Acoustic Deformation Potential Research Articles

First principles investigation of electron mobility enhancement of β-Ga2O3 doped with indium.

β-Ga2O3 is one of the new-generation wide-bandgap semiconductor materials that has attracted much attention in recent years. However, the reported room-temperature electron mobility of β-Ga2O3 is much lower than GaN and SiC. Alloying Ga2O3 is expected to endow the material with superior carrier transport properties. Herein, we mainly investigate the electron mobility of pure Ga2O3, In-doped Ga2O3, and Al-doped Ga2O3 from first-principles considering acoustic deformation potential (ADP) scattering, polar optical phonon (POP) scattering and ionized impurity (IMP) scattering. The structure optimization, electronic band structure, and temperature-dependent and concentration-dependent electron mobility are investigated. The results show that the mobility of In-Ga2O3 is always the highest at 105-650 K, and POP scattering is the dominant factor limiting the electron mobility from 150-650 K. The mobility enhancement by In-doping is attributed to the smaller effective mass caused by the In 5s state despite its slightly increased electron-phonon coupling strength. The predicted electron mobilities for Ga2O3, Al-Ga2O3 and In-Ga2O3 at an electron concentration of 1.0 × 1017 cm-3 are 151.5 cm2 V-1 s-1, 137.8 cm2 V-1 s-1 and 184.9 cm2 V-1 s-1 at room temperature, respectively. This work provides an alternative route to enhance the electron mobility of Ga2O3 and guides in engineering their electronic transport properties for high-power electronics.

Tl2XY (X, Y = S, Se) monolayers with low lattice thermal conductivity and high thermoelectric performance by full-band approach with four scattering mechanisms

Abstract The low lattice thermal conductivity and high thermoelectric performance of the Janus Tl2SSe monolayer in the temperature region of 300–700 K are identified based on the thermoelectric properties of the Tl2S2, Tl2SSe, and Tl2Se2 monolayers. The transport coefficients for carrier concentrations and temperatures are obtained by solving the linearized Boltzmann transport equation in a full-band electronic structure. Four scattering mechanisms of acoustic deformation potential, optical deformation potential, polar optical phonon, and ionized impurity scatterings are considered. The ionized impurity scattering is recognized as the most important. The lattice thermal conductivity of the Janus Tl2SSe monolayer is substantially smaller than those of the Tl2S2, Tl2Se2 monolayers with higher symmetry. Moreover, we find that the Janus structures of the Tl2SSe monolayer increase the dielectronic constants and enhance the polar optical phonon scattering, then reduce the power factor to some extent. Therefore, the lattice thermal conductivity actually couples with the transport coefficient and cannot be individually regulated as is usually assumed. However, the ZT value of the Tl2SSe monolayer can still reach 1.77 at 700 K even if the intrinsic concentration and the bipolar effect are included. Therefore, the Tl2SSe monolayer is expected to be a promising candidate for thermoelectric materials.

Carrier scattering and temperature characteristics of mobility and resistivity of Fe-doped GaN

Abstract The electron mobility and dark resistivity of Fe-doped semi-insulating GaN (GaN:Fe) are calculated over the temperature range from 10 K to 500 K by considering the impurities compensation mechanism and majority carrier scattering. The temperature characteristic curve of the mobility exhibits unimodality and the curve of resistivity decreases monotonically with rising temperature. The carrier scatterings induced by ionized impurities, acoustic deformation potential, piezoelectric, and polar optical phonons are analyzed. It is found that the mobility is determined by ionized impurity scattering, piezoelectric scattering, and polar optical phonon scattering in different temperature ranges, and the contribution of acoustic deformation potential scattering is negligible over the entire temperature range. Furthermore, the effects of concentrations of shallow donors and deep acceptors on the temperature characteristic curves of mobility and resistivity, the peak mobility and its corresponding temperature (peak temperature), and the mobility and resistivity at room temperature are discussed. Our simulation shows the calculation results agree very well with the reported experimental and theoretical results when the Fe-related level is selected as 0.58 eV below the conduction band edge. Understanding of thermal properties of dark resistivity and mobility can be useful for optimizing GaN:Fe-based electronic and photonic devices performance in different temperature regimes.

Acoustic band engineering in terahertz quantum-cascade lasers and arbitrary superlattices

We present theoretical methods for the analysis of acoustic phonon modes in superlattice structures, and terahertz-frequency quantum-cascade lasers (THz QCLs). Our generalized numerical solution of the acoustic-wave equation provides good agreement with experimental pump-probe measurements of the acoustic resonances in a THz QCL. We predict that the detailed layer structure in THz QCLs imprints up to $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}$ detuning of the acoustic mode spacing, which cannot be seen in analytical models. This effect is strongest in devices with large and abrupt acoustic mismatch between layers. We use an acoustic deformation potential within a density-matrix approach to analyze electron transport induced in a range of the most common THz QCL active-region design schemes. We conclude that acoustic modes up to $\ensuremath{\sim}200\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}$ are capable of significantly perturbing QCL transport, highlighting their potential for ultrafast modulation of laser emission.

