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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.

Recently, owing to the excellent electrical and optical properties, n-type In2O3 nanowires (NWs) have attracted tremendous attention for application in memory devices, solar cells, and ultra-violet photodetectors. However, the relatively low electron mobility of In2O3 NWs grown by chemical vapor deposition (CVD) has limited their further utilization. In this study, utilizing in-situ Ga alloying, highly crystalline, uniform, and thin In2xGa2−2xO3 NWs with diameters down to 30 nm were successfully prepared via ambient-pressure CVD. Introducing an optimal amount of Ga (10 at.%) into the In2O3 lattice was found to effectively enhance the crystal quality and reduce the number of oxygen vacancies in the NWs. A further increase in the Ga concentration adversely induced the formation of a resistive β-Ga2O3 phase, thereby deteriorating the electrical properties of the NWs. Importantly, when configured into global back-gated NW field-effect transistors, the optimized In1.8Ga0.2O3 NWs exhibit significantly enhanced electron mobility reaching up to 750 cm2·V–1·s–1 as compared with that of the pure In2O3 NW, which can be attributed to the reduction in the number of oxygen vacancies and ionized impurity scattering centers. Highly ordered NW parallel arrayed devices were also fabricated to demonstrate the versatility and potency of these NWs for next-generation, large-scale, and high-performance nanoelectronics, sensors, etc.

We studied the temperature dependence (77–300 K) of the electron concentration and mobility using the Hall method under ultrasound (the acoustic Hall method) to determine the mechanisms by which ultrasound influences the electrical activity of near-dislocation clusters in n-type low-ohmic Cd1−xZnxTe single crystals (NCl ≈ 1024 m−3; x = 0; 0.04) with different dislocation density (0.4–5.1) × 1010 m−2. Changes in electrophysical parameters were found to occur as a function of temperature and ultrasound intensity. To evaluate the relative contribution of different charge carrier scattering mechanisms (lattice scattering, ionized impurity scattering, neutral impurity scattering, and dislocation scattering) and their change under ultrasound, a differential evolution method was used. This method made it possible to analyze experimental mobility μH(T) by its nonlinear approximation with characteristic temperature dependence for each mechanism. An increase in neutral impurity scattering and a decrease in ionized impurity and dislocation scattering components were observed under ultrasound. The character and the amount of these acoustically induced changes correlate with particular sample dislocation characteristics. It was concluded that the observed effects are related to the acoustically induced transformation of the point-defect structure, mainly in the near dislocation crystal regions.

We consider a finite, disordered 1D quantum lattice with a side-attached impurity. We study theoretically the transport of a single electron from the impurity into the lattice, at zero temperature. The transport is dominated by Anderson localization and, in general, the electron motion has a random character due to the lattice disorder. However, we show that by adjusting the impurity energy the electron can attain quasi-periodic motions, oscillating between the impurity and a small region of the lattice. This region corresponds to the center of a localized state in the lattice with an energy matched by that of the impurity. By precisely tuning the impurity energy, the electron can be set to oscillate between the impurity and a region far from the impurity, even distances larger than the Anderson localization length. The electron oscillations result from the interference of hybridized states, which have some resemblance to Pendry's necklace states [J. B. Pendry, J. Phys. C: Solid State Phys. 20, 733-742 (1987)]. The dependence of the electron motion on the impurity energy gives a potential mechanism for selectively routing an electron towards different regions of a 1D disordered lattice.

The effects of co-doping Na and Zn into thermoelectric Mg3Sb2 were investigated. Na was found to be a very effective hole dopant in our previous study. However, the lattice thermal conductivity noticeably increases limiting further improvement of the figure of merit. Here, we show that isoelectronic Zn doping weakens the polar covalent bonding and ionized impurity scattering and leads to a 3 fold increase of carrier mobility. Lattice thermal conductivity, due to the introduced ionic mass contrast between Zn2+ and Mg2+, is supressed significantly especially at lower temperature range between 300 K and 450 K. The indicator of the average performance, the (PF)eng (engineering power factor) and (ZT)eng (engineering ZT), were showed ∼50% and ∼76% improvement, respectively. The same strategy of co-doping two different elements with different functions could also be applied to other thermoelectric Zintl compounds typically with low carrier concentration and carrier mobility for even higher thermoelectric properties.

