier density, a topic often neglected in literature, despite its fundamental interest in semiconductor physics. We demonstrated that the usual approximation of constant scattering time in modeling applications is often not adequate, because these parameters vary considerably with the injected or photogenerated carrier density. Furthermore we show that the scattering through the emission of pure LO-phonons is not a good approximation when the population increases, whereas the interplay between LO-phonon and collective plasma modes must be considered. We obtained novel semi-analytic expressions in the single plasmon pole dynamical form of the random phase approximation, without making use of the more usual static limit of it.

… of the peak bleaching is measured as a function of the injected carrier density at a fixed (-… insensitive to the density and dynamic screening effects. Carrier-carrier scattering (CCS) plays …

… time is about 150 fsec, relatively unaffected by electron energy or carrier density at our densities… that the screening of LO phonons that occurs at high carrier densities (& 10i cm …

… electron densities in the usual threedimensional metallic systems the scattering time is at … the modification of screening of an electron gas due to the presence of impurities, as discussed …

The electron transport properties of atomically thin semiconductors such as MoS2 have attracted significant recent scrutiny and controversy. In this work, the scattering mechanisms responsible for limiting the mobility of single layer semiconductors are evaluated. The roles of individual scattering rates are tracked as the 2D electron gas density is varied over orders of magnitude at various temperatures. From a comparative study of the individual scattering mechanisms, we conclude that all current reported values of mobilities in atomically thin transition-metal dichalcogenide semiconductors are limited by ionized impurity scattering. When the charged impurity densities are reduced, remote optical phonon scattering will determine the ceiling of the highest mobilities attainable in these ultrathin materials at room temperature. The intrinsic mobilities will be accessible only in clean suspended layers, as is also the case for graphene. Based on the study, we identify the best choices for surrounding dielectrics that will help attain the highest mobilities.

The electronic transport behaviour of materials determines their suitability for technological applications. We develop a computationally efficient method for calculating carrier scattering rates of solid-state semiconductors and insulators from first principles inputs. The present method extends existing polar and non-polar electron-phonon coupling, ionized impurity, and piezoelectric scattering mechanisms formulated for isotropic band structures to support highly anisotropic materials. We test the formalism by calculating the electronic transport properties of 23 semiconductors, including the large 48 atom CH3NH3PbI3 hybrid perovskite, and comparing the results against experimental measurements and more detailed scattering simulations. The Spearman rank coefficient of mobility against experiment (rs = 0.93) improves significantly on results obtained using a constant relaxation time approximation (rs = 0.52). We find our approach offers similar accuracy to state-of-the art methods at approximately 1/500th the computational cost, thus enabling its use in high-throughput computational workflows for the accurate screening of carrier mobilities, lifetimes, and thermoelectric power. It is difficult to compute the transport properties of a broad array of complex materials both accurately and inexpensively. Here, the authors develop a computationally efficient method for calculating carrier scattering rates of semiconductors, with good accuracy but low cost.

… between carriers, the carrier-carrier scattering time is … at different carrier densities indicate a screening behavior that reveals … The 2D screening that we deduce from the experiment iswell …

… carrier-carrier scattering at large densities, the spectra are completely structureless even at times … Even though the dependence of carrier-carrier scattering on the carrier density has …

… interface where, over the same chargedensity region, the two … -to-classical scattering time from competing scattering … the calculated screened-Coulomb scattering from residual charge …

… screening as indicated above, however, the density dependence of the screening will not be affected at early times … freehole density is proportional to the &ee electron density generated …

Monolayers of transition metal dichalcogenides (TMDC) have recently emerged as excellent platforms for exploiting new physics and applications relying on electronic valley degrees of freedom in two-dimensional (2D) systems. Here, we demonstrate that Coulomb screening by 2D carriers plays a critical role in excitonic valley pseudospin relaxation processes in naturally carrier-doped WSe2 monolayers (1L-WSe2). The exciton valley relaxation times were examined using polarization- and time-resolved photoluminescence spectroscopy at temperatures ranging from 10 to 160 K. We show that the temperature-dependent exciton valley relaxation times in 1L-WSe2 under various exciton and carrier densities can be understood using a unified framework of intervalley exciton scattering via momentum-dependent long-range electron–hole exchange interactions screened by 2D carriers that depend on the carrier density and the exciton linewidth. Moreover, the developed framework was successfully applied to engineer the valley polarization of excitons in 1L-WSe2. These findings may facilitate the development of TMDC-based opto-valleytronic devices. Atomically thin transition metal dichalcogenides offer a platform to explore the valley degree of freedom originating from their electronic band structure. Here, the authors use polarization- and time-resolved spectroscopy to investigate the temperature-dependent valley pseudospin relaxation processes in WSe2 monolayers.

The scattering of electrons with polar optical phonons (POP) is an important mechanism that limits electronic transport and determines electron mobility in polar materials. This is typically a stronger mechanism compared to nonpolar acoustic and optical phonon scattering and of similar strength to the Coulomb ionized impurity scattering. At high densities, on the other hand, the cloud of charge carriers screens the dipoles that are responsible for POP scattering and weakens the electron-POP scattering strength. However, in contrast to ionized impurity scattering, for which the well-known Brooks-Herring equation provides the scattering rates with the effect of screening included, for scattering with POP there is no such closed-form mathematical expression. In this work, we derive such an expression based on Fermi's golden rule, which would prove particularly useful in understanding electronic transport in complex crystal and complex band structure materials, in which electron-POP scattering could dominate electronic transport. Published by the American Physical Society 2025

We present a theoretical study of electron mobility in cylindrical gated silicon nanowires at 300 K based on the Kubo-Greenwood formula and the self-consistent solution of the Schrödinger and Poisson equations. A rigorous surface roughness scattering model is derived, which takes into account the roughness-induced fluctuation of the subband wave function, of the electron charge, and of the interface polarization charge. Dielectric screening of the scattering potential is modeled within the random phase approximation, wherein a generalized dielectric function for a multi-subband quasi-one-dimensional electron gas system is derived accounting for the presence of the gate electrode and the mismatch of the dielectric constant between the semiconductor and gate insulator. A nonparabolic correction method is also presented, which is applied to the calculation of the density of states, the matrix element of the scattering potential, and the generalized Lindhard function. The Coulomb scattering due to the fixed interface charge and the intra- and intervalley phonon scattering are included in the mobility calculation in addition to the surface roughness scattering. Using these models, we study the low-field electron mobility and its dependence on the silicon body diameter, effective field, dielectric constant, and gate insulator thickness.