First-principles research on the thermoelectric properties of NbCoGe based on the scattering mechanisms

ABSTRACT Half-Heusler compounds have excellent power generation performance at high temperatures. The scattering mechanism is an essential factor affecting the electrical transport properties of thermoelectric materials. In computational simulations, only the role of acoustic phonon scattering on the thermoelectric properties of materials is considered, whereas other scattering mechanisms are neglected. In this work, we investigate the thermoelectric properties of NbCoGe compounds with different combinations of acoustic deformation potential, polar optical phonon, and ionised impurity scattering mechanisms. The calculated results show that the ZT values of n-type and p-type NbCoGe compounds reach 8 and 2.8, respectively, when only acoustic deformation potential scattering is considered, indicating that this sole scattering is insufficient. The calculated ZT values of p-type NbCoGe compounds reach 1.8 at 1200 K and more than 1 at 800 K for p- and n-type NbCoGe compounds under the combined effect of the three scattering mechanisms due to their high–power factor. This provides solid theoretical guidance for the search for potentially high–temperature half-Heusler thermoelectric materials.

The Transport phenomena in CdTe:Cl and CdTe:Cu - calculation from the first principles

In the presented article the method of determining the energy spectrum, the wave function of the charge carrier and the crystal potential in CdTe at an arbitrarily given temperature is considered. Using this approach within the framework of the supercell method the temperature dependences of the ionization energies of various types of defects caused by the introduction of chlorine and copper impurities in cadmium telluride are calculated. Also the offered method allows to define the temperature dependence of the optical and acoustic deformation potentials and as well as the dependence on the temperature the charge carrier’s scattering parameters on ionized impurities, polar optical, piezooptic and piezoacoustic phonons. Within the framework of short-range scattering models the temperature dependences of the charge carrier’s mobility and Hall factor are considered.

Velocity-field characteristics of MgxZn1−xO/ZnO heterostructures

In this work, electron transport in MgxZn1−xO/ZnO heterostructures at room temperature is simulated by the ensemble Monte Carlo (EMC) method. Electron scattering mechanisms including acoustic deformation potential, piezoelectric acoustic phonon, polar optical phonon (POP), interface roughness (IFR), dislocation, electron escape (ESC) and capture (CPR) by optical phonons, and random alloy are considered in EMC. The electron drift velocity in MgxZn1−xO/ZnO heterostructures is calculated for various Mg mole fractions x (0.1–0.3) at electric fields up to 25 kV/cm. We find that no obvious velocity saturation occurs in the range of the electric field considered. The results show that ESC scattering is one of the main physical mechanisms limiting the drift velocity. On the other hand, the competition between IFR and intersubband POP scattering is found to play an important role in the change in electron drift velocity with the increasing Mg mole fractions.

Comprehensive investigation of the extremely low lattice thermal conductivity and thermoelectric properties of BaIn2Te4

Recently, an extremely low lattice thermal conductivity value has been reported for the alkali-based telluride material ${\mathrm{BaIn}}_{2}{\mathrm{Te}}_{4}$. The value is comparable with low-thermal conductivity metal chalcogenides, and the glass limit is highly intriguing. Therefore, to shed light on this issue, we performed first-principles phonon thermal transport calculations. We predicted highly anisotropic lattice thermal conductivity along different directions via the solution of the linearized phonon Boltzmann transport equation. More importantly, we determined several different factors as the main sources of the predicted ultralow lattice thermal conductivity of this crystal, such as the strong interactions between low-frequency optical phonons and acoustic phonons, small phonon group velocities, and lattice anharmonicity indicated by large negative mode Gr\"uneisen parameters. Along with thermal transport calculations, we also investigated the electronic transport properties by accurately calculating the scattering mechanisms, namely the acoustic deformation potential, ionized impurity, and polar optical scatterings. The inclusion of spin-orbit coupling (SOC) for electronic structure is found to strongly affect the $p$-type Seebeck coefficients. Finally, we calculated the thermoelectric properties accurately, and the optimal $ZT$ value of $p$-type doping, which originated from high Seebeck coefficients, was predicted to exceed unity after 700 K and have a direction averaged value of 1.63 (1.76 in the $y$-direction) at 1000 K around $2\ifmmode\times\else\texttimes\fi{}{10}^{20}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ hole concentration. For $n$-type doping, a $ZT$ around $3.2\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ concentration was predicted to be a direction-averaged value of 1.40 (1.76 in the $z$-direction) at 1000 K, mostly originating from its high electron mobility. With the experimental evidence of high thermal stability, we showed that the ${\mathrm{BaIn}}_{2}{\mathrm{Te}}_{4}$ compound has the potential to be a promising mid- to high-temperature thermoelectric material for both $p$-type and $n$-type systems with appropriate doping.