1T-type TiS2 has been recognized as a promising environmentally friendly thermoelectric material with a record ZT of around 0.4 so far. We hereby report the high thermoelectric performance of a series of TiS2–xAgSnSe2 composites with nano-AgSnSe2 as an ionized impurity for electron scattering. Electrical conductivities (σ) in the composites increased possibly due to intercalation; moreover, they showed an exceptional power law decay of σ ∝ Tm with m much increased in the temperature range of 400–580 K due to a significant contribution of ionized impurity scattering. Correspondingly, Seebeck coefficients (S) experience a much faster growth from ∼450 K to approach and even surpass that in pristine TiS2. The simultaneous enhancement of σ and S enabled a high power factor of ∼1.55 mW m−1 K−1 at 700 K. Besides, the lattice thermal conductivity was effectively reduced due to enhanced phonon scattering and intercalations, almost by half from 1.9 W m−1 K−1 to 1.0 W m−1 K−1 at 700 K. These synergistic effects renewed the record of ZT for TiS2-based thermoelectrics by almost doubling it to ∼0.8 at 700 K in the TiS2–4%AgSnSe2 composite.

In this work, we have investigated the effect of electric field and impurity position on nonlinear optical rectification of a double cone like quantum dot in the effective mass approximation and by using compact density-matrix formalism. We have calculated the energy levels and wave functions using finite element method (FEM) in the presence of impurity and influence of electric field. The results show that: (i) the binding energy changes with the impurity position and it is changed by the applied electric field, (ii) nonlinear optical rectification peak position of this system present the blue or red shift due to the applied electric field and changing the impurity position. (iii) for low electric field, impurity position plays an important role in electronic and optical properties, but for larger electric field, impurity position role becomes non-significant. (iv) the optical rectification changes due to the impurity position and the electric field are considerable.

The thermoelectric performance of InSb has been significantly improved via defect engineering or nanostructuring to reduce thermal conductivity in the past decade; however, less attention has been paid to improve its electrical properties via other key factors, e.g., carrier scattering mechanism, bipolar effect, etc. Here, we show that Bi doping on the Sb site not only significantly suppresses the high-temperature bipolar effect, but also leads to band convergence which enhances the Seebeck coefficient. As a result, a maximum zT of ∼0.43 @ 675 K is achieved in InSb0.97Bi0.03, which is increased by ∼43% as compared to that of pure InSb. In addition, the comparison of Bi and Ga doping (J. Mater. Chem., 2011, 21, 12398–12401) on the low-temperature electrical transport properties reveals that Bi doping is more beneficial for achieving high power factor due to the mixed acoustic phonon and ionized impurity scattering. Finally, it is suggested that Bi should be an effective dopant for electrical optimization of InSb and a further experiment on co-doping of Ga and Bi will be a considerable alternative for thermoelectric performance enhancement of InSb-based materials.

The electron mobility and the dark resistivity of undoped semi-insulating GaAs have been calculated theoretically over the temperature range from 5 to 500 K by taking into consideration all indispensable scattering processes, screening effects, and impurities compensation action. The two temperature characteristic curves of electron mobility and dark resistivity both exhibit unimodality. The peak value of the mobility as high as 11.4 × 105 cm2 V−1 s−1 can be achieved at 27 K, which is more than two orders of magnitude greater than that at 300 K. We analyzed the carrier relaxation rate due to scattering by ionized impurities, acoustic deformation potential, piezoelectric, and polar optical phonons. It is found that the unusually thermal characteristic is dominated by ionized impurity scattering, piezoelectric scattering, and polar optical phonon scattering in different temperature ranges, respectively. According to the scattering theory models, the dominant position relationships between the two different carrier scatterings induced by acoustical phonons in two-dimensional GaAs layer and bulk semi-insulating GaAs are discussed, respectively. The peak value of dark resistivity is about 1.29 × 1012 Ω cm at 154 K, which is more than five orders of magnitude greater than that at 300 K. The theoretical results are in good agreement with previously published results. Moreover, the dependence of the peak value of dark resistivity on the deep and shallow donor concentrations are obtained, respectively, and the mechanisms of the dependence are discussed. Understanding of thermal properties of dark resistivity and mobility can be used to optimize GaAs-based electronic and photonic devices’ performance in different temperature regimes.

