Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B28: Semiconductors: Thermal Transport and Characterization |
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Sponsoring Units: FIAP Chair: Matt Kim, QuantTera Room: 291 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B28.00001: Exploiting non-local analysis of lattice thermal conductivity Philip B. Allen Small Q phonons have very slow relaxation rates $1/\tau_Q$. This causes the heat current $j(x)$ to depend on the temperature gradient $dT(x^\prime)/dx^\prime$ at long distances $|x-x^\prime|$. In a homogeneous crystal, the Fourier-space representation $j(q)=-\kappa(q) dT/dx(q)$ is helpful; I use this to analyze simulations\footnote{X. W. Zhou {\it et al.}, Phys. Rev. B \textbf{79}, 115201 (2009).}\footnote{Z. Liang {\it et al.}, J. Appl. Phys. \textbf{118}, 125104 (2015).} of GaN thermal conductivity. The Peierls-Boltzmann equation in relaxation time approximation gives a formula for $\kappa(q)$. Using a Debye model, explicit results $\kappa_p(q)$ are found for models where $1/\tau_Q\propto Q^p$. Numerics often gives exponents $p$ to be 2, 3, or 4. When $p=2$, $\kappa_2(q)\sim\kappa_0-C\sqrt{q}$. This shows that simulations on samples of size $L$ should be extrapolated by plotting $\kappa(L)$ {\it versus} $1/\sqrt{L}$. For exponent $p\ge 3$, $\kappa(q)$ diverges as $q\rightarrow 0$, which means that $\kappa(L)$ diverges as $L\rightarrow\infty$. An improved analysis is described, which uses Callaway's version of the relaxation time approximation, treating $N$ and $U$ processes separately. [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B28.00002: A first-principles Green-Kubo method for thermal conductivity Jun Kang, Lin-Wang Wang Green-Kubo (G-K) method is widely used to calculate the thermal conductivity of materials. In this method, the thermal conductivity is related to the time correlation function of heat current. Up to date, the application of the G-K formalism is mostly limited in molecular dynamic (MD) calculations based on classic force-field. The combination of the G-K method with more accurate density functional theory (DFT) calculations is prevented by two issues: (i) the energy on each atom is needed to calculate the heat current and (ii) the heat current in the original G-K formalism is ill-defined for a periodic system. In this work, we address the two issues and develop a first-principles G-K method. We obtain an energy density based on the total energy formalism in DFT, and decompose it into each atom by using the charge density of the corresponding isolated atom as a weight function. For the calculation of heat current, we divide each MD step into two sub-steps, and create boundaries with zero heat current in each sub-step. The heat current within the boundaries is well defined and can be properly calculated. Finally we apply the proposed method to liquid argon. The results agree well with those obtained from classic MD calculations, indicating the validity of our method. [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B28.00003: Scattering phase space and Brillouin zone integrations toward understanding phonon thermal transport properties Lucas Lindsay Phonon-phonon interactions arising from lattice anharmonicity most often provide the dominant resistance for thermal energy transfer in semiconductors and insulators. These interactions are governed by fundamental energy and crystal momentum conservation conditions, which define the amount of scattering available to phonons, and thus dictate mode lifetimes and thermal conductivity (k). This work will discuss how various aspects of phonon dispersions determine phase space and k, specifically applied to light atom materials: LiH and LiF. Also, various Brillouin zone integration schemes used to define this phase space and other phonon properties will be discussed, for example, as they are applied to calculate k accumulation with mean free path for Si and MgO. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B28.00004: Phonon thermal transport in 2H, 4H and 6H silicon carbide from first principles Nakib Protik, Ankita Katre, Lucas Lindsay, Jesus Carrete, B. Dongre, G.K.H. Madsen, Natalio Mingo, David Broido Silicon carbide (SiC) is widely used in electronic devices, in part because its high thermal conductivity helps prevent `hot spots' to maintain uniform device operating temperatures. Here we present \textit{ab initio} calculations of the in-plane and cross-plane thermal conductivities, k$_{\mathrm{in}}$ and k$_{\mathrm{out}}$, of the hexagonal SiC polytypes, 2H, 4H and 6H. These calculations combine a full solution of the phonon Boltzmann equation with accurate determination of interatomic force constants from density functional theory. Generally, k$_{\mathrm{out}}$ values are found to be smaller than k$_{\mathrm{in}}$ values for a given