… They attributed this to the disappearance of scattering centers. These findings are consistent with the present theory that the ion-pairing eliminates the original screened Coulomb fields …

We study the joint effect of disorder and Coulomb interaction screening on the exciton spectra in two-dimensional (2D) structures. These can be van der Waals structures or heterostructures of organic (polymeric) semiconductors as well as inorganic substances like transition metal dichalcogenides. We consider 2D screened hydrogenic problem with Rytova–Keldysh interaction by means of so-called fractional Scrödinger equation. Our main finding is that above synergy between screening and disorder either destroys the exciton (strong screening) or promote the creation of a bound state, leading to its collapse in the extreme case. Our second finding is energy levels crossing, i.e. the degeneracy (with respect to index μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu $$\end{document}) of the exciton eigenenergies at certain discrete value of screening radius. Latter effects may also be related to the quantum manifestations of chaotic exciton behavior in above 2D semiconductor structures. Hence, they should be considered in device applications, where the interplay between dielectric screening and disorder is important.

… two-dimensional systems.The purpose of this paper is to study screening effect and roles of chargedimpurity scattering… vanishing Coulomb matrix element for the backward scattering k ! …

Valuable insight into the influence of scattering from impurities on the peculiar electronic properties of graphene are gained by a systematic study of how its conductivity changes with increasing concentration of potassium ions deposited on its surface.

… on the mobility of 2D materials. On the one hand, the Coulomb scattering from the ions … density and therefore the screening of the impurity potential [13]. At gate voltages where charged …

… 2D compound forms of screened impurity potential are employed for the first time. In the framework of 2D … A significant suppression of the scattering rate τ − 1 (by an order of magnitude) …

… due to scattering by a single repulsive Coulomb impurity is … for carrier response and scattering reveals that the large … the Coulomb interaction, produces a nonlinear screening process …

Low temperature carrier transport properties in 2D semiconductor systems can be theoretically well-understood within RPA-Boltzmann theory as being limited by scattering from screened Coulomb disorder arising from random quenched charged impurities in the environment. In this work, we derive a number of analytical formula, supported by realistic numerical calculations, for the relevant density, mobility and temperature range where 2D transport should manifest strong intrinsic (i.e., arising purely from electronic effects) metallic temperature dependence in different semiconductor materials arising entirely from the 2D screening properties, thus providing an explanation for why the strong temperature dependence of the 2D resistivity can only be observed in high-quality and low-disorder 2D samples and also why some high-quality 2D materials manifest much weaker metallicity than other materials. We also discuss effects of interaction and disorder on the 2D screening properties in this context as well as compare 2D and 3D screening functions to comment why such a strong intrinsic temperature dependence arising from screening cannot occur in 3D metallic carrier transport. Experimentally verifiable predictions are made about the quantitative magnitude of the maximum possible low-temperature metallicity in 2D systems and the scaling behavior of the temperature scale controlling the quantum to classical crossover.

Atomic disorder is a common limiting factor for the low-temperature mobility in monolayer transition-metal dichalcogenides (TMDs; MX2). Here, we study the effect of often occurring atomic vacancies on carrier scattering and transport in p- and n-type monolayer MoS2. Due to charge trapping in vacancy-induced in-gap states, both neutral and charged vacancies resembling, respectively, short-range and combined short-range and long-range Coulomb scatterers, must be considered. Using the T-matrix formalism, we demonstrate a strong renormalization of the Born description of short-range scattering, manifested in a pronounced reduction and a characteristic energy dependence of the scattering rate. As a consequence, carrier scattering in TMDs with charged vacancies is dominated by the long-range Coulomb-disorder scattering, giving rise to a strong screening-induced temperature and density dependence of the low-temperature carrier mobility. For TMDs with neutral vacancies, the absence of intrinsic Coulomb disorder results in significantly higher mobilities as well as an unusual density dependence of the mobility which decreases with the carrier density. Our work illuminates the transport-limiting effects of atomic-vacancy scattering relevant for high-mobility TMD devices.

When atomically thin semiconducting transition metal dichalcogenides are used as a channel material, they are inevitably exposed to supporting substrates. This situation can lead to masking of intrinsic properties by undesired extrinsic doping and/or additional conductance fluctuations from the largely distributed Coulomb impurities at the interface between the channel and the substrate. Here, we report low-frequency noise characteristics in monolayer WS2 field-effect transistors on silicon/silicon-oxide substrate. To mitigate the effect of extrinsic low-frequency noise sources, a nitrogen annealing was carried out to provide better interface quality and to suppress the channel access resistance. The carrier number fluctuation and the correlated mobility fluctuation (CNF-CMF) model was better than the sole CNF one to explain our low-frequency noise data, because of the strong Coulomb scattering effect on the effective mobility caused by carrier trapping/detrapping at oxide traps. The temperature-dependent field-effect mobility in the four-probe configuration and the Coulomb scattering parameters are presented to support this strong Coulomb scattering effect on carrier transport in monolayer WS2 field-effect transistor.

A charged impurity outside the plane of a graphene layer contributes to scattering of electrons (and holes) in the graphene. The interaction occurs through two distinct mechanisms associated with the charge: (1) the (screened) Coulomb potential, and (2) the electric field perpendicular to the graphene plane that causes a spatially varying Rashba spin-orbit interaction. Both types of scattering are examined, with the screened potential self-consistently calculated in nonlinear Thomas-Fermi approximation. Different selection rules for the two mechanisms lead to qualitative differences in the differential scattering cross-sections. Using accepted parameters for the Rashba interaction, the latter is found to make only a very small contribution to the scattering associated with a remote charge.

