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Previous results indicated that acceptor doping was considered an effective clue to substantially suppress electronic thermal conductivity and in the meanwhile hold a rather low lattice thermal conductivity in high Yb-filled skutterudites. However, the strength of ionized impurity scattering needs to be regulated elaborately to balance the enhanced Seebeck coefficient and the deteriorated carrier mobility. In this work, Ge doping not only synergistically modulates the Fermi energy level and strength of ionized impurity scattering to an optimal range and attains a benign power factor but also offers a valuable opportunity to further suppress κe and κ in the classic Yb0.3Co4Sb12 alloy. Since the Yb0.3Co4Sb11.75Ge0.25 sample is endowed with the most highlighted ZT value in the device application temperature range, a promising average ZT value of 1.00 across the 300-823 K is achieved, reaching up to the level of a typical triple-filled skutterudite, which is highly desirable for achieving a satisfactory theoretical conversion efficiency of ∼14.5%. Our work corroborates that the ionized impurity strength is an extremely critical benchmark to obtain desirable thermoelectric performance in the high Yb-filled skutterudites.

InxGa1−xSe mixed crystals have been successfully grown from an indium flux by the traveling heater method at three growth temperatures. The thickness of the grown InxGa1−xSe mixed crystal perpendicular to (001) was more than 3 mm. The lattice constant, and optical and electrical properties of the InxGa1−xSe mixed crystals and undoped GaSe crystals were investigated and compared. The indium content of the InxGa1−xSe mixed crystals was observed to increase with decreasing growth temperature, while the lattice constant along the c-axis was observed to follow Vegard’s law. It was confirmed that a bandgap of In0.020Ga0.980Se is narrower than that of undoped GaSe according to the photoluminescence (PL) spectra. Compared with undoped GaSe crystal, the carrier concentration p was decreased by the incorporation of indium (In0.020Ga0.980Se, p = 6.4 × 1014 cm−3 at 257 K; In0.037Ga0.963Se, p = 2.6 × 1014 cm−3 at 257 K). In addition, it was suggested that the dominant carrier scattering mechanism of high-indium-content crystals at low temperature is ionized impurity scattering.

The widespread application of thermoelectric devices in cooling and waste heat recovery systems will be achieved when materials achieve high thermoelectric performance. However, improving thermoelectric performance is not straightforward because the Seebeck coefficient and electrical conductivity of the materials have opposite trends with varying carrier concentration. Here, we demonstrate that carrier scattering mechanism engineering can improve the power factor, which is the Seebeck coefficient squared multiplied by electrical conductivity, by significantly improving the electrical conductivity with a decreased Seebeck coefficient. The effect of engineering the carrier scattering mechanism was evaluated by comparing the band parameters (density-of-states effective mass, non-degenerate mobility) of Te-doped and Te, transition metal co-doped n-type Mg2Sb3 fitted via the single parabolic band model under different carrier scattering mechanisms. Previously, it was reported that co-doping transition metal with Te only changed the carrier scattering mechanism from ionized impurity scattering to mixed scattering between ionized impurities and acoustic phonons, compared to Te-doped samples. The approximately three times enhancement in the power factor of Te, transition metal co-doped samples reported in the literature have all been attributed to a change in the scattering mechanism. However, here it is demonstrated that Te, transition metal co-doping also increased the density-of-states effective mass. Here, the impact of the scattering mechanism change on the electric transport properties of n-type Mg2Sb3 without an effective mass increase was studied. Even without the effective mass increase, carrier scattering mechanism engineering improved the power factor, and its effect was maximized by appropriate carrier concentration tuning.

Recently, few-layer PtSe2 films have attracted significant attention due to their properties and promising applications in high-speed electronics, spintronics and optoelectronics. Until now, the transport properties of this material have not reached the theoretically predicted values, especially with regard to carrier mobility. In addition, it is not yet known which growth parameters (if any) can experimentally affect the carrier mobility value. This work presents the fabrication of horizontally aligned PtSe2 films using one-zone selenization of pre-deposited platinum layers. We have identified the Se : Pt ratio as a parameter controlling the charge carrier mobility in the thin films. The mobility increases more than twice as the ratio changes in a narrow interval around a value of 2. A simultaneous reduction of the carrier concentration suggests that ionized impurity scattering is responsible for the observed mobility behaviour. This significant finding may help to better understand the transport properties of few-layer PtSe2 films.

