Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R07: Computational Approaches to Phonons in Semiconductors |
Hide Abstracts |
Sponsoring Units: FIAP Chair: Dipanshu Bansal, Duke University Room: LACC 153B |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R07.00001: First-Principles Prediction of Temperature-Dependent Phonon Energy Shifts Tianli Feng, Juan Idrobo, Sokrates Pantelides Phonon energies of solids at finite temperatures shift from their harmonic values at 0 K due to anharmonicity. Accurate prediction of the frequency shifts is necessary for the study of many areas such as thermal transport, thermodynamical properties, superconductivity, infrared spectroscopy, etc. Here, we report first-principles simulations that predict the temperature-dependent thermal expansion coefficients and phonon energy shifts of monolayer and bulk boron nitride. The calculation results agree with available experimental results. We have also decomposed the frequency shifts into distinct contributions, accounting for the experimental results. The predicted phonon energy shifts are also in agreement with recent experimental measurements in bulk boron nitride using electron energy gain and loss spectroscopies [1]. The first-principles calculations, combined with experiments, show a capability of measuring temperature with nanoscale resolution. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R07.00002: First-principles Monte Carlo simulation of electron transport in AlxGa1-xN/GaN high-electron-mobility transistors Jingtian Fang, Ronald Schrimpf, Massimo Fischetti, Sokrates Pantelides We simulate semiclassical electron transport in wide-band-gap AlGaN/GaN high-electron-mobility transistors (HEMTs), which are widely studied for their application in power electronics. We perform first-principles calculations to obtain the electronic band structures, the phonon dispersions, and the electron-phonon scattering rates of both GaN and AlN in their wurtzite phase. These properties of the ternary alloy AlxGa1-xN are obtained using the virtual crystal approximation starting from GaN and AlN. Applying electrical bias to the AlxGa1-xN/GaN HEMTs, we solve the Boltzmann transport equation (BTE) with the Monte Carlo technique. Five conduction bands are employed for electrons’ kinetics, so that electrons with an energy as high as 8 eV can be described. The Poisson’s equation is solved self-consistently with the BTE while performing the device simulation. We obtain the ensemble Monte Carlo particles’ energy distribution. The results are used to study hot-carrier-induced defect activation and to understand the device degradation. The high-field electron transport capability offered by the full-band Monte Carlo technique is demonstrated throughout the present work. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R07.00003: A comparison of DFT-calculated and experimental mean-squared displacements, elastic constants,
and phonons in skutterudites Joe Feldman, Noam Bernstein We discuss interatomic forces for four skutterudites that have received attention in the literature, LaFe4Sb12, BaCo4Sb12, FeSb3 and CoSb3. We employ the PAW-VASP density functional implementation and a least square procedure to derive quadratic, cubic and quartic Taylor expansion coefficients from LDA- and GGA-PBE-computed atomic forces generated by displacements of single atoms within both conventional and 2X2X2 conventional cells of the skutterudite structure. We compute--and compare with available experiment and theory--second order elastic constants, phonon frequencies, and the mean square atomic displacement tensor as a function of temperature, We are not aware of any published calculations of the full mean square displacement tensor for any skutterudite. A surprising result is that a filler-filler force constant, namely the interaction between atoms on cube-corners, can have a non-negligible (few percent) effect in the phonon dispersion curves: This occurs for LaFe4Sb12 but not for BaCo4Sb12, as the corresponding Ba-Ba interaction is negligibly small. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R07.00004: Three-mode-interactions in the anharmonic phononic coupling process Mingqiang Gu, James Rondinelli Nonlinear phononic coupling is a modern way to manipulate material structure, accessing non-equilibrium state beyond those in the static phase diagram. Presently, most studies focus on a single displacive excitation of a Raman mode that couples to the coherently laser-excited IR mode. However, in principle all the symmetry-allowed Raman modes could be excited simultaneously. When the excited modes strongly interact with each other, the dynamics of the original targeted Raman mode should be different. We demonstrate quantitatively these differences by extending the phonon equations-of-motion to include the IR-Raman-Raman interaction. The displacive amplitude of the targeted Raman mode saturates as the light intensity continues to increase. The energy transfers to the two Raman modes and beating is observed. With first-principles density functional theory calculations, we investigate the three-mode-coupling in the titanate YTiO3 as an example to predict a new magnetic phase not found in the thermodynamic phase diagram. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R07.00005: The effect of strain on the structure of SnS Betul Pamuk, Craig Fennie Tin sulfides are important for semiconductor technologies with potential applications in optoelectronics and solar energy conversion. Bulk SnS has orthorhombic structure with the Pnma symmetry (space group No. 62), with a phase transition to a structure with the Cmcm symmetry (space group No. 63) at 875 K. It is also known that the rocksalt structure with the Fm-3m symmetry (space group No. 225) has been observed by epitaxial growth on rocksalt thin films. Here we present a first principles study of the high symmetry rocksalt structure and its relation to the lower symmetry structures. Furthermore, we investigate the changes to the structure under different epitaxial strain conditions. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R07.00006: Selective quasiparticle breakdown in superionic CuCrSe2 Jennifer Niedziela, Dipanshu Bansal, Andrew May, Jingxuan Ding, Georg Ehlers, Douglas Abernathy, Ayman Said, Olivier Delaire Mechanisms of ionic mobility and the nature of interactions between mobile and stationary ions in superionic compounds have long been debated. A central issue regards the role of phonons in the superionic state where portions of the lattice exhibit liquid-like behavior. Here, we present results of scattering studies on a superionic conductor which also exhibits low lattice thermal conductivity and potential for application in thermoelectrics. We establish co-existence of acoustic phonons and superionic diffusion, and breakdown of the optical modes in the diffuser sublattice. Further, large anharmonic vibrations of the diffuser sublattice precede the superionic transition, and timescales for diffusion of the mobile species in the superionic state are long compared to the relevant acoustic phonon period. These results demonstrate that anharmonic phonon dynamics is common to the origin of low thermal conductivity and superionicity in this class of materials. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R07.00007: Ab initio molecular dynamics study of the structural and electronic transition in VO2 Dušan Plašienka, Roman Martonak, Marcus Newton The temperature-induced structural and electronic transformation in VO2 between the monoclinic M1 and tetragonal R phases was studied by ab initio molecular dynamics, based on the DFT+U scheme. We compare the structure of both phases, transition temperature and atomic fluctuations both above and below the transition, as well as the phonon density of states and scattering intensity of centroid position, with experimental data. The good quantitative agreement indicates that the chosen scheme provides a fairly good description of the energetics of the system. Analysis of the structural transformation was carried out by following the time evolution of dimerization amplitudes of V-atom chains and the twisting angle of V-dimers. The electronic transition was studied by tracing the changes in projected densities of states and their correlation with the evolution of the structural transformation. Our results reveal a strong interconnection between the structural and electronic transformations. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R07.00008: Determination of the pyroelectric coefficient in spontaneously polarized materials Nicholas Pike, Ole Martin Løvvik The pyroelectric coefficient determines the coupling between the spontaneous polarization of a material and changes in the external temperature. While the derivation of this quantity from the definition of the total polarization is straightforward, both measurements and first-principle calculations often disagree on the magnitude of the pyroelectric coefficient. To improve the agreement between experiment and theory we first review the derivation of the pyroelectric coefficient from the modern theory of polarization and then determine the pyroelectric coefficient from a full first-principles calculation. Discrepancies between our calculated temperature dependence and experimental measurement are discussed and analyzed. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R07.00009: Strongly Anharmonic Nuclear Dynamics in Solids: Accurate Computations and Rapid Estimates for Statistical Mechanics Christian Carbogno, Hagen-Henrik Kowalski, Florian Knoop, Maja-Olivia Lenz, Matthias Scheffler Many material properties are determined by the anharmonicity of the potential-energy surface (PES), i.e., by features of the PES that are not captured by a harmonic second-order Taylor expansion. Typically, such effects are treated perturbatively in first-principles calculations by solely accounting for the third-order term in the expansion [1]. Little is yet known about the role of higher-order terms. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R07.00010: Anomalously Temperature-Dependent Thermal Conductivity of Monolayer GaN with Large Deviations from the Traditional 1/T Law Guangzhao Qin, Ming Hu We report that, despite the commonly established 1/T relation of thermal conductivity in plenty of materials, monolayer GaN exhibits anomalous behavior that the thermal conductivity almost decreases linearly over a wide temperature range above 300 K, deviating largely from the traditional κ ∼ 1/T law. The thermal conductivity at high temperature is much larger than the expected thermal conductivity that follows the general κ ∼ 1/T trend, which would be beneficial for applications of monolayer GaN in nano- and optoelectronics in terms of efficient heat dissipation. We perform detailed analysis on the mechanisms underlying the anomalously temperature-dependent thermal conductivity of monolayer GaN in the framework of Boltzmann transport theory and further get insight from the view of electronic structure. Beyond that, we also propose two required conditions for materials that would exhibit similar anomalous temperature dependence of thermal conductivity: large difference in atom mass (huge phonon band gap) and electronegativity (LO-TO splitting due to strong polarization of bond). |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R07.00011: Phonon-Assisted Tunneling in Large-Size Direct-Bandgap Semiconductor Devices Mazharuddin Mohammed, Anne Verhulst, Devin Verreck, Maarten Van de Put, Wim Magnus, Bart Soree, Anda Mocuta, Guido Groeseneken Trap-assisted tunneling (TAT) is one of the probable reasons for a degraded subthreshold swing in TFETs. Phonon-assisted tunneling (PAT), which is a first step towards an implementation of TAT, has not been studied in large semiconductor devices. Therefore, we present a multi-band PAT current formalism within the framework of the quantum transmitting boundary method. We derived the electron-phonon coupling terms using the envelope function approximation, used to calculate direct band-to band tunneling (BTBT) currents. We applied a low-wavevector approximation for local Fröhlich-based phonon-assisted inter-band tunneling in direct-bandgap semiconductors. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R07.00012: First Principle Study of Non-thermal Phase Transition Mechanism with Uniaxial Stress Applied Phase Transition Material : GeTe Hanjin Park, Young-Kyun Kwon Recently, phase change materials (PCM) have attracted attention as candidate for next generation memory device elements. But it has several problems in power consumption, information storage capacity, energy efficiency, and so on. We use ab initio density functional theory to investigate non thermal phase transition of a prototypical phase change material, GeTe, induced by uniaxial strain. We focus on the rhombohedral structure which can be interpreted as a layered strucuture, in which layers are seperated by long bonds. It is found that GeTe layered structure experiences a phase transition from one crytalline phase to the other crystalline one under external uniaxial tensile stress. We identify that the latter phase is essentially regarded as another layered structure rotated from the former phase through the exchange mechansm between short and long bonds. Our electronic transport calculation also shows that the conductance changes significantly during such phase transition, implying that uniaxial strain may induce non-thermal phase transition in GeTe. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R07.00013: Coupled acousto-optical phonons in 2D and bulk materials Morten Willatzen, Lok Lew Yan Voon, Lars Duggen, Zhong Wang In piezoelectric materials acoustic and optical phonons are generally coupled. We present a detailed discussion of symmetry effects in zincblende materials (GaAs as an example) and 2D inversion-asymmetric structures such as molybdenum disulfide. We predict that acousto-optical phonons cannot exist at the LO phonon frequency where the dielectric constant vanishes. We show that confined optical phonon modes exist for the group-IV materials but not for molybdenum disulfide. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R07.00014: Phonon satellite bands in the spectral function of ZnO from first principles Yang-hao Chan, Gabriel Antonius, Steven Louie We present first-principles studies of the spectral function of ZnO near the Fermi level due to electron-phonon coupling. We first compute the self energy using the Dyson-Migdal theory [1]. The computed zero-point renormalization reduces the band gap by about 150 meV. However, the positions of the satellite peaks in the spectral function from the Dyson-Migdal theory deviate from the experimental spectra, and the theory does not yield peaks associated with multiple-phonon absorption/emission. On the other hand, the cumulant approach [2,3,4] provides a better agreement with experiment in terms of satellite spacing and multiple satellite peaks. We find that the satellite energy spacing agrees with the highest energy LO phonon mode, which confirms that satellite structure is induced by strong polar electron-phonon coupling. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700