… The implementation of dielectric functions based on the Random Phase Approximation (RPA), … This method yields the same dielectric function as the Mermin-corrected Lindhard and …

… (RPA)'dielectric functions based on realistic band-structure … ) calculation of dielectric functions involves no little labor. ' … paper the Thomas-Fermi (TF) theory" of dielectric screening in …

… the Thomas-Fermi (TF) and Random Phase Approximation (RPA) model. The four intrinsic and extrinsic phononic modes considered for electron-phonon scattering … ep relaxation rate in …

The nonequilibrium total dielectric function lends itself to a simple and general method for calculating the inelastic collision term in the electron Boltzmann equation for scattering from a coupled mode system. Useful applications include scattering from plasmon-polar phonon hybrid modes in modulation doped semiconductor structures. This paper presents numerical methods for including inelastic scattering at momentum-dependent hybrid phonon frequencies in the low-field Boltzmann equation for two-dimensional electrons coupled to bulk phonons. Results for electron mobility in GaAs show that the influence of mode coupling and dynamical screening on electron scattering from polar optical phonons is stronger for two dimensional electrons than was previously found for the three dimensional case.

… the calculation of impurity scattering rates in the investigation … the 2D-RPA much better than the Thomas-Fermi theory. … Now the Thomas–Fermi dielectric function is commonly defined as …

We theoretically investigate the influence of screening on electron-longitudinal optical phonon scattering in quantum cascade lasers. By employing ensemble Monte Carlo simulations, an advanced screening model based on the random-phase approximation is compared to the more elementary Thomas-Fermi and Debye models. For mid-infrared structures, and to a lesser extent also for terahertz designs, the inclusion of screening is shown to affect the simulated current and optical output power. Furthermore, it is demonstrated that by using the electron temperature rather than the lattice temperature, the Debye model can be significantly improved.

… approximation (RPA) dielectric functionand in the linearized ThomasFermi … and electron-impurity scattering rates, and shows how the phase-shift … RPA dielectric function were …

… the relaxation times, w and p. An inverse to the … concentration dependence of the momentum relaxation rate in the MOS inversion layer and in bulk silicon. The impurity concentration is …

… of momentum transfer contribute to relaxation time, for a given value of temperature and carrier density. … interactions in a superlattice make a significant contribution to relaxation time. …

At frequencies higher than 200–300 cm−1 in InP, the classical Drude theory fails to predict the observed wavelength dependence of the absorption coefficient and hence the optical conductivity to which it is proportional. In this paper, the optical conductivity is calculated for InP at 300 °K as a function of frequency and carrier concentration by use of a quantum extension of the Boltzmann transport equation which reduces to the quasiclassical Boltzmann equation in the limit of low frequencies and elastic scattering mechanisms. The conductivity is expressed in terms of a frequency-dependent relaxation time which reduces to a constant in the far infrared. It is given as a function of carrier concentration over the spectral region from 218 to 2180 cm−1 for carrier concentrations from 4.69×1015 to 2.13×1018 cm−3, and used to calculate the reflectivity spectrum over the same range of frequencies and concentrations. The low-frequency limit is used to estimate the dc mobility as a function of concentration, and the effect of compensation on mobility is calculated for the purest materials. Comparison with experimental results is given.

… effective relaxation time also increases at high electron … relaxation time increases at high fields. We have obtained the effective relaxation time for electrons as a function of the electron …

… Electron momentum relaxation time Using the formulas obtained for the function W(k ), we represent the components of the tensor of the reciprocal of the momentum relaxation time for …

AlGaN/GaN structures constitute a new class of 2D systems in that a large population of electrons can be produced without doping as a result of spontaneous and strain-induced polarization. Electron transport can, in principle, be mediated solely by phonon scattering and, for the first time, it is possible to realistically envisage the formation of a drifted Maxwellian or Fermi-Dirac distribution in hot-electron transport. We first describe a simple model that relates electron density in a heterostructure to barrier width and then explore electron-electron (e-e) energy and momentum exchange in some depth. We then illustrate the novel hot-electron transport properties that can arise when only phonon and e-e scattering are present. These include S-type NDR, electron cooling and squeezed electrons.

… In this paper we investigate the screening properties of a two-dimensional electron gas (2D … due to the Landauquantization the screening is highly nonlinear and strongly 8 dependent. …

… since level broadening in an electron gas has traditionally been … In this paper we calculate the two-dimensional … -temperature screening theory for a two-dimensional electron gas …

Electronic screening is a many-body phenomenon that strongly depends on the electron-electron interaction in an electron gas. Here, relaxing the assumption of “infinite and homogeneous background,” we show that the dielectric environment surrounding the electron gas alters the electron-electron interaction leading to substantial re-normalization of static and dynamic response of the electron gas. The re-normalization of static screening function by dielectric environment impacts experimentally measurable mobility as shown for Si-inversion layer for illustration. Results are analytical and can be used for accurate prediction of transport quantity for any two dimensional gas system with inhomogeneous dielectric environment.

Dielectric screening of excitons in 2D semiconductors is known to be a highly non-local effect, which in reciprocal space translates to a strong dependence on momentum transfer q. We present an analytical model dielectric function, including the full non-linear q-dependency, which may be used as an alternative to more numerically taxing ab initio screening functions. By verifying the good agreement between excitonic optical properties calculated using our model dielectric function, and those derived from ab initio methods, we demonstrate the versatility of this approach. Our test systems include: Monolayer hBN, monolayer MoS2, and the surface exciton of a 2 × 1 reconstructed Si(111) surface. Additionally, using our model, we easily take substrate screening effects into account. Hence, we include also a systematic study of the effects of substrate media on the excitonic optical properties of MoS2 and hBN.