This work studies the effects of the temperature variation, from 300K to 500K, on the electrical parameters of SOI n-type and p-type junctionless nanowire transistors. The temperature influence on the threshold voltage, subthreshold slope, and the effective carrier mobility were analyzed. The mobility scattering mechanisms were analyzed and show that nanowire devices have the phonon scattering as their major component, although there is a significant component of the ionized impurity scattering that can be identified as well. These electrical parameters were also analyzed for short channel devices with a channel length of 40nm. P-type devices showed higher degradation with the temperature as the doping concentration is higher than n-type devices.

This work reports the electrical and thermal transport processes in p-type Pb-doped Mg3(1+x)Sb2−yPby (0.02 ≤ x ≤ 0.08; 0 ≤ y ≤ 0.02) compounds. Low-energy electron acceptor defects Mg vacancies are easy to form, which can provide holes and make p-type transport in the Mg3Sb2 matrix. However, with an increase in excess Mg, the transport behavior changes from p type to n type as manifested synergistically by both the Hall coefficient and Seebeck coefficient. This indicates the effective role of Mg in tuning carrier type and concentration for a pristine Mg3Sb2 compound. Upon substitution of Sb by Pb, the hole concentration slightly increases, and mobility is greatly improved by 133% at room temperature. The significant increase in mobility is attributed to the weakening ionized impurity scattering, stemming from the decreasing concentration induced by Pb doping. Thus, the power factor is enhanced with a 146% improvement at room temperature. Consequently, the figure of merit ZT of the Pb-doped sample is 1.8 times larger than the pristine one at around 300 K. Moreover, the non-degenerate transport behavior revealed by electrical properties is simply analyzed regarding the effects of minority carriers on the overall Seebeck coefficient. This study proposes a new strategy of charge compensation for improving mobility and a simple way to guide the prediction about the onset of bipolar conduction for Mg3Sb2-based compounds and other potential thermoelectric materials.

We present a first-principles framework to extract deformation potentials in silicon based on density-functional theory (DFT) and density-functional perturbation theory (DFPT). We compute the electronic band structures, phonon dispersion relations, and electron-phonon matrix elements to extract deformation potentials for acoustic and optical phonons for all possible processes. The matrix elements clearly show the separation between intra- and intervalley scattering in the conduction band, and quantify the strength of the scattering events in the degenerate bands of the valence band. We then use an advanced numerical Boltzmann transport equation (BTE) simulator that couples DFT electronic structures and energy/momentum-dependent scattering rates to compute the transport properties for electrons and holes. By incorporating ionized impurity scattering as well, we calculate the \ud n-type and p-type mobility versus carrier density and make comparisons to experiments, indicating excellent agreement. The fact that the method we present uses well-established theoretical tools and requires the extraction of only a limited number of matrix elements, makes it generally computationally very attractive, especially for semiconductors with a large unit cell and lower symmetry.

International audience; Single-crystalline Zn3N2 thin films have been grown on MgO (100) and YSZ (100) substrates by plasma-assisted molecular beam epitaxy. Depending on growth conditions, the film orientation can be tuned from (100) to (111). For each orientation, x-ray diffraction and reflection high-energy electron diffraction are used to determine the epitaxial relationships and to quantify the structural quality. Using high-temperature x-ray diffraction, the Zn3N2 linear thermal expansion coefficient is measured with an average of (1.5 ± 0.1) × 10−5 K−1 in the range of 300–700 K. The Zn3N2 films are found to be systematically n-type and degenerate, with carrier concentrations of 1019–1021 cm−3 and electron mobilities ranging from 4 to 388 cm2 V−1 s−1. Low-temperature Hall effect measurements show that ionized impurity scattering is the main mechanism limiting the mobility. The large carrier densities lead to measured optical bandgaps in the range of 1.05–1.37 eV due to Moss–Burstein band filling, with an extrapolated value of 0.99 eV for actual bandgap energy.