polytype. Both k$_{\mathrm{in}}$ and k$_{\mathrm{out}}$ decrease with increasing n in nH SiC. This finding is contrary to previous measurements, which showed 4H SiC having lower k than 6H SiC [1]. Specific comparisons will be made to existing measured and calculated results. We will also discuss the formation of defects, and their effect on thermal conductivity. [1] D. T. Morelli, J. P. Heremans, C. P. Beetz, W. S. Yoo, and H. Matsunami, Appl. Phys. Lett. 63, 3143 (1993); Rusheng Wei, et al., J. Appl. Phys. 113, 053503 (2013). [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B28.00005: Thermoelectric transport in two-dimensional giant Rashba systems Cong Xiao, Dingping Li, Zhongshui Ma, Qian Niu Thermoelectric transport in strongly spin-orbit coupled two-dimensional Rashba systems is studied using the analytical solution of the linearized Boltzmann equation. To highlight the effects of inter-band scattering, we assume point-like potential impurities, and obtain the band-and energy-dependent transport relaxation times. Unconventional transport behaviors arise when the Fermi level lies near or below the band crossing point (BCP), such as the non-Drude electrical conducivity below the BCP, the failure of the standard Mott relation linking the Peltier coefficient to the electrical conductivity near the BCP, the enhancement of diffusion thermopower and figure of merit below the BCP, the zero-field Hall coefficient which is not inversely proportional to and not a monotonic function of the carrier density, the enhanced Nernst coefficient below the BCP, and the enhanced current-induced spin-polarization efficiency. [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B28.00006: Phonon-defect scattering and thermal transport in semiconductors: developing guiding principles Carlos Polanco, Lucas Lindsay First principles calculations of thermal conductivity have shown remarkable agreement with measurements for high-quality crystals. Nevertheless, most materials contain defects that provide significant extrinsic resistance and lower the conductivity from that of a perfect sample. This effect is usually accounted for with simplified analytical models that neglect the atomistic details of the defect and the exact dynamical properties of the system, which limits prediction capabilities. Recently, a method based on Greenâ€™s functions was developed to calculate the phonon-defect scattering rates from first principles. This method has shown the important role of point defects in determining thermal transport in diamond and boron arsenide, two competitors for the highest bulk thermal conductivity. Here, we study the role of point defects on other relatively high thermal conductivity semiconductors, e.g., BN, BeSe, SiC, GaN and Si. We compare their first principles defect-phonon scattering rates and effects on transport properties with those from simplified models and explore common principles that determine these. Efforts will focus on basic vibrational properties that vary from system to system, such as density of states, interatomic force constants and defect deformation. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B28.00007: Anomalous thermal Hall effect in a disordered Weyl ferromagnet Atsuo Shitade Thermal Hall effect is a heat analog of the Hall effect, namely, the heat current flows perpendicular to a temperature gradient. According to the Wiedemann-Franz law, the Lorenz ratio $L^{ij}\equiv \kappa^{ij}/T\sigma ^{ij}$ goes to the universal Lorenz number $L_{0} \equiv \pi^{2}k_{B}^{2} /3e^{2}$ as $T\to 0$, in which $\sigma^{ij}$ and $\kappa^{ij}$ are the electric and thermal (Hall) conductivities and $T$ is temperature. At finite temperature, we can investigate effects of inelastic scattering by the breakdown of the Wiedemann-Franz law. In spite of its usefulness, it is theoretically difficult to calculate $T\kappa^{xy}$ because it is not expressed by the Kubo formula $T\tilde{{\kappa }}^{xy}$ alone but is corrected by the heat magnetization $2M_{Qz} $. Recently, I found a gravitational vector potential coupled to the energy current and established the Keldysh formalism to calculate $T\tilde{{\kappa }}^{xy}$ and $2M_{Qz} $ even in disordered or interacting systems [1]. Here I apply this formalism to a disordered Weyl ferromagnet which exhibits the anomalous (thermal) Hall effect. I first quantum-mechanically calculate $\sigma^{ij}$ and $T\kappa^{ij}$ on an equal footing and reproduce the Wiedemann-Franz law. This is the first step towards a unified theory of the anomalous Hall effect at finite temperature, in which inelastic scattering by magnons is relevant. [1] A. Shitade, Prog. Theor. Exp. Phys. 2014, 123I01 (2014). [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B28.00008: Measuring the Thermal Hall Effect with Oxygen-18 Annealed Strontium Titanate Capacitive Thermometry