… To find the expectation value of the one-particle two-dimensional density operator we multiplyby the Dirac density matrix p and take the trace. We find that the perturbation in the density …

… Using a combination of angle-dependent SE and polarization-dependent XAS at Ti L 3,2 and OK edges, we reveal that the enhancement of mobility is mainly caused by the increased …

… -2D systems are realized in the cases of electrons on the surface of liquid helium, electrons at … Concerning our study of screening transients in a 2D electron gas, an interesting feature is …

… symmetric Ve is not screened at all, because the only intervening polarization term in this approximation is P1 , corresponding to X1,1 and it is easily seen that in the limit Q→0, the Xn,n …

… In this work, the electronic transport properties in AlInGaN/AlN/InGaN/GaN double heterostructure (DH) are recalculated based on a modified Fang–Howard (FH) wave function [12] and …

… mobility for a GaAs single-interface heterolayer at low temperatures is computed, as a function of electron sheet density, in terms of the Fang-Howard-Stern model … of the screening of the …

We report on the calculation of the two dimension electron gas (2DEG) mobility in scaled AlGaN/GaN metal-insulator-semiconductor high-electron-mobility-transistors. We investigate the effect of remote impurity and phonon scattering models on the 2DEG mobility of the dielectric/AlGaN/GaN structure and investigate its variation with dielectric/AlGaN interface charge density, 2DEG concentration, and AlGaN thickness. Remote impurity scattering was found to be the dominant mechanism when the 2DEG density is below 5 × 1012 cm−2 and dielectric/AlGaN interface charge density is above 5 × 1012 cm−2. The interfacial charge has significant effect on the mobility as the AlGaN cap layer thickness is scaled down below 5 nm.

… analysis of the transport properties based on simplified assumptions of the one-band approximation, Fang-Howard wave function … The effect of screening has also been included [9]. …

We present a theoretical study the two-dimensional electron gas 2DEG at low temperature in an unintentionally doped GaN/AlGaN surface quantum well, taking adequate account of the roughness-induced scattering mechansms and effect due to sheet polarization charges. Within model of surface quantum wells 2DEG be described by an extended Fang-Howard wave function, we are able to derive an analytic expression for the self-consistent Hartree potential. Thus, we obtained simple expresion describing the enhancement of the 2DEG screening and unscreened\break potentials for different scattering sources. We studied the electron mobility due to different scattering sources and the total electron mobility in an unintentionally doped GaN/AlGaN surface quantum well.

We present a theoretical study the two-dimensional electron gas (2DEG) at low temperature in an unintentionally doped GaN/AlGaN surface quantum well, taking adequate account of the roughness-induced scattering mechansms and effect due to sheet polarization charges. Within model of surface quantum wells describes by an extended Fang-Howard wave function, we are able to derive an analytic expression for the self-consistent Hartree potential. Thus, we obtained simple expresion describing the enhancement of the 2DEG screening and unscreened potentials for different scattering sources. We studied the piezoelectric effect on the electron mobility in an unintentionally doped (UID) GaN/AlGaN surface quantum well.

… ground-state Fang–Howard wavefunction [26]. For simplicity it is assumed that screening is … dominant mechanism, which affects the transport properties of 2DEG at low temperatures. …

We have measured the alloy scattering of two-dimensionally (2D) confined electrons in AlxGa1−xAs in the dilute Al concentration limit. Alloy scattering is independent of temperature below 4.2 K, and from its linear dependence on the Al concentration we obtain a scattering rate of 35 ns−1 per 1% Al impurities. The alloy scattering potential determined from our data, using the Fang–Howard approximation of the wave function for the 2D electrons, is 1.13 eV.

Using high quality undoped GaAs/AlGaAs heterostructures with optically patterned insulation between two layers of gates, it is possible to investigate very low density mesoscopic regions where the number of impurities is well quantified. Signature appearances of the scattering length scale arise in confined two dimensional regions, where the zero-bias anomaly (ZBA) is also observed. These results explicitly outline the molecular beam epitaxy growth parameters necessary to obtain ultra low density large two dimensional regions as well as clean reproducible mesoscopic devices.

… of MoS 2 , described using a Fang–Howard formalism [28], … consider the effect of the screening of impurities by carriers … , and also for investigating transport in other alloy systems such …

Degradation of inversion layer electron mobility during Fowler–Nordheim electron injection has been investigated using n-channel metal-oxide-semiconductor transistors. The change of the reciprocal effective mobility, Δ(1/μEFF), has been found to be linearly related to the generated interface trap density, ΔNit, at a given effective electric field normal to the Si/SiO2 interface. The effect of trapped charges in the oxide on the mobility degradation is rather insignificant, which is attributed to the location of trapped charges from the Si/SiO2 interface. The dependence of mobility degradation on inversion layer electron density has also been explained using a transport theory based on two-dimensional electron gas.

Two-dimensional electron gas (2DEGs) could be tailored through the growth by LP-MOVPE of intentionally undoped AlGaN–GaN heterostructures with 6% < xAl < 36%. The carrier density (ns) is shown to be controlled by polarisation effects. Large carrier mobilities as high as 1710 cm2 V—1 s—1 at ns ∼ 9 × 1012 cm—2 can be measured at 300 K. For larger ns, the mobility drops first smoothly, then sharply when ns > 1.4 × 1013 cm—2. A two-subband model for 2DEG transport, taking into account phonons and impurity scattering mechanisms is proposed to explain semi-quantitatively the soft decay regime.

… In obtaining the electron mobilities to be discussed below, we have employed the multi-ion screening length rather than the conventional single-site result kp. However, the single-…

… electrons by the screened impurities and their contribution to the surface mobility. The Schrodingerequation for the envelope function in the presence of an impurity … a certain length 4. …

… The scattering of electrons by charged impurities in a semiconductor is conventionally seen as … For remoteimpurity scattering the length that enters the statistical weighting factor is not as …

… screening length exceeds the channel length. A remotely … of remote screening on ionized impurity scattering induced by the … This allows a scattering model to be calculated which can be …

… impurity scattering model which accounts for degenerate statistics, dispersive screening and two-ion scattering… s represents the inverse Thomas-Fermi screening length, F j denotes the …

We present a general theoretical treatment of ionized impurity scattering in semiconductor superlattices. Employing an extension of the quasi-two-dimensional calculations of Stern and Howard to multi-well structures, we explicitly account for nonuniformity of the wavefunction distribution function, arbitrary dispersion relations, scattering by impurities in neighboring periods, and screening by electrons in neighboring wells. Interperiod phenomena are found to be quite significant whenever the screening length is comparable to or longer than the distance between the quantum wells. Calculated results are compared with recent data for modulation-doped and setback-modulation-doped HgTe-CdTe superlattices. However, the discussion emphasizes general aspects of the problem rather than features specific to a particular system.