Using molecular beam epitaxy, we prepared seven p-type AlGaN samples of ~25% in Al content, including six samples with Mg-doped/un-doped AlGaN alternating-layer structures of different layer-thickness combinations, for comparing their p-type performances. Lower sheet resistance and higher effective hole mobility are obtained in a layer-structured sample, when compared with the reference sample of uniform Mg doping. The improved p-type performance in a layer-structured sample is attributed to the diffusion of holes generated in an Mg-doped layer into the neighboring un-doped layers, in which hole mobility is significantly higher because of weak ionized impurity scattering. Among the layer-structured samples, that of 6/4 nm in Mg-doped/un-doped thickness results in the lowest sheet resistance (the highest effective hole mobility), which is 4.83 times lower (4.57 times higher) when compared with the sample of uniform doping. The effects of the Mg-doped/un-doped layer structure on p-type performance in AlGaN and GaN are compared.

Three different Terahertz quantum-cascade-laser designs supporting clean n-level systems were analyzed using nonequilibrium Green’s functions. In clean n-level systems, most of the electrons occupy the active laser levels, with thermally activated leakage channels being suppressed almost entirely up to room temperature. Simulations of the three designs, namely a resonant phonon design, a two-well design, and a split-well direct-phonon design were investigated. The results from the simulations indicated that the two-well design would perform best overall, in terms of variations in current density, interface roughness, and ionized impurity scattering. We conclude that future research aiming to improve the temperature performance of such laser designs should be based on a two-well design.

Transparent p-CuI/n-SiZnSnO (SZTO) heterojunction diodes are successfully fabricated by thermal evaporation of a (111) oriented p-CuI polycrystalline film on top of an amorphous n-SZTO film grown by the RF magnetron sputtering method. A nitrogen annealing process reduces ionized impurity scattering dominantly incurred by Cu vacancy and structural defects at the grain boundaries in the CuI film to result in improved diode performance, the current rectification ratio estimated at ±2 V is enhanced from ≈106 to ≈107. Various diode parameters, including ideality factor, reverse saturation current, offset current, series resistance, and parallel resistance, are estimated based on the Shockley diode equation. An energy band diagram exhibiting the type-II band alignment is proposed to explain the diode characteristics. The present p-CuI/n-SZTO diode can be a promising building block for constructing useful optoelectronic components such as a light-emitting diode and a UV photodetector.

The kink effect, long observed in GaN high electron mobility transistors (HEMTs), is investigated with the Fermi kinetics transport hot electron simulation method. Fermi kinetics assigns piecewise Fermi-Dirac electron distributions to the conduction band valleys determined by the GaN electronic band structure and computes their behavior according to the thermodynamics of ideal Fermi gases. Charge fluxes are determined from moments of the Boltzmann equation, including nonparabolic electron densities of states and group velocities, as well as phonon and ionized impurity scattering. The model has been further generalized to include field-enhanced tunneling ionization of deep traps. Comparing simulations with measured data suggests that the kink effect could be caused by field-enhanced ionization of deep AlGaN barrier traps beneath the gate and close to the GaN/AlGaN interface. Further simulations indicate hot electrons may play key roles in both the trap emission and capture processes.

The resistivity of the undoped In0.53Ga0.47As photoconductive semiconductor switch has been measured over a temperature range of 5–300 K. The experimental temperature characteristic curve of the resistivity exhibits unimodality, and the peak resistivity is more than two orders of magnitude greater than that at 300 K. Based on the two-level model (shallow donor impurities level and deep defect level), we analyzed carrier relaxation rate due to scattering by ionized impurity and polar optical phonons. It is found that the unusually thermal characteristics is dominated by scattering of donor states by ionized impurity scattering and polar optical phonon scattering. The theoretical result is in very good agreement with the experimental results. Our results provide quantitative understanding of charge relaxation in InxGa1−xAs-based devices. Understanding of thermal properties of dark resistance can be used to optimize InxGa1−xAs-based electronic and photonic devices performance in different temperature regimes.

