Bulletin of the American Physical Society
84th Annual Meeting of the APS Southeastern Section
Volume 62, Number 13
Thursday–Saturday, November 16–18, 2017; Milledgeville, Georgia
Session D1: Semiconducting and 2D Materials |
Hide Abstracts |
Chair: Mary Ellen Zvanut, University of Alabama Room: MSU Building University Banquet Room A |
Thursday, November 16, 2017 4:00PM - 4:12PM |
D1.00001: Photo-induced EPR spectroscopy of C-doped GaN Subash Paudel, W. R. Willoughby, M. E. Zvanut The Group-III nitride semiconductor GaN is being investigated as an active material in light-emitting diodes and high electron mobility transistors. High-power applications in electronic devices often require semi-insulating substrates, which can be adequately obtained by incorporation of impurities like carbon. We used electron paramagnetic resonance (EPR) spectroscopy to investigate point defects in C-doped GaN. Photo-induced EPR was performed at 3.5 K on 1x10$^{\mathrm{-19}}$ cm$^{\mathrm{-3}}$ C-doped free-standing GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic signal having g $_{\mathrm{\sim }}$1.985 was observed. The intensity of the EPR signal began to decrease at 0.95 $+$/- 0.05 eV and increase at 2.75 $+$/- 0.15 eV during illumination with a quartz tungsten halogen (QTH) lamp using constant photon flux. The 2.75 eV threshold is interpreted as the energy required to excite electrons from the defect to the conduction band minimum, whereas the 0.95 eV threshold is interpreted as the energy required to excite electrons from the valance band maximum to the defect indicating a deep level defect. This deep level is assumed to be the cause of the electrical compensation and high resistivity in C-doped GaN. [Preview Abstract] |
Thursday, November 16, 2017 4:12PM - 4:24PM |
D1.00002: EPR studies and consequences of oxygen annealing on the electrical properties of Mg-doped In$_{\mathrm{2}}$O$_{\mathrm{3}}$ thin films Suman Bhandari, M. E. Zvanut Indium oxide (In$_{\mathrm{2}}$O$_{\mathrm{3}})$ is a transparent conducting oxide that can be thought of as a potential candidate for applications in transparent electronics. Defects in In$_{\mathrm{2}}$O$_{\mathrm{3}}$ thin films are studied using electron paramagnetic resonance (EPR) and their contributions to electrical properties are investigated by Hall measurements. An In$_{\mathrm{2}}$O$_{\mathrm{3}}$:Mg thin film, deposited on r-Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ by plasma assisted molecular beam epitaxy, was annealed for 30 min in O$_{\mathrm{2}}$ from 200 \textdegree C to 900 \textdegree C and analyzed by EPR at 300 K. The EPR results show a monotonic decrease in defect concentration with increase in annealing temperature. The isotropic g-value of the defect is 2.0054. An increase in resistivity and decrease in electron concentration were reported by others after O$_{\mathrm{2}}$ annealing of similar samples. The results are consistent with our EPR data and suggest that the defect detected by EPR is an oxygen vacancy. To further understand the material, the effect of O$_{\mathrm{2}}$ annealing on In$_{\mathrm{2}}$O$_{\mathrm{3}}$, doped with different Mg concentrations, will be presented at the conference. The preliminary results show an increase in resistivity and decrease in defect concentration as Mg increases. The data suggest a model that the donors, assumed to be the EPR detected defects, are compensated by the Mg acceptor. [Preview Abstract] |
Thursday, November 16, 2017 4:24PM - 4:36PM |
D1.00003: Ion Migration Studies in 2D Molybdenum Trioxide Thin Flake through Ionic Liquid Gating Cheng Zhang, Pushpa Pudasaini, Akinola Oyedele, Anthony Wong, Anna Hoffman, Kai Xiao, David Mandrus, Thomas Ward, Philip Rack Ionic liquid is well known for its ability to electrostatically enhance the carrier densities of devices and thin films. The formation of an electric double layer can electrostatically induced charge carriers and/or intercalate ions in and out of the lattice which can induce a large change of the electronic and optical properties and even crystal structures. We present a systematic study on exfoliated molybdenum trioxide devices regarding the property changes and the underlying ion migration during the biasing process through ionic liquid. A close to nine orders of magnitude modulation of the MoO$_{\mathrm{3}}$ conductivity was obtained via ionic liquid gating. Two types of ionic liquids are involved and rapid on/off switching can be realized through the lithium containing ionic liquid. Secondary ion mass spectrometry investigation is performed which reveals the ion migration details. [Preview Abstract] |
Thursday, November 16, 2017 4:36PM - 4:48PM |