… random potential for charged-impurity scattering and the electron-electron interaction poten- … A is the height of the roughness and A is the length of the roughness fluctuations. This form …

… determines electronic structure and thus impurity screening. A … , the impurity level,8 the elastic scattering between conduction … The effective screening length () is further used to describe …

… disorder on the screening properties of a disordered electron gas use … impurity scattering, homogeneous background scattering, … 6 and A are the height and the length parameters of the …

… Electron mobility in GaAs due to ionized impurity scattering is calculated by considering nonlinear screening … (~) in the neighborhood of the screening length. The nonli. near potential is …

We calculate the mobility of carriers in a quantum well structure when they are scattered by ionized impurities in the size-quantum limit (SQL) where the carriers are assumed to populate only the lowest quantized energy level. It is found that the probability of scattering due to ionized impurities decreases with the well thickness in contrast to the case of acoustic phonon scattering where the scattering probability is enhanced under the conditions of the SQL. The temperature and thickness dependence of the mobility depends critically on the screening of the Coulomb potential due to the presence of the ionized impurities.

… Linear screening in strongly nonequilibrium semiconductors is studied by a Boltzmann-equation approach. In determining the nonequilibrium susceptibility χ (q, ω), the correct …

Author(s): Faghaninia, A; Ager, JW; Lo, CS | Abstract: © 2015 American Physical Society. Accurate models of carrier transport are essential for describing the electronic properties of semiconductor materials. To the best of our knowledge, the current models following the framework of the Boltzmann transport equation (BTE) either rely heavily on experimental data (i.e., semiempirical), or utilize simplifying assumptions, such as the constant relaxation time approximation (BTE-cRTA). While these models offer valuable physical insights and accurate calculations of transport properties in some cases, they often lack sufficient accuracy - particularly in capturing the correct trends with temperature and carrier concentration. We present here a transport model for calculating low-field electrical drift mobility and Seebeck coefficient of n-type semiconductors, by explicitly considering relevant physical phenomena (i.e., elastic and inelastic scattering mechanisms). We first rewrite expressions for the rates of elastic scattering mechanisms, in terms of ab initio properties, such as the band structure, density of states, and polar optical phonon frequency. We then solve the linear BTE to obtain the perturbation to the electron distribution - resulting from the dominant scattering mechanisms - and use this to calculate the overall mobility and Seebeck coefficient. Therefore, we have developed an ab initio model for calculating mobility and Seebeck coefficient using the Boltzmann transport (aMoBT) equation. Using aMoBT, we accurately calculate electrical transport properties of the compound n-type semiconductors, GaAs and InN, over various ranges of temperature and carrier concentration. aMoBT is fully predictive and provides high accuracy when compared to experimental measurements on both GaAs and InN, and vastly outperforms both semiempirical models and the BTE-cRTA. Therefore, we assert that this approach represents a first step towards a fully ab initio carrier transport model that is valid in all compound semiconductors.

… k'l =ko, where 2D is the screening length. Electronelectron collisions can be extremely strong … Since no rescaling of the potential has been done, this analysis allows typical values of the …

The theory of the screening of scattering fields by the carrier space charge for a semiconductor heterolayer (in which the electrons are confined in one direction, with discrete quantum levels, and mobile in the perpendicular plane), is developed on a general basis. The layer geometry makes the screening depend on functions of the normal-direction wave functions and the perpendicular Fourier wave vector. Applications, in particular for Ga–Al–As heterostructures, are made to the scattering between the two-dimensional Bloch states due to phonons and due to ions. For the phonons, moderate effects of screening on the mobility, in practical conditions, are found. For optical-mode phonons the plasma resonance at the lattice frequency can appreciably modify the scattering. For the ions, strong screening and correspondingly enhanced mobility is possible, in particular for modulation doping; the result for the mobility in the latter case is applied to recent experimental data. The ’’secondary screening’’ effects due to the polarizability of the normal-direction quantum states are analyzed and are found to be normally small.

… screening of the Coulomb interactions. In this connection we present a critical comparison between the generalized Boltzmann equations … for the screened Coulomb potential; although …

Two-dimensional materials can be strongly influenced by their surroundings. A dielectric environment screens and reduces the Coulomb interaction between electrons in the two-dimensional material. Since in Mott materials the Coulomb interaction is responsible for the insulating state, manipulating the dielectric screening provides direct control over Mottness. Our many-body calculations reveal the spectroscopic fingerprints of such Coulomb engineering: we demonstrate eV-scale changes to the position of the Hubbard bands and show a Coulomb engineered insulator-to-metal transition. Based on our proof-of-principle calculations, we discuss the (feasible) conditions under which our scenario of Coulomb engineering of Mott materials can be realized experimentally.

… of dielectric functions are the Thomas-Fermi model, random-phase approximation (RPA), … The Thomas-Fermi model is a static model representing a local screening charge density as …

… same calculation using Thomas-Fermi or RPA interactions. … An ab initio Eliashberg theory was developed to incorporate … dielectric function which was calculated in the Thomas-Fermi …

Plasmons are fundamental collective excitations in many particle charged systems like in free electron liquid in metals, high energy nuclear plasma in solar core or in fusion devices, in ion gas in ionosphere or in intra- and inter-galactic gas clouds. Plasmons play a central role also in small systems, in particular in metallic nanoparticles and in their arrays allowing for subdiffraction light manipulation. In analogy to metallic nanoparticles, we have developed description of the soft plasmonics in finite electrolyte systems confined in micrometer scale by insulating membranes. Plasmon-type excitations in such finite ionic systems are determined via originally formulated theoretical model allowing to describe surface and volume plasmons in confined geometry of the ion liquid. Size-effect for attenuation of surface plasmons in the finite electrolyte system is described and its various regimes are identified. The cross-over in the plasmon damping system-size-dependence is demonstrated including scattering of ions and their energy losses via irradiation. The plasmon resonances in ion systems replicate the metal cluster plasmon phenomena, though in distinct energy and size scale related to larger ion mass and lower ion concentration (in low energy plasma) in comparison to electrons in metals. The possibility for tuning plasmon resonances in finite ionic systems in a wide range by changing system size, ion, and electrolyte parameters is demonstrated.