Although introducing more fillers in nanocages is beneficial to gain low lattice thermal conductivity within filling fraction limit, accompanying high electronic thermal conductivity usually results in an unsatisfactory figure of merit

An analytical solution has been found for the calculation of the Fermi level and the electrostatic screening factor for semiconductors and metal alloys in the degenerate limit using non-parabolic energy bands and Fermi statistics. The solution yields a more accurate determination of Fermi levels than methods that assume parabolic energy bands and a more accurate determination of screening factors than the Thomas–Fermi formula, which also assumes parabolic bands and thus predicts screening that is too weak relative to self-consistent field screening in highly degenerate systems, including metal alloys. Mobility and resistivity calculations using this analytical solution yield results that are closer to experimental data than traditional formulas derived assuming parabolic bands.

The high electron concentration and low mobility of ZnSnN2 hinder its potential applications in photocatalytic and optoelectronic devices. To reveal the mechanism, herein, ZnSnN2 thin films were prepared under different sputtering pressure. The results show that impurity band conduction, an electron density of above 1020cm−3 and a mobility of 2 cm2 V−1 s−1 dominated by variable-range hopping are observed in samples prepared at lower sputtering pressure, due to the unintentional incorporation of substitutional oxygen which is from residual vapour and which substitutes nitrogen, while conduction band conduction, an electron density of 1019 cm−3, a mobility of 24 cm2 V−1 s−1 limited by ionized impurity scattering and self-compensation ratio as well as an interband direct recombination emission are found in samples prepared at higher sputtering pressure, due to the decrease in substitutional oxygen doping.

Monolayer 2-D transition metal dichalcogenide (TMDC) field-effect transistors (FETs) have excellent scaling properties due to an extremely thin body and reduced quantum-mechanical tunneling. High-field and ballistic carrier transport can play an important role in aggressively scaled TMDC FETs. A compact model is developed to describe carrier transport in 2-D monolayer FETs based on a TMDC material. The model has the following features: 1) it treats high-field transport and velocity saturation; 2) it can be applied from ballistic to quasi-ballistic to diffusive transport regimes; and 3) it incorporates analytical expressions for carrier mobility values based on examining physical carrier scattering mechanisms in TMDC materials. Monte Carlo simulation, which solves the Boltzmann transport equation stochastically, is used to validate the model. The carrier transport model is further integrated with a virtual-source model to calculate the ${I}$ – ${V}$ characteristics of 2-D monolayer FETs. Based on the model, the effects of phonon scattering and ionized impurity scattering on the average carrier injection velocity and transistor ballisticity are discussed.

Diamond-like compounds represent a large family of new high-performance thermoelectric (TE) materials that have been extensively studied since 2009. However, their carrier mobilities are usually low because of the severe intrinsic lattice defects. In this study, we show a successful example of optimizing the carrier mobility of quaternary Cu2FeSnSe4 diamond-like compound by manipulating the intrinsic lattice defects. A series of Cu-rich Cu2+δFe1-δSnSe4 (δ = 0, 0.025, 0.05, 0.075, and 0.1) samples have been prepared in experiment. The rich Cu atoms effectively suppress the formation of negatively charged Cu vacancy defects, which are the main intrinsic lattice defects in Cu2FeSnSe4 according to the defect formation energy calculation. The reduction of Cu vacancy defects significantly weakens the ionized impurity scattering to the carriers, leading to the substantially increased carrier mobility and optimized electrical transport properties in these Cu-rich Cu2+δFe1-δSnSe4 samples. Consequently, the dimensionless figure of merit of Cu2.1Fe0.9SnSe4 at 800 K is enhanced by 53% as compared with that of the stoichiometric Cu2FeSnSe4. This study also sheds light on the optimization of TE performance in other materials with similar severe intrinsic lattice defects.

Relaxation processes and mobility of electrons in a semiconductor quantum well are studied. The modified Poschl-Teller potential is used as a confining potential. Scattering rates due to impurity ions, acoustic and piezoacoustic phonons are calculated taking into account the screening of scattering potentials by charge carriers. It is shown that when degenerate electrons are scattered by acoustic phonons, the dependence of scattering rate on electron wave number νac(k) is almost linear. At small k, the acoustic phonon piezoelectric scattering rate of degenerate electrons increases with k, and then it decreases slightly when k > 8 × 107 m−1. The ionized impurity scattering rate of degenerate electrons does not depend on temperature, is directly proportional to the electron density, and decreases with increasing k. Dependences of electron mobility on surface ion density and temperature are studied. It is shown that in the case of non-degenerate or slightly degenerate electron gas, a maximum appears in the temperature dependence of the mobility, and the screening effect is negligible. The screening significantly increases the mobility of electrons in the case of high degeneration. Obtained results are applied to GaAs-based quantum wells.