Electron and Hole Mobility of SnO2 from Full-Band Electron–Phonon and Ionized Impurity Scattering Computations

Mobility is a key parameter for SnO2, which is extensively studied as a practical transparent oxide n-type semiconductor. In experiments, the mobility of electrons in bulk SnO2 single crystals varies from 70 to 260 cm2V−1s−1 at room temperature. Here, we calculate the mobility as limited by electron–phonon and ionized impurity scattering by coupling the Boltzmann transport equation with density functional theory electronic structures. The linearized Boltzmann transport equation is solved numerically beyond the commonly employed constant relaxation-time approximation by taking into account all energy and momentum dependencies of the scattering rates. Acoustic deformation potential and polar optical phonons are considered for electron–phonon scattering, where polar optical phonon scattering is found to be the main factor which determines the mobility of both electrons and holes at room temperature. The calculated phonon-limited electron mobility is found to be 265 cm2V−1s−1, whereas that of holes is found to be 7.6 cm2V−1s−1. We present the mobility as a function of the carrier concentration, which shows the upper mobility limit. The large difference between the mobilities of n-type and p-type SnO2 is a result of the different effective masses between electrons and holes.

Threading dislocation lines and their impact on bulk cubic boron nitride’s low-field electron transport response

Building upon Chilleri et al.’s [Solid State Commun. 352 (2022) 114776] relaxation-time approximation based low-field electron drift mobility formalism, we incorporate treatment of threading dislocation related scattering into this analytical framework. Then, for a reasonable range of threading dislocation line density selections, representative of boron nitride’s zinc-blende phase, the role that threading dislocation lines play in shaping the low-field electron transport response of this material is examined. The six scattering processes considered in this analysis include the ionized impurity, polar optical phonon, acoustic deformation potential, piezoelectric, inter-valley, and threading dislocation line related scattering processes. The impact of threading dislocations is assessed through evaluations of the scattering rates, the fractional scattering contributions, and the low-field electron drift mobility contributions associated with the various scattering processes. The dependence of the total low-field electron drift mobility on the threading dislocation line density is also examined. We conclude the analysis with a comparison with the results of experiment. Threading dislocation lines are found to be a significant contributor to bulk zinc-blende boron nitride’s low-field electron transport response.

Effect of diffusion on acoustic deformation potential characterization through coherent acoustic phonon dynamics

Ultrafast spectroscopy of coherent acoustic phonon (CAP) dynamics has recently been proposed as a method to characterize acoustic deformation potential (ADP), a key standard to quantify carrier--acoustic phonon coupling in semiconductors. In this Letter, we illustrate the importance of addressing the diffusion effect in ADP characterization by this method, using Ge as the demonstration system. It is found that the ADP mechanism and the thermoelastic effect have comparable contributions to CAP generation in Ge. Due to the different dependences on pump photon energies, the roles of these two mechanisms were assessed by varying pump wavelengths, based on which the ADP coupling constant of Ge was obtained. The analysis reveals that the carrier diffusion has a considerable impact on the shape of the CAP wave packet and must be processed cautiously for the ADP characterization for Ge.

Determination of the acoustic phonon deformation potentials in diamond

The interaction between acoustic phonons and electrons in diamond has been investigated by comparing state-of-the-art time-of-flight drift velocity measurements with Monte Carlo simulations. We use a multivariable anisotropic description of acoustic deformation potential scattering. The phonon-electron interaction is the limiting factor for the carrier mobility in ultrapure single crystal diamond. Hence, having a correct description is necessary for both device simulations and for predicting the maximum device performance. The experiments were performed at low temperature and using ultrapure diamond to minimize the influence of other scattering sources. The electronic valley polarization in diamond at low temperatures enables determination of both uniaxial and dilatation deformation potentials in the same experiment. The uniaxial and dilatation deformation potentials are found to be $18.5\ifmmode\pm\else\textpm\fi{}0.2$ and $\ensuremath{-}5.7\ifmmode\pm\else\textpm\fi{}0.3$ eV, respectively.

Transport phenomena in copper doped cadmium telluride: calculation from the first principles

In the presented work, the method of determining the energy spectrum, the wave function of the heavy hole and the crystal potential in CdTe at an arbitrarily given temperature is considered. Using this approach within the framework of the supercell method the temperature dependences of the ionization energies of various types of defects caused by the introduction of copper impurity in cadmium telluride are calculated. Also the proposed method makes it possible to define the temperature dependence of the optical and acoustic deformation potentials, as well as the temperature dependence of the scattering parameters of heavy holes on ionized impurities, polar optical, piezooptical and piezoacoustic phonons. Within the framework of short-range scattering models, the temperature dependences of the heavy hole mobility and Hall factor are considered.