We show that the rate for dark-matter-electron scattering in an arbitrary material is determined by an experimentally measurable quantity, the complex dielectric function, for any dark matter interaction that couples to electron density. This formulation automatically includes many-body effects, eliminates all systematic theoretical uncertainties on the electronic wave functions, and allows a direct calibration of the spectrum by electromagnetic probes such as infrared spectroscopy, x-ray scattering, and electron energy-loss spectroscopy. Our formalism applies for several common benchmark models, including spin-independent interactions through scalar and vector mediators of arbitrary mass. We discuss the consequences for standard semiconductor and superconductor targets and find that the true reach of superconductor detectors for light mediators exceeds previous estimates by several orders of magnitude, with further enhancements possible due to the low-energy tail of the plasmon. Using a heavy-fermion superconductor as an example, we show how our formulation allows a rapid and systematic investigation of novel electron scattering targets.

… Posterior calculations showed that the rate of capture into … provided by the Thomas-Fermi approximation to the RPA (dotted … The bulk dielectric function has been taken to be the RPA (…

Kinetic characteristics of the electron transport in a free-standing quantum well are studied theoretically. The quantization of acoustic phonons in a free-standing quantum well is taken into account and electron interactions with confined acoustic phonons through the deformation potential are treated rigorously. The kinetic equation for the electron distribution function is solved numerically for nondegenerate as well as degenerate electron gases and the electron momentum relaxation time and the electron mobility are obtained. At high lattice temperatures the electron momentum relaxation time is very similar to that obtained in the test particle approximation. Its dependence on the electron energy has steps which occur at the threshold energies for the dilatational phonons because an additional electron scattering by the corresponding acoustic phonon becomes important. The first mode makes the main contribution to the electron scattering, the contributions of the zeroth and the second modes are also important, the third and the higher modes practically unnoticeable for the studied electron concentrations and quantum well width. At lattice temperatures lower than the energy of the first dilatational acoustic mode the electron momentum relaxation time dependence on energy has additional peaks (in comparison with the test particle approximation) associated with electron scattering by several lowest acoustic phonon modes. These peaks occur near the Fermi energy in the degenerate case and in the energy range of the first dilatational modes in the nondegenerate case. They are especially pronounced for the degenerate electron gas. The temperature dependence of the electron mobility is similar to that described by the Bloch-Grüneisen formula, however we obtained a smaller negative exponent in the low temperature region.

We report on the development of a terahertz time-domain technique for measuring the momentum relaxation time of charge carriers in ultrathin semiconductor layers. Making use of the Drude model, our phase sensitive modulation technique directly provides the relaxation time. Time-resolved THz experiments were performed on n-doped GaAs and show precise agreement with data obtained by electrical characterization. The technique is well suited for studying novel materials where parameters such as the charge carriers' effective mass or the carrier density are not known a priori.

… Second, we measure the temperature dependence of the momentum relaxation time by four … relaxation time is approximately proportional to the inverse of the momentum relaxation time…

We present the studies of energy and momentum relaxation dynamics of nonequilibrium holes in GaxIn1−xNyAs1−y/GaAs quantum well modulation doped with Be. Experimental results show that the real-space transfer (RST) of hot holes occurs via thermionic emission from the high-mobility GaInNAs quantum wells into the low-mobility GaAs barriers at a threshold electric field of F∼6 kV/cm at T=13 K. At this field the hole drift velocity saturates at vd∼1×107 cm/s. A slight increase in the field above the threshold leads to the impact ionization of acceptors in the barriers by the nonequilibrium holes. We observe and model theoretically a negative differential mobility effect induced by RST that occurs at an electric field of F∼7 kV/cm. The observed current surge at electric fields above 7 kV/cm is attributed to the hole multiplication induced by shallow impurity breakdown in the GaAs barrier and impact ionization in the high-field domain regime associated with the packet of RST of holes in the well.

Terahertz time-domain conductivity measurements in 2 to 100 nm thick iron films resolve the femtosecond time delay between applied electric fields and resulting currents. This current response time decreases from 29 fs for thickest films to 7 fs for the thinnest films. The macroscopic response time is not strictly proportional to the conductivity. This excludes the existence of a single relaxation time universal for all conduction electrons. We must assume a distribution of microscopic momentum relaxation times. The macroscopic response time depends on average and variation of this distribution; the observed deviation between response time and conductivity scaling corresponds to the scaling of the variation. The variation of microscopic relaxation times depends on film thickness because electrons with different relaxation times are affected differently by the confinement since they have different mean free paths.

… equations for the carriers’ energy and momentum, are obtained quantities playing the role of time-dependent energy and momentum relaxation times. The electron drift velocity …

… the carrier mobility. An optical phonon energy of ħωLO=72 meV and momentum relaxation time … A dislocation density of Ndis=1.7×1012 cm–2 is estimated from comparison between …

Using time-resolved optical Kerr rotation, we measure the low temperature valley dynamics of resident electrons and holes in exfoliated WSe$_2$ monolayers as a systematic function of carrier density. In an effort to reconcile the many disparate timescales of carrier valley dynamics in monolayer semiconductors reported to date, we directly compare the doping-dependent valley relaxation in two electrostatically-gated WSe$_2$ monolayers having different dielectric environments. In a fully-encapsulated structure (hBN/WSe$_2$/hBN, where hBN is hexagonal boron nitride), valley relaxation is found to be monoexponential. The valley relaxation time $\tau_v$ is quite long ($\sim$10~$\mu$s) at low carrier densities, but decreases rapidly to less than 100~ns at high electron or hole densities $\gtrsim$2 $\times 10^{12}$~cm$^{-2}$. In contrast, in a partially-encapsulated WSe$_2$ monolayer placed directly on silicon dioxide (hBN/WSe$_2$/SiO$_2$), carrier valley relaxation is multi-exponential at low carrier densities. The difference is attributed to environmental disorder from the SiO$_2$ substrate. Unexpectedly, very small out-of-plane magnetic fields can increase $\tau_v$, especially in the hBN/WSe$_2$/SiO$_2$ structure, suggesting that localized states induced by disorder can play an important role in depolarizing spins and mediating the valley relaxation of resident carriers in monolayer transition metal-dichalcogenide semiconductors.