The interplay of stress, disorder, and Coulomb screening dictating the mobility of doped cadmium oxide (CdO) is examined using Raman spectroscopy to identify the mechanisms driving dopant incorporation and scattering within this emerging infrared optical material. Specifically, multi-wavelength Raman and UV-vis spectroscopies are combined with electrical Hall measurements on a series of yttrium (X = Y) and indium (X = In) doped X:CdO thin-films. Hall measurements confirm n-type doping and establish carrier concentrations and mobilities. Spectral fitting along the low-frequency Raman combination bands, especially the TA+TO(X) mode, reveals that the evolution of strain and disorder within the lattice as a function of dopant concentration is strongly correlated with mobility. Coupling between the electronic and lattice environments was examined through analysis of first- and second-order longitudinal–optical phonon–plasmon coupled modes that monotonically decrease in energy and asymmetrically broaden with increasing dopant concentration. By fitting these trends to an impurity-induced Frohlich model for the Raman scattering intensity, exciton–phonon and exciton–impurity coupling factors are quantified. These coupling factors indicate a continual decrease in the amount of ionized impurity scattering with increasing dopant concentration and are not as well correlated with mobility. This shows that lattice strain and disorder are the primary determining factors for mobility in donor-doped CdO. In aggregate, the study confirms previously postulated defect equilibrium arguments for dopant incorporation in CdO while at the same time identifying paths for its further refinement.

This paper models the scattering limited electron transport in a nano-dimensional In 0 . 52 Al 0.48 As/In 0.53 Ga 0.47 As/InP heterostructure. An analytical model for temperature dependent sheet carrier concentration and carrier mobility in a two dimensional electron gas, confined in a triangular potential well has been developed. The model accounts for all the major scattering process including ionized impurity scattering and lattice scattering. Quantum mechanical variational technique is employed for studying the intrasubband scattering mechanism in the two dimensional electron gas. Results of various scattering limited structural parameters such as energy band-gap and functional parameters such as sheet carrier concentration, scattering rate and mobility are presented. The model corroborates the dominance of ionized impurity scattering mechanism at low temperatures and that of lattice scattering at high temperatures, both in turn limiting the carrier mobility. Net mobility obtained taking various scattering mechanisms into account has been found in agreement with earlier reported results, thus validating the model.

Electron and hole mobilities of GaN are calculated for three-dimensional (3D, bulk) and two-dimensional [2D, quantum well (QW), and HEMT] structures, including scattering processes of acoustic deformation potential, polar optical phonon, piezoelectric, ionized impurity, and so on. The calculated mobilities for 2D structures are strongly dependent on quantum well structures and impurity densities, although the temperature dependence of the mobilities behaves in a similar way to bulk values. In the present analysis, energy band structures of GaN are calculated by the empirical pseudopotential method including spin–orbit interaction, and then the electron effective mass of the conduction band and the hole effective masses of the valence bands are evaluated, which are used for the calculations of electron and hole mobilities. The calculated valence band structure of the heavy, light, and crystal field splitted valence bands reveal complicated dispersion due to the spin–orbit interaction. The obtained electron effective mass mc=0.145m is isotropic, and the heavy hole effective mass in the c∥ plane is mhh∥=1.20m, while in the c⊥ plane, the band edge effective mass is mhh0⊥=0.55m and the over all fitted heavy hole effective mass is mhh⊥=1.20m. The light hole effective masses are mlh∥=1.35m and mlh⊥=0.165m. Both of the electron and hole mobilities are limited by ionized impurity scattering at low temperatures and by polar optical phonon scattering at high temperatures. Calculated electron mobilities are 7100 cm2/Vs for bulk, 4600 cm2/Vs for high electron mobility transistor (HEMT), and 3600 cm2/Vs for QW at room temperature and calculated hole mobilities are 450 cm2/Vs for bulk, 450 cm2/Vs for HEMT, and 500 cm2/Vs for QW at room temperature. All the expressions for scattering rates and respective mobilities are derived for 3D and 2D (QW and HEMT) structures and enable readers to calculate electron and hole mobilities in different structures with parameters given in the table or modified ones.