Theoretical prediction of mechanics, transport, and thermoelectric properties of full Heusler compounds Na2KSb and X2CsSb (X=K,Rb)

Full Heusler compounds have become a research hotspot in the thermoelectric (TE) field, because they have the remarkable electronic properties and high-TE power factor. Nevertheless, the inherent high thermal conductivity ${\ensuremath{\kappa}}_{L}$ hinders their further application as TE device. Hence, we investigate the mechanical, transport, and thermoelectric properties in ${\mathrm{Na}}_{2}\mathrm{KSb}$ and ${\mathrm{X}}_{2}\mathrm{CsSb}$ (X = K, Rb) with eight valence electrons per formula unit (f.u.) by using the first-principles calculations combined with self-consistent phonon (SCP) theory, compressive sensing (CS) techniques, and Boltzmann transport equation (BTE). Due to the strong three phonon scattering combined with small phonon group velocity, we obtain the ultralow lattice thermal conductivities. An evaluation of their mechanical properties reveals that they are all brittle compounds, and ${\mathrm{Rb}}_{2}\mathrm{CsSb}$ has the strongest elastic anisotropy. To capture rational electron transport properties, we include the effects of the acoustic deformation potential (ADP) scattering, polar optical phonon (POP) scattering, and ionized impurity (IMP) scattering on the electron relaxation time. Finally, a high p-type $\mathit{ZT}$ values of 2.74 (2.48) at 600 (900) K are captured in the cubic ${\mathrm{K}}_{2}\mathrm{CsSb}$ $({\mathrm{Na}}_{2}\mathrm{KSb})$. These findings not only help us to comprehensively understand the physical properties of full Heusler compounds with eight valence electrons per f.u., but also support them as potential candidates for thermal management and thermoelectric applications.

A low-field electron mobility analysis of cubic boron nitride

We examine zinc-blende boron nitride’s low-field electron transport response. In particular, within the framework of a relaxation-time approximation analysis, we probe how the individual scattering processes contribute to the total electron drift mobility. The scattering processes considered include the ionized impurity, polar optical phonon, acoustic deformation potential, piezoelectric, and inter-valley scattering processes. A comparison with the results of experiment is presented.

Heavy hole scattering on intrinsic acceptor defects in cadmium telluride: calculation from the first principles

In the present paper the way to describe the energy spectrum, the wave function and self- consistent potential in a semiconductor with a sphalerite structure at a predetermined temperature is proposed. Using this approach within the framework of the supercell method the temperature dependences of the ionization energy of intrinsic acceptor defects in cadmium telluride are calculated. In addition, on the basis of this method, the temperature dependences of the heavy holes effective mass, optical and acoustic deformation potentials, as well as of the heavy holes scattering parameters on ionized impurities, polar optical, piezooptic and piezoacoustic phonons were established. Within the framework of short-range scattering models the temperature dependences of the heavy hole mobility and Hall factor in CdTe crystals with defects concentrations 5´*1022 - 5*´1024 cm-3 are considered.

Observation of photo-induced plasmon-phonon coupling in PbTe via ultrafast x-ray scattering.

We report the observation of photo-induced plasmon–phonon coupled modes in the group IV–VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.

The carrier mobility and sizable bandgap influorinated armchair boron nitride nanoribbons

The electronic transport properties of two-dimensional materials are strongly influenced by the charge carrier mobility and the energy bandgap. Furthermore, the carrier-phonon interaction governs the electrical response of any electrical device at a specific temperature. In light of this, the electron mobility and energy bandgap of fluorine (F) doped armchair Boron Nitride nanoribbons (a-BNNRs) are computed theoretically and analysed further. The acoustical deformation potential (ADP) scattering mechanism is taken into account to determine the mobility of the system. The calculations are carried out in presence of an applied electric field as well as different doping concentrations across a specified temperature range (200–300 K). The computed value of electron mobility for F-BNNR is of the order 104 cm2 V−1 s−1. Such higher magnitude of electron mobility suggests the semiconducting nature of BNNRs. Moreover, the variation of electron mobility as a function of temperature and doping concentration demonstrates a significant reduction in the acoustical phonon-limited electron mobility of fluorine-doped boron nitride nanoribbons. To estimate the energy bandgap, a set of equations are determined from the Fermi velocity expression using the nearly free electron (NFE) model. The computed energy bandgap is found to diminish with the increasing size of the nanoribbon. This behaviour of F-doped a-BNNRs envisages its applications in Visible-IR optical sensors.

Temperature characteristic of carrier scattering and dark resistivity of semi-insulating GaAs

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.

Electron and hole mobilities of GaN with bulk, quantum well, and HEMT structures

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.