Excitation photon energy and carrier density dependence of spin dynamics in bulk CdTe crystal was studied by time resolved pump-probe reflectivity technique at room temperature. The results show that spin relaxation time decreases monotonously. While with increasing excitation carrier density, the time constants increases initially then decreases after reaching a maximum value. Our experimental results reveal that both D’yakonov–Perel’ [M. I. D’yakonov and V. I. Perel’, Sov. Phys. JETP 38, 177 (1974)] and Elliot–Yafet [R. J. Elliott, Phys. Rev. 96, 266 (1954); Y. Yafet, Solid State Phys. 14, 1 (1963)] mechanisms dominate the spin relaxation process in CdTe crystal.

… In this paper we present measurements which illustrate the effect of momentum relaxation of the photoexcited carriers on the electrical rise and fall times of the GaAs photoconductive …

We present a detailed experimental and theoretical analysis of the spin dynamics of two-dimensional electron gases (2DEGs) in a series of n-doped GaAs/AlxGa1?xAs quantum wells. Picosecond-resolution polarized pump-probe reflection techniques were applied in order to study in detail the temperature, concentration, and quantum-well-width dependencies of the spin relaxation rate of a small photoexcited electron population. A rapid enhancement of the spin lifetime with temperature up to a maximum near the Fermi temperature of the 2DEG was demonstrated experimentally. These observations are consistent with the D'yakonov-Perel' spin-relaxation mechanism controlled by electron-electron collisions. The experimental results and theoretical predictions for the spin relaxation times are in good quantitative agreement.

… and the mobility p - 7, (7, : momentum relaxation time). In this paper we present measurements of piezoresistance and energy relaxation time T< in a temperature range 30 zz T 5 300 K …

… Momentum-dependent and independent intraband … In this paper, we present both k-dependent and kindependent intraband relaxation time effects on nonMarkovian gain with many-…

… state properties of the 2D electron gas in the liquid and solid phases. … polarized liquid phases and for the crystal phase. Thisenables us to determine the density at which the electron gas …

The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO_3/(LaMnO_3)_1/SrMnO_3 heterostructure is predicted from density-functional calculations. The La(d) electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t_2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.

The formation of a two-dimensional electron gas at oxide interfaces as a consequence of polar discontinuities has generated an enormous amount of activity due to the variety of interesting effects it gives rise to. Here, we study under what circumstances similar processes can also take place underneath ferroelectric thin films. We use a simple Landau model to demonstrate that in the absence of extrinsic screening mechanisms, a monodomain phase can be stabilized in ferroelectric films by means of an electronic reconstruction. Unlike in the LaAlO3/SrTiO3 heterostructure, the emergence with thickness of the free charge at the interface is discontinuous. This prediction is confirmed by performing first-principles simulations of free-standing slabs of PbTiO3. The model is also used to predict the response of the system to an applied electric field, demonstrating that the two-dimensional electron gas can be switched on and off discontinuously and in a nonvolatile fashion. Furthermore, the reversal of the polarization can be used to switch between a two-dimensional electron gas and a two-dimensional hole gas, which should, in principle, have very different transport properties. We discuss the possible formation of polarization domains and how such configuration competes with the spontaneous accumulation of free charge at the interfaces.

… to the groundstate Fang-Howard wave function.For simplicity we assume that screening is … The transition from bulk to 2D transport is, therefore, very complex, but we believe that our …

&lt;div class="htmlview paragraph"&gt;Diesel engines are far more efficient than gasoline engines of comparable size, and emit less greenhouse gases that have been implicated in global warming. In 2000, the US EPA proposed very stringent emissions standards to be introduced in 2007 along with low sulfur (&amp;lt; 15 ppm) diesel fuel. The California Air Resource Board (CARB) has also established the principle that future diesel fueled vehicles should meet the same low emissions standards as gasoline fueled vehicles and the EPA followed suit with its Tier II emissions regulation. Achieving such low emissions cannot be done through engine development and fuel reformulation alone, and requires application of NOx and particulate matter (PM) aftertreatment control devices. There is a widespread consensus that NOx adsorbers and particulate filter are required in order for diesel engines to meet the 2007 emissions regulations for NOx and PM.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;In this paper, the key exhaust characteristics from an advanced diesel engine are reviewed. Development of the NOx adsorber technology is discussed. Spectroscopic techniques are applied to understand the underlying chemical reactions over the catalyst surface during NOx trapping and regeneration periods. In-situ surface probes are useful in providing not only thermodynamic and kinetics information required for model development but also a fundamental understanding of storage capacity and degradation mechanisms. The distribution of various nitration/sulfation species is related to surface basicity. Surface displacement reactions of carbonates also play roles in affecting the trapping capability of NOx adsorbers. When ultralow-S fuel is used as a reductant during the regeneration, sulfur induced performance degradation is still observed in an aged catalyst. Other possible sources related to catalyst deactivation include incomplete reduction of surface nitration, coke formation derived from incomplete hydrocarbon burning, and lubricant formulations. Sulfur management and the direction of future work for the successful implementation of such integrated engine and aftertreatment technology are discussed.&lt;/div&gt;

The electronic transport properties in AlGaN/AlN/GaN/AlGaN double heterostructures are investigated by an analytical model, considering the effect of the modified Fang-Howard wave function. The alloy disorder scattering is assumed to be eliminated by the introduction of an AlN insertion layer, and the rest five possible scattering mechanisms, acoustic deformation potential scattering, piezoelectric field scattering, polar optical phonons scattering, interface roughness scattering, and dislocation scattering, are taken into consideration in the calculation. The relations of two-dimensional electron gas (2DEG) density and mobility with alloy composition in the top AlGaN barrier layer and AlGaN buffer layer and the channel thickness are estimated and discussed. Finally, we compare the temperature dependences of the 2DEG mobility in Al0.25Ga0.75N/AlN/GaN/Al0.05Ga0.95N double heterostructures and in the conventional Al0.25Ga0.75N/AlN/GaN single heterostructures and explain them with detailed scattering processes.