Calculating the transport properties, such as electrical conductivity, has been a great challenge in materials modeling fields because of its complexity. We have implemented an algorithm to calculate the electronic transport properties using the generalized Kane band model and perturbation theory in the framework of the relaxation time approximation. Three scattering mechanisms affect the total relaxation time: acoustic phonon scattering, polar optical phonon scattering, and ionized impurity scattering. All the necessary parameters can be calculated from first principles . The capability of the program was tested on a group of semiconductors, and the obtained results show reasonable agreement with experiment. The program works fast, and is robust and especially appropriate for high-throughput screening of thermoelectric materials . Program summary Program title: AICON2 CPC Library link to program files: https://doi.org/10.17632/s9b8y8t92c.2 Code Ocean capsule: https://codeocean.com/capsule/7509547 Licensing provisions: GPLv3 Programming language: Python3 External routines/libraries: Numpy, Scipy, spglib, pymatgen, atomate, emc Nature of problem: Calculation of electrical and thermal conductivity from first principles requires a large number of computing resources in order to construct electron-phonon coupling matrix elements, integrate over the Brillouin zone and construct high-order force constants matrix. Solution method: Combining the perturbation theory with the deformation potential theory to calculate the electronic transport properties, using the modified Debye-Callaway model to calculate the phonon transport properties.

The electron mobility limited by different scattering mechanisms in the quaternary AlInGaN alloy grown on a GaN layer is investigated with the classical Hall measurement, which is performed at a temperature range of 12 and 350 K and a magnetic field of B = 0.51 T. The effect of the thickness and alloy composition of the quaternary AlInGaN layer on the mobility is also determined. The experimentally determined temperature-dependent Hall mobility was compared with mobility calculated by using Matthiessen's rule. The main scattering mechanisms, including acoustic phonon scattering (piezoelectric and deformation potential), polar optical phonon scattering, alloy disorder scattering, interface roughness scattering, ionized impurity scattering, dislocation scattering, background impurity scattering, were used in the calculations for all temperatures. The results show that the dominant scattering mechanisms, depending on the investigated sample, are the interface roughness scattering and alloy disorder scattering at almost all temperatures. At a low-temperature, mobility is limited by ionized impurity scattering. High-temperature mobility is limited by polar optical phonon scattering. Furthermore, our results suggest that the thickness and alloy composition of the quaternary AlInGaN layer should be optimized for better transport properties.

Influence of Al doping on the properties of band gap engineered Ca2+ substituted ZnO thin films were investigated. Al doped Zn0.85Ca0.15O films were prepared on glass substrates by spray pyrolysis technique and obtained lower resistivity (~ 10−3 Ωcm) and widened band gap. Films were polycrystalline and showed hexagonal wurtzite structure irrespective of doping. Due to the textured growth, crystallinity first improved and then decreased. Elemental analysis confirmed the incorporation of Ca and Al in ZnO lattice. Optical transmission in the visible and near infrared region varied in accordance with crystallinity and degradation at higher doping level is related to the scattering of photons by various disorders and to free carrier absorption. Optical energy gap increased with doping concentration due to Burstein-Moss effect as evident from Hall measurements. At higher doping level, carrier concentration and mobility decreased due to the limit of solid solubility and ionized impurity scattering respectively, but energy gap increased due to high polycrstallinity.

The possibility of implementing an off-resonant Raman scheme of optical quantum memory on the basis of an ensemble of three-level atoms is investigated under the condition of equal polarisations of resonant transitions forming the Λ-scheme. The developed model is used to analyse the signal-to-noise ratio at the output of an optical quantum memory device in 143Nd3+ : Y 7LiF4. It is shown that this ratio can significantly exceed unity for single-photon input pulses. The required values of the parameters can be obtained by using an impurity crystal in the form of a whispering-gallery mode ring resonator.

Achieving higher carrier mobility plays a pivotal role for obtaining potentially high thermoelectric performance. In principle, the carrier mobility is governed by the band structure as well as by the carrier scattering mechanism. Here, we demonstrate that by manipulating the carrier scattering mechanism in n-type Mg3Sb2-based materials, a substantial improvement in carrier mobility, and hence the power factor, can be achieved. In this work, Fe, Co, Hf, and Ta are doped on the Mg site of Mg3.2Sb1.5Bi0.49Te0.01, where the ionized impurity scattering crosses over to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼16 to ∼81 cm2⋅V-1⋅s-1 is obtained, thus leading to a notably enhanced power factor of ∼13 μW⋅cm-1⋅K-2 from ∼5 μW⋅cm-1⋅K-2 A simultaneous reduction in thermal conductivity is also achieved. Collectively, a figure of merit (ZT) of ∼1.7 is obtained at 773 K in Mg3.1Co0.1Sb1.5Bi0.49Te0.01 The concept of manipulating the carrier scattering mechanism to improve the mobility should also be applicable to other material systems.