In this paper, we study the nonlinear channel electron mobility μ in an asymmetrically doped double quantum well field-effect transistor (QWFET) structure. The double quantum well consists of V-shaped channels by tailoring the conduction band edge of AlxGa1−xAs alloy through suitable variation of the alloy concentration x. We vary the widths of the wells asymmetrically and analyze their effect on the potential profile which causes drastic changes in the subband electron wave functions (ψn) and energy levels (En). In V-shaped potential, ψn are more localized than that of a square well. The change in the subband electronic structure induces change in occupation of subbands leading to intersubband interactions. We show that oscillatory enhancement in mobility under double subband can be obtained through the ionized impurity scattering through intersubband effects. The typical change of alloy concentration affects the alloy scattering which influences the overall total mobility μ.

Advanced functional materials 10, 2100258 (2021). doi:10.1002/adfm.202100258, Published by Wiley-VCH, Weinheim

In order to obtain excellent thermoelectric property of PbTe at room temperature, the most effective approach so far has been reducing the phonon thermal conductivity while maintaining the electronic performance. Based on the first-principles calculation, the scattering mechanisms of electrical transport and thermal transport are clarified. The electrical transport as well as thermal transport of PbTe under various mean free path are studied by taking into account electron/hole mean free path and phonon mean free path. The order of contribution to electrical transport is mean free path scattering>polar optical phonon scattering>acoustic deformation potential scattering>ionized impurity scattering. The Norma process dominates the three-phonon scattering channel, while the Umklapp process controls the four-phonon scattering channel. The 80% contribution of lattice thermal conductivity origins from acoustic branch, and the rest is from optical branch. When the hole/phonon mean free path is 10 nm, the ZT of p type is about 0.58, which is nearly four times larger than that of bulk ZT (0.15), implying the mean-free-path filtering is an effective method to enhance the value of ZT.

One big challenge of the emerging atomic precision advanced manufacturing (APAM) technology for microelectronics application is to realize APAM devices that operate at room temperature (RT). We demonstrate that semiclassical technology computer aided design (TCAD) device simulation tool can be employed to understand current leakage and improve APAM device design for RT operation. To establish the applicability of semiclassical simulation, we first show that a semiclassical impurity scattering model with the Fermi-Dirac statistics can explain the very low mobility in APAM devices quite well; we also show semiclassical TCAD reproduces measured sheet resistances when proper mobility values are used. We then apply semiclassical TCAD to simulate current leakage in realistic APAM wires. With insights from modeling, we were able to improve device design, fabricate Hall bars, and demonstrate RT operation for the very first time.

The chiral anomaly is one of the unusual effects of Weyl fermions and has attracted much interest. Experimental observation of this effect has largely been focused on a negative longitudinal magnetoresistance, which, however, has been proven to be insufficient. Thermoelectric experiment, a technique complimentary to the electrical resistivity and able to the capability to reveal the energy dependence of electron transport, has not been reported in many relevant semimetals. Here, we study the electrical and thermoelectric properties of a topological semimetal, $\mathrm{Zr}{\mathrm{Te}}_{5}$. Besides a previously reported negative magnetoresistance (NMR), a negative magnetothermopower (MTEP) is observed when the magnetic field is parallel to the temperature gradient. Both the magnetoconductivity and MTEP follow a quadratic dependence on the magnetic field. Moreover, the quadratic coefficient of MTEP is about twice as large as that of magnetoconductivity. These observations are consistent with the effect of the chiral anomaly. We also discuss other possible origins of these observations, such as current jetting, ionized impurity scattering, and spin-related effects.