Colin Tinsman, Ziji Xiang, Gang Li, Fan Yu, Tomoya Asaba, Benjamin Lawson, Lu Chen, Lu Li The thermal Hall effect shows promise as a method for characterizing materials with novel physics. However, measurements of the thermal Hall effect are challenging to make since widely used methods of thermometry display magnetic field dependence at low temperature. In order to make accurate measurements of temperature in high magnetic fields, we have developed thermometers using strontium titanate (STO), which has an increasing dielectric constant at low temperature to a tendency towards ferroelectricity. Although ferroelectric order is destroyed in STO at low temperature by quantum fluctuations, the introduction of oxygen-18 into the material by high temperature annealing has been shown to induce a ferroelectric transition at finite temperature. This allows us to tune the low-temperature behavior of the dielectric constant to create a thermometer with little magnetic field dependence below 1.5 K. We also show our preliminary work on making thermal Hall measurements using these thermometers. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B28.00009: Photo-excited charge carrier suppress sub-terahertz phonon mode in silicon at room temperature Bolin Liao, Alexei Maznev, Keith Nelson, Gang Chen There is a growing interest in the mode-by-mode understanding of electron and phonon transport for improving energy conversion technologies, such as thermoelectrics and photovoltaics. Whereas remarkable progress has been made in probing phonon-phonon interactions, it has been a challenge to directly measure electron-phonon interactions at the single-mode level, especially their effect on phonon transport above cryogenic temperatures. Here we use three-pulse photoacoustic spectroscopy to investigate the damping of a single sub-terahertz coherent phonon mode by free charge carriers in silicon at room temperature. Building upon conventional pump-probe photoacoustic spectroscopy, we introduce an additional laser pulse to optically generate charge carriers, and carefully design temporal sequence of the three pulses to unambiguously quantify the scattering rate of a single phonon mode due to the electron-phonon interaction. Our results confirm predictions from first-principles simulations and indicate the importance of the often-neglected effect of electron-phonon interaction on phonon transport in doped semiconductors. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B28.00010: Spectroscopy of hot carriers in InAs based multi quantum wells for solar cells applications B. A. Magill, M. A. Meeker, R. H. Mudiyanselage, A. Messager, V. R. Whiteside, I. R. Sellers, S. Vijeyaragunathan, M. B. Santos, G. A. Khodaparast In hot carrier solar cells (HCSC), phonons created by incident photons with energies greater than the band gap of the material are reabsorbed by the photo-excite carriers, resulting in an increase in the conversion efficiency of the device. If the phonons are to be reabsorbed the absorber material needs to have phonon lifetime longer than the carrier lifetimes and the contacts need to be energy sensitive, allowing the carriers to be extracted only over a narrow energy range, thus minimizing energy transfer through carrier cooling. In this talk we present PL measurements of $InAs/AlAs_{0.84}Sb_{0.16}$ multi quantum wells (designed to decouple phonon-mediated reaction of the hot carriers through spatial separation of the created charge carriers), as a function of wavelength, intensity, and temperature over a range of 1.4 to 2.1 microns. We compare our results to computational models of the band structure in these materials to answer which layers in the multi quantum well devices the charge carriers reside in, to both refine our current theoretical models for this system and give insight in designing new generations of HCSC based on type II semiconductor transitions. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B28.00011: Evidence for phase transition in the incoherent lattice fluctuations, lattice distortion and local microstructure of pure and implanted SrTiO$_{\mathrm{3}}$ Kalyan Sasmal, Wei-Kan Chu Low temp Rutherford Backscattering Spectrometry-Axial Ion Channeling used to probe displacive structural phase transition (PT) {\&} Jahn-Teller (JT) lattice distortion in perovskite SrTiO$_{\mathrm{3}}$. It provides direct evidence of incoherent lattice fluctuations as function of temp across non-ferroelectric (FE) 2$^{\mathrm{nd}}$ order antiferrodistortive cubic to body-centered tetragonal structural PT at Curie-Weiss T$_{\mathrm{0}}=$105 K, caused by antiphase tilting of TiO$_{\mathrm{6}}$ octahedra by minimizing Gibbs free energy,~opens bandgap {\&} weakens FE instability by reducing cross gap hybridization. Defects in semiconducting SrTiO$_{\mathrm{3\thinspace }}$narrows large band gap {\&} raises Fermi level into conduction band {\&} ensures conductivity. JT effect occur for degenerate filled {\&} empty molecular orbitals. Critical channeling angle $\psi_{\mathrm{c\thinspace }}${\&} ratio of minima of angular RBS-ICh spectral yield $\chi_{\mathrm{min}}$ for Sr {\&} Ti sublattices determine JT lattice distortion in transition element (Fe, Cr etc.) implanted SrTiO$_{\mathrm{3}}$. Similar $\psi_{\mathrm{1/2}}$ values for Sr sublattice indicates no displacement of Sr. Distortion of Ti sublattice infers implanted Fe {\&} Cr is actually located in Ti positions but not in interstitial positions. Temp dependence of Thermal vibrational amplitudes of Sr {\&} Ti also displacements of Ti$^{\mathrm{4+}}$ are calculated based on Linhard's continuum model. Implanted SrTiO$_{\mathrm{3}}$ shows a minor tetragonal phase corresponds to lattice expansion along c-axis {\&} it's not randomly oriented. Local microstructure {\&} atomic distortions studied with HR-TEM (FIB prepared), XPS, GID-XRD {\&} Raman Scattering. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B28.00012: Study of Thermal Properties of FeRh Across First-order Magnetic Phase Transition Gaohua Zhu, Qiye Zheng, Khoa Vo, Debasish Banerjee, Daniel Shoemaker, David Cahill The B2-ordered intermetallic compound FeRh exhibits a first-order phase transition from antiferromagnetic (AFM) order to ferromagnetic (FM) order near room temperature, which makes it an attractive material for both fundamental and applied study. Remarkably, the AFM to FM metamagentic transition is also accompanied by large increase in the electrical conductivity and an abrupt expansion in the lattice structure. The corresponding thermal conductivity change caused by the magnetic transition has never been reported. In this study we investigate AFM to FM transition induced thermal transport property change. The FeRh samples were prepared by arc melting and the thermal conductivity was measured by time-domain thermoreflectance (TDTR). We will discuss interplay of lattice and electronic components of thermal conductivity across the magnetic transition. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B28.00013: An Inelastic X-ray Study of the Ferroelectric Phase Transition in SnTe Christopher O'Neill, Dmitry Sokolov, Andreas Hermann, Alexei Bossak, Christopher Stock, Andrew Huxley SnTe was originally studied in the context of lattice vibrations in diatomic lattices [1]. There has been a recent renewal of interest due to its identification as a crystalline topological insulator, which is related to its room temperature {\em fcc} rocksalt structure [2]. However, the material undergoes a phase transition to a rhombohedral structure upon cooling, strongly affecting its topological states. While the transition is predicted to be a displacive ferroelectric transition, no ferroelectric response has previously been seen due to free carrier screening. We report inelastic x-ray measurements showing the low energy transverse-optic phonon soften to near zero energy at the structural transition [3]. Importantly, the energy of this mode increases again at temperatures below the transition temperature, proving SnTe undergoes a ferroelectric displacement. Density functional calculations that account for the ferroelectric transition and phonon linewidth changes consistent with anharmonic coupling will also be discussed. [1] G. S. Pawley, W. Cochran, R. A. Cowley, and G. Dolling, Phys. Rev. Lett. 17, 753 (1966). [2] T. Hsieh, H. Lin, et al. Nat Comm 3, 982 (2012). [3] C.D. O'Neill, D. Sokolov, A. Hermann, A. Bossak, C. Stock and A.D. Huxley. (submitted) [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B28.00014: First principles investigation of the structural, dynamical, dielectric properties of kesterite, stannite and PMCA phases of Cu$_2$ZnSnS$_4$ Sriram Poyyapakkam Ramkumar, Yannick Gillet, Anna Miglio, Michiel J. van Setten, Xavier Gonze, Gian-Marco Rignanese Cu$_2$ZnSnS$_4$ (CZTS) is a promising material as an absorber in photovoltaic applications. The measured efficiency, however, is far from the theoretically predicted value for the known CZTS phases. To improve the understanding of this discrepancy we investigate the structural, dynamical, and dielectric of the three main phases of CZTS (kesterite, stannite, and PMCA) using density functional perturbation theory (DFPT). The effect of the exchange-correlation functional on the computed properties is analyzed. A qualitative agreement of the theoretical Raman spectrum with measurements is observed. However, none of the phases correspond to the experimental spectrum within the error bar that is usually to be expected for DFPT. This corroborates the need to consider cation disorder and other lattice defects extensively in this material. [Preview Abstract] |
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