D1.00004: Graphene superlattices in strong circularly polarized fields: Detecting Berry phase without magnetic field Hamed Koochaki Kelardeh, Vadym Apalkov, Mark Stockman We theoretically explore the electron dynamics of graphene superlattices created by strong circularly-polarized ultrashort pulses. The conduction-band population distribution in the reciprocal space forms an interferogram with discontinuities related to the topological (Berry) fluxes at the Dirac points. One of the fundamental problems of topological physics of graphene is a direct observation of the Berry phase. This is related to the fact that the only realistic possibility of observing this phase is self-referenced interferometry of electronic waves in the reciprocal space. However, the Berry phase is $\pm\pi$; the self-referenced interferometry doubles it to $\pm 2\pi$, which does not produce any discontinuities in the interference fringes. The Bragg scattering from the superlattices creates diffraction and “which way” interference in the reciprocal space reducing the Berry phase and making it directly observable in the electron interferograms. Our finding is an essential step in control and observation of ultrafast electron dynamics in topological solids and may open up a route to all-optical switching, ultrafast memories, and room temperature superconductivity technologies. [Preview Abstract] |
Thursday, November 16, 2017 4:48PM - 5:00PM |
D1.00005: Ultrafast Electron And Lattice Dynamics Omadillo Abdurazakov, Avinash Rustagi, James Freericks, Alexander Kemper The electron-lattice interactions have been subject to intense study since the dawn of condensed matter physics. Recent advances in the pump-probe spectroscopy brought about a fresh perspective into their fundamental role in the normal and emergent phases of matter. We study the ultrafast dynamics of the excited electron populations in a 2D band by a laser pump field when coupled to the optical phonons with the fixed and dynamically updated properties. The trARPES spectra of photoexcited electrons indicate that the inclusion of phonon dynamics strongly influences the single particle as well as many-body properties. The spectra acquire a diffused and broad structure owing to the increased phonon occupation. We also observe that the kink, traditionally regarded as the strength of the electron-phonon interaction, is strongly weakened. The population decay rates are found to be time-dependent; they are enhanced below the phonon frequency due to phase space considerations. The pump field also induces temporal modifications in the phononic properties. These are seen in the transient stiffening of the phonon frequency and the decay rates. Our results have implications in controlling and characterizing the charge carrier and structural dynamics with ultrashort pump pulses. [Preview Abstract] |
Thursday, November 16, 2017 5:00PM - 5:12PM |
D1.00006: Photoemission signature of excitons Avinash Rustagi, Alexander Kemper Angle resolved photoemission spectrocopy (ARPES) is used to investigate the properties of a system both in and out of equilibrium. While the tools of many body theory has successfully explained the electronic spectra modifications due to interactions, the signatures of electron-hole bound states i.e. excitons in ARPES measurements requires further study. We theoretically study the signature of excitons on the equilibrium ARPES spectra by evaluating the photoemission intensity of electron from the electron-hole bound state. We apply our results to a simple two-band model for transition metal dichalcogenides (TMDCs) with exciton states described by hydrogenic orbitals and study the effects of exciton Bohr radii and the bound state wavefunction on the photoemission intensity. [Preview Abstract] |
Thursday, November 16, 2017 5:12PM - 5:24PM |
D1.00007: Equation of State and Densification of Borosilicate Glass under High Pressure Kathryn Ham, Yogesh Vohra, Yoshio Kono, Parimal Patel A reprocessed sample of borosilicate glass has been studied by X-ray radiography and multi-angle energy-dispersive X-ray diffraction to 12.2 GPa using a Paris-Edinburgh (PE) press at Beamline 16BM-B, HPCAT of the Advanced Photon Source. Gold foil pressure markers were used to obtain the sample pressure by X-ray diffraction, while X-ray radiography provided a direct measure of sample volume. The X-ray radiography method for volume measurements at high pressures was validated for a known sample of pure $\alpha $-Iron. The experimentally measured equation of state of reprocessed borosilicate glass was fitted to a third-order Birch- Murnaghan equation. The bulk modulus of 28.81 GPa obtained from the measured equation of state is in good agreement with the 30.4 GPa value derived from the measured elastic constants. The flotation density of sample decompressed from 12.2 GPa is 2.755 gm/cc and shows an increase in density of 24{\%} as compared to the starting sample. [Preview Abstract] |
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