Modulation doping has recently emerged as a method for improving the thermoelectric figure of merit using composite materials. By spatially decoupling charge carriers from their dopant impurities, the average carrier mobility can be improved by reducing the influence of ionized impurity scattering. However, as we show in the present work using a simple parabolic band model and effective medium approach, enhancement in such composites is effective only if ionized impurities dominate the scattering of the charge carriers, which is often not the case in many materials. For example, the enhancement is more significant at lower temperatures (T

The electronic structure and thermoelectric transport in SnSe and its alloy with Cu2Se have been studied using the first principles technique and semi classical Boltzmann transport theory. Our study reveals that SnSe is p-type with indirect band gap of 0.66 eV, while the alloy is phase separated and n-type with negligible indirect band gap of 0.064 eV. In both cases, two fold degeneracy in band extrema have been observed within the range of 25 meV. Delocalization of Se lone pair has been observed due to Cu substitution in Sn sites, which is supposed to lower its lattice thermal conductivity. A chemical potential map has been generated obeying thermodynamic restrictions to predict the possible existence of secondary phases. Our study shows the existence of SnSe2 as a secondary phase, while the possibility of Cu2Se as a secondary phase is negligible due to its higher formation energy. We calculated the transport coefficients as a function of carrier concentration and temperature to understand the range of optimized thermoelectric performance. The transport coefficients are similar along in plane direction whereas significant deviation is observed along the cross plane direction due to anisotropy in effective masses in SnSe. The effective masses are more isotropic in alloy than SnSe, thus transport properties show less anisotropy along three directions. Significant contribution of bipolar transport is observed in SnSe, while that is not noticed in the alloy. The behaviors of the Seebeck coefficients in both cases are discussed in terms of Mott's theory and density of states modification near Fermi energy. Electron mobilities limited by acoustic phonon, ionized impurities, alloy scattering and inter carrier scattering have been examined relying on deformation potential approach and effective mass theory. The results indicate that acoustic phonon scattering is dominant scattering mechanism in SnSe over inter carrier scattering, whereas for the alloy the former contribute very weakly. Ionized impurity scattering and inter carrier scattering are most dominant in the alloy. Alloy scattering with U = 2 eV also contribute significantly.

This work studies the effects of the temperature from 300K to 500K on the electrical parameters of SOI n-type junctionless nanowire transistors. The temperature influence on the threshold voltage and the effective carrier mobility were analyzed for narrow fin width. The mobility scattering mechanisms were analyzed and show that nanowire devices have the phonon scattering as it major component, although there is a significant component of the ionized impurity scattering that can be identified as well.

In this work we investigate crystal structure, morphology, and composition of CuI films produced in different modes of SILAR on glass plates and on flexible poly(ethylene terephthalate) (PET) substrates in connection with their transport properties, and with electrical and thermoelectric properties as a whole. Temperature dependences of resistivity for most CuI films have the crossover from semiconducting to metallic behavior with increasing temperature. The semiconductor carrier transport occurs in CuI films through nearest neighboring hopping. Metallic transport in CuI films carried out in accordance with the ionized impurity scattering and the carrier–carrier scattering model.

The semiclassical Boltzmann Transport Equation (BTE) is key in theoretical calculations of thermoelectric properties, both for electrons and phonons. The chapter will cover the physics of semiclassical transport methods (mainly the Boltzmann transport in the relaxation time approximation and briefly the Landauer approach). The chapter continues in deriving the thermoelectric coefficients from a circuit analysis point of view, and relates those to the BTE. Further on, it discusses the scattering physics of different scattering mechanisms for electronic transport, namely electron-phonon scattering, ionized impurity scattering, alloy scattering, and boundary scattering. Afterwards, the chapter presents a numerical scheme that allows for the consideration of the energy dependences of the scattering mechanisms coupled with arbitrary bandstructure shapes that characterize the new generation complex band thermoelectric materials. Such scheme can take the calculations beyond the simplistic constant relaxation time approximation within the BTE, and allow more accuracy in calculations, more design opportunities for high power factor material designs, as well as more reliable identification of promising thermoelectric materials through materials screening methods.