… , particularly in electronic transport, appears to be in its infancy. In order to analyze the mobility, one must understand the scattering processes that dominate the mobility at different …

… , and employs the Fang–Howard approximation for the … of new regimes of electron transport, particularly in heterostructures. … Clearly, investigations of the transport properties of such a …

&lt;div class="htmlview paragraph"&gt;The use of biodiesel requires the development of proper quantification procedures for biodiesel content in blends and in lubricants (fuel dilution in oil). Although the ester carbonyl stretch at 1746 wavenumbers (cm&lt;sub&gt;-1&lt;/sub&gt;) is the most prominent band in the IR spectrum of biodiesel, it is difficult to use for quantification purposes due to a severe fluctuation of absorption strength from sample to sample, even at the same biodiesel content.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;We have demonstrated that the ester carbonyl fluctuation is not caused by variation in the ester alkyl chain length; but is most likely caused by the degree of hydrogen bonding of the ester functional group with water in the sample. Water molecules can form complexes with the ester compound affecting the strength of the ester carbonyl band. The impact of water on quantification of the biodiesel content of blends was significant, even for B100 samples that met the proposed ASTM D6751 water limit of 500 ppm by D6304 (Karl Fischer Methdod). By drying B100 and biodiesel blend samples, the relative standard deviation for the carbonyl band integrated intensity can be decreased five-fold, thus increasing the reliability of the method for quantification of biodiesel content.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;A phosphorus nuclear magnetic resonance (&lt;sup&gt;31&lt;/sup&gt;P-NMR) investigation revealed broadening in the bandwidth, due to interactions of the functional groups in zinc-dialkyldithiophosphate (ZDDP) with hydroxyl groups of hydroxy esters. Hydroxy esters serve as models of impurities in biodiesel (mono- or di-glycerides) or biodiesel partial oxidation products. Thus, biodiesel fuel dilution in lubrication oil may impact the antiwear properties of ZDDP through the formation of complexes with ZDDP that prevent the antiwear additives from forming a coating on the metal surface.&lt;/div&gt;

The introduction of AlGaN back-barrier increases the confinement of the two-dimensional electrons and further improves the high-frequency performance of AlGaN/AlN/GaN HEMTs. We …

… k is the electron de Broglie … scattering by neighboring ions is strictly valid only as long as the distance between ions is large compared to both the screening length X, and the electron …

… length. It is to answer these questions that we performed a theoretical study of the inelastic scattering rate for electron–electron scattering, … and the screened electron–electron interaction …

… phonon interaction, but nothing so far for the problem of the impurity scattering***. … Debye-Huckel potential and (10-1 is the Debye length. Thus again in the limit of the forward …

… scattering potential, even if it is screened by space charge to some extent. For most practical purposes, no exact treatment of ionized impurity scattering is … a convenient screening length; …

… than about the Debye-Huckol screening length the ionized impurities are … impurities are screened and have an arbitrary separation a so that they do not necessarily scatter the electrons …

… charge carriers to thefree-electron mass at rest and where k, … (This has been previously discussed at length by Fowler. ') … since once the ionized impurity's charge is screened or cut oG, …

… in the distribution function and the screening length. The calculation of the distribution … screening for ionized impurity scattering in degenerate semiconductors,” Solid-State Electron…

… on an effective potential. The bare Coulomb potential neglects screening of the intervening medium … Actually, the Boltzmann collision operator corresponds to using the bare Coulomb …

… expected for a converged transport calculation, which can be … for the band structure and deformation potentials of the electron-… Practically, the iteration convergence is checked for σαβ …

… Golden Rule with coupling factors obtained from deformation potential theory. Acoustic phonon scattering is also formulated in terms of deformation potentials[10]. Finally, we choose …

In this study the Green function solution of the Boltzmann transport equation on semiconducting thin film with irregular walls has been applied for the first time. The effects of electron …

… potential has several additional benefits. First, we wish to determine which screening length to use in the Boltzmann … the effective potential—electrononly screening, total DH screening, …

… weak dependence on the plasma density which appears in the Coulomb logarithm accounting for the screening of the Coulomb potential by space charge effects. Figure 3 shows the …

… At this midplane x̃ = 0, we define the zero reference of the potential Ṽ = 0, and because of the symmetry in eq 8, the potentials at both ends of the device will become opposite (equal to ± …

… applied to S N two dimensional transport equation in a rectangular domain considering … Planck (FP) equation, an alternative approach for the Boltzmann transport equation, assuming a …

We develop a framework of coupled transport equations for open heavy flavor and quarkonium states, in order to describe their transport inside the quark-gluon plasma. Our framework is capable of studying simultaneously both open and hidden heavy flavor observables in heavy-ion collision experiments and can account for both, uncorrelated and correlated recombination. Our recombination implementation depends on real-time open heavy quark and antiquark distributions. We carry out consistency tests to show how the interplay among open heavy flavor transport, quarkonium dissociation and recombination drives the system to equilibrium. We then apply our framework to study bottomonium production in heavy-ion collisions. We include ϒ(1S), ϒ(2S), ϒ(3S), χb(1P) and χb(2P) in the framework and take feed-down contributions during the hadronic gas stage into account. Cold nuclear matter effects are included by using nuclear parton distribution functions for the initial primordial heavy flavor production. A calibrated 2 + 1 dimensional viscous hydrodynamics is used to describe the bulk QCD medium. We calculate both the nuclear modification factor RAA of all bottomonia states and the azimuthal angular anisotropy coefficient v2 of the ϒ(1S) state and find that our results agree reasonably with experimental measurements. Our calculations indicate that correlated cross-talk recombination is an important production mechanism of bottomonium in current heavy-ion experiments. The importance of correlated recombination can be tested experimentally by measuring the ratio of RAA(χb(1P)) and RAA(ϒ(2S)).