Mg3 (Sb,Bi)2 alloys have recently been discovered as a competitive alternative to the state-of-the-art n-type Bi2 (Te,Se)3 thermoelectric alloys. Previous theoretical studies predict that single crystals Mg3 (Sb,Bi)2 can exhibit higher thermoelectric performance near room temperature by eliminating grain boundary resistance. However, the intrinsic Mg defect chemistry makes it challenging to grow n-type Mg3 (Sb,Bi)2 single crystals. Here, the first thermoelectric properties of n-type Te-doped Mg3 Sb2 single crystals, synthesized by a combination of Sb-flux method and Mg-vapor annealing, is reported. The electrical conductivity and carrier mobility of single crystals exhibit a metallic behavior with a typical T-1.5 dependence, indicating that phonon scattering dominates the charge carrier transport. The absence of any evidence of ionized impurity scattering in Te-doped Mg3 Sb2 single crystals proves that the thermally activated mobility previously observed in polycrystalline materials is caused by grain boundary resistance. Eliminating this grain boundary resistance in the single crystals results in a large enhancement of the weighted mobility and figure of merit zT by more than 100% near room temperature. This work experimentally demonstrates the accurate understanding of charge-carrier scattering is crucial for developing high-performance thermoelectric materials and indicates that single-crystalline Mg3 (Sb,Bi)2 solid solutions can exhibit higher zT compared to polycrystalline samples.

N-type Mg 3 Sb 2- x Bi x alloys have been extensively studied in recent years due to their significantly enhanced thermoelectric figure of merit ( z T ), thus promoting them as potential candidates for waste heat recovery and cooling applications. In this review, the effects resulting from alloying Mg 3 Bi 2 with Mg 3 Sb 2 , including narrowed bandgap, decreased effective mass, and increased carrier mobility, are summarized. Subsequently, defect-controlled electrical properties in n-type Mg 3 Sb 2- x Bi x are revealed. On one hand, manipulation of intrinsic and extrinsic defects can achieve optimal carrier concentration. On the other hand, Mg vacancies dominate carrier-scattering mechanisms (ionized impurity scattering and grain boundary scattering). Both aspects are discussed for Mg 3 Sb 2- x Bi x thermoelectric materials. Finally, we review the present status of, and future outlook for, these materials in power generation and cooling applications.

We study the electrical transport properties of degenerate tin dioxide thin films with thickness larger than 250 nm. Our samples have a rutile structure and the effective mass of electron is 0.31 m0, which is obtained from the variation in optical bandgap. The temperature dependence of the Hall mobility indicates that the ionized impurity scattering is the dominant elastic scattering mechanism for electrons. In the low temperature range, the clear negative magnetoresistivity is observed, which can be attributed to the three-dimensional weak localization (WL) effect. By applying the three-dimensional WL theory, we extracted the electron dephasing length, which decreased on increasing temperature. Unexpectedly, the temperature dependence of the extracted dephasing length is found to be dominated by the electron-electron scattering in the small-energy-transfer process and the electron-phonon scattering has negligible contribution. This can be attributed to the low electron concentration in our samples.

The effect of the scattering-direction of hot electrons in the drain of ballistic \(n^{+}\)-\(i\)-\(n^{+}\) diodes is studied by a semi-classical Monte Carlo method. At low doping concentrations, the ionized impurity scattering has a weak influence on hot electron transport, although it is an elastic scattering. At sufficiently high doping concentrations on the other hand, the ionized impurity scattering enhances the backward flow of hot electrons, and severely degrades the peak of mean carrier-velocity in the channel and also the steady-state current. We argue that the scattering direction of hot electrons is the main reason behind these results.

*Özdemir, Mustafa D. ( Aksaray, Yazar ), The electronic transport characteristics of silicene sheets are studied by an Ensemble Monte Carlo (EMC) technique in the presence of phonon (acoustic, non-polar optic, surface polar optic), surface roughness and ionized impurity scattering mechanisms. Both intrinsic and silicene on an Al2O3 substrate are considered. Screening is also considered for both ionized impurity and surface polar optic phonon scattering of electrons. The velocity-applied field characteristics are obtained for both cases. A negative differential resistance (NDR) behaviour is observed for intrinsic case only. The mobility of carriers are calculated as a function of temperature for both cases and the results are compatible with existing experimental results and theoretical predictions. The effects of screening and flexural phonons on mobility are also studied.