Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R33: Semiconductors and Applications I |
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Sponsoring Units: FIAP Chair: Mike Capano Room: BCEC 204B |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R33.00001: Local Magnetic Imaging of Epitaxial Magnetic Insulator on Semiconductor Nanowire Zheng Cui, Sean J Hart, Liu Yu, Saulius Vaitiekenas, Charles M Marcus, Peter Krogstrup, Kathryn Ann Moler The observation of properties related to Majorana bound states in indium arsenide (InAs) nanowire-epitaxial aluminum hybrid structure has been encouraging, but the need for a large external magnetic field makes their control and application very challenging. To locally introduce a magnetic exchange field, a single-crystalline ferromagnetic insulator europium sulfide (EuS) has been grown directly onto the InAs nanowire. Using a scanning Superconducting QUantum Interference Device (SQUID) microscope, we study the local magnetization and susceptibility of the hybrid magnetic structure on a sub-micron scale. Imaging local magnetic properties as a function of temperature and external field on multiple devices allow us to characterize homogeneity, anisotropy and domain formation, which will be crucial to further develop these topological superconducting devices. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R33.00002: Magnetic Field Dependent Transport Measurements on High Quality InAs Nanowires Markus Ritter, Zijin Lei, Benjamin Madon, M A Mueed, Aakash Pushp, Heinz Schmid, Thomas Ihn, Klaus Ensslin, Heike Riel, Fabrizio Nichele Semiconductor nanowires with strong spin-orbit interaction are attracting considerable interest as potential platform for spintronic and topological quantum computing applications. However, future progress will require scalability and integration concepts that go well beyond the single nanowire level. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R33.00003: Strain-induced Gunn Effect in Silicon Nanowires Daryoush Shiri, Amit Verma, Reza Nekovei, Andreas Isacsson, Selva Selvakumar, Anant Anantram Gunn (or Gunn-Hilsum) Effect and its associated negative differential resistivity (NDR) des not exist in bulk silicon. This effect which is due to transfer of electrons between two different energy subbands, is very pronounced in direct bandgap semiconductors like GaAs which makes them favorable for microwave Gunn-diode based oscillators. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R33.00004: The effect of ultrasmall grain sizes on the thermal conductivity of nanocrystalline silicon thin films Xiao Liu, Battogtokh Jugdersuren, Brian T Kearney, James Clifford Culbertson, Christoph N chervin, Rhonda Michele Stroud We report on the thermal conductivity of nanocrystalline silicon thin films with average grain sizes varying from 3 nm to 10 nm. The films were prepared by plasma-enhanced chemical-vapor deposition. The crystallinity and grain sizes of the films are controlled by hydrogen dilution during growth. Thermal conductivity was measured from 80 K to room temperature. The thermal conductivity of the film with 10 nm grain size roughly follows the minimum thermal conductivity predicted for amorphous silicon. As the grain size decreases to 3 nm, its thermal conductivity is reduced to one third of the minimum thermal conductivity. We extend the model of grain boundary scattering of phonons with Debye and Born–von Karman dispersion relations to explain our results. Although our results can still be explained by strong grain boundary scattering, we find the phonon mean-free-path would have to decrease at a faster rate than the reduction of grain size to explain the strong dependence of thermal conductivity on grain size. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R33.00005: First-principles calculation of the dynamic heat current in semiconductors under the application of a thermal gradient Éamonn Murray, Ivana Savic, Stephen B Fahy We present calculations of the time evolution of the thermal transport through a material following the application of a thermal gradient. This involves the calculation of the anharmonic force constants from first principles, which are used to find the scattering between phonon modes of different energies and wavelengths. We can then use this to find the dynamical heat current from the Boltzmann transport equation, going beyond the single mode relaxation time approximation and allowing us to see how the heat current evolves in time once the thermal gradient is applied or changes. We present results of this analysis as applied to several semiconductor systems. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R33.00006: Ginzburg-Landau-Langevin theory and SSH model for Peierls transition in In/Si(111) Yasemin Ergun Motivated by the thermal and photo-induced first-order Peierls transitions observed in atomic wires on semiconducting surfaces [1], we use the Ginzburg-Landau (GL) theory for charge-density-wave systems to investigate the dynamics of collective excitations in Peierls insulators. This formalism allows us to study the vibrations and the non-equilibrium dynamics of the amplitude modes (lattice distortion and density modulation) which are involved in a Peierls transition. We include no phase mode but amplitude modes for the commensurate Peierls system. The Langevin formalism is used |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R33.00007: First-principles calculations of second order nonlinear optical coefficients in the static limit and Pockels coefficients in III-N and II-IV-N2 compounds Sai Lyu, Walter R L Lambrecht The second order nonlinear optical coefficients in the static limit are evaluated using density functional perturbation theory from the electronic response to a static electric field for the group III nitrides and several II-IV-N2 ternary nitrides. They are compared with literature results using the sum over states approach including local field effects. The effects of the scissor correction are evaluated. Good agreement is obtained for GaN, AlN and w-BN. For InN, the small or even negative gap in in the LDA at Γ causes an extreme sensitivity to the k-point summation and pseudopotentials. Similar problems occur for other very small gap II-IV-N2 semiconductors. The nonlinear optics coefficients are showing a general trend of increasing values with smaller gaps but no clear scaling relation with the direct gaps is obtained. The Pockels coefficient, which include in addition to the electronic response, also the phonon and piezoelectric response and are also evaluated. They show that the phonon and electronic contributions to the response in these materials are comparable in magnitude. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R33.00008: Crystal free energy of SiC polytypes and stacking faults formation energy from DFT-based lattice-dynamics approach. Emilio Scalise, Anna Marzegalli, Francesco Montalenti, Leonida Miglio Despite a rising impact of SiC technology in the power electronics industry, some fundamental aspects of this material lack physical understanding. Particularly polytypism and growth of SiC polytypes have been discussed as a paradox from about thirty years because of an evident discrepancy between theory and experiments, not yet elucidated. SiC has more than 200 polytypes and few of them (i.e. 3C, 6H, 4H) are commercially available and used for power devices. Besides the scientific interest, investigating SiC polytypism and understanding its driving force is crucial to correctly predict the energetics of extended defects in SiC, which are one of the main concerns of this wide band gap semiconductor. We perform first-principle calculations, including long range interactions and based on a lattice dynamics approach, we predict the temperature dependent thermodynamic stability of different SiC polytypes which may explain their growth at different temperature. Finally, we estimate the formation energy of stacking faults in SiC and the effect of Van Der Waals corrections are proved to be key for reproducing experimental observations. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R33.00009: High-mobility InAs two dimensional electron systems on GaSb substrates Anthony Hatke, Candice Thomas, Aymeric Tuaz, Ray Kallaher, Tialung Wu, Tian Wang, Rosa Diaz, Geoffrey C. Gardner, Mike Capano, Michael Manfra The two dimensional electron gas in InAs quantum wells grown on nearly lattice-matched GaSb substrates is an attractive stage for mesoscopic device physics. However, use of this system has remained difficult due to outstanding challenges. Here we report on heterostructure design optimization and device fabrication that satisfies three main criteria for mesoscopic device operation: electrical isolation from the semiconducting substrate, ability to fully deplete the charge carriers and control residual sidewall conduction with lithographic gates, and high mobility to ensure ballistic transport over mesoscopic length scales [1]. In addition, we discuss our current progress in realization of mesoscopic devices including quantum point contacts and quantum dots. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R33.00010: High thermal conductivity in cubic boron arsenide crystals Sheng Li, Qiye Zheng, Yinchuan Lv, Xiaoyuan Liu, Xiqu Wang, Pinshane Huang, David G Cahill, Bing Lv We report our experimental efforts on the high thermal conductivity above 1000 W/m/K in the zinc blende cubic BAs crystals. First principle calculations have predicted the thermal conductivity of BAs, is second only to that of diamond at room temperature, which may constitute a useful thermal management material for high–power density electronic devices. Herein, we reported our experimental efforts to grow single domain, defect-free, and large size BAs crystals, evidenced by both single crystal diffraction and scanning transmission electron microscopy (STEM) studies, through test and optimization various single-crystal growth methods. Furthermore, the time-domain thermoreflectance (TDTR) measurement of the BAs crystal gives a high thermal conductivity ~1000 W/m K which is consistent with the predicated value based on four phonon calculations, representing BAs as a new class of ultrahigh thermal conductivity materials. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R33.00011: Interplay between molecular packing and charge transfer states in 6,13-bis(trisopropylsilylethynyl)-pentacene (TIPS-pentacene) organic semiconductor thin films Yang Li, Jing Wan, Detlef-M Smilgies, John M. Hughes, Randall Headrick The optical properties of organic semiconductors are influenced by interference between neutral molecular excitations and charge transfer excitations. We present a comprehensive study of this effect for TIPS-pentacene in the temperature range from 25°C to 140°C via the influence of molecular packing on the optical and electronic properties, utilizing in-situ x-ray diffraction, polarized optical spectroscopy and density functional theory. In TIPS-pentacene, anisotropic thermal expansion causes neighboring molecules to “slide” relative to each other. Since charge transfer effects depend sensitively on the nodal structure of the highest occupied and lowest unoccupied molecular orbitals, optical excitations are modulated as the relative displacement is varied. We find that the transition energies of the lowest energy optical excitations are dramatically blue shifted as the temperature is increased, and that changes in the charge transfer integrals can be correlated with an enhancement of field-effect transistor mobility. These results suggest a new approach to improve carrier mobility in strained thin films by decreasing the sensitivity of the charge transfer integrals to dynamic disorder. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R33.00012: Overcoming bismuth saturation in GaAsBi by manipulating film strain Margaret Stevens, Kevin Grossklaus, John McElearney, Thomas Vandervelde Epitaxially grown III-V-Bismides offer new band gap and lattice constant combinations for near- and mid-IR device applications on GaAs and InP substrates. High bismuth content GaAsBi is typically grown compressively strained on GaAs, though droplet-free thick films have been difficult to realize in that system. Surface Ga-Bi droplets inhibit bismuth incorporation and cause vertical phase separation, yielding films unusable for optoelectronic applications. To produce bismide films that are suitable for IR optoelectronics, we explored the growth of increasingly Bi-rich GaAsBi compounds under a variety of strain conditions ranging from highly compressively strained on GaAs to tensile strained on InGaAs buffer layers. High resolution x-ray diffraction and Rutherford backscatter spectrometry showed higher Bi content can be achieved without droplet formation by reducing film compressive strain. Atomic force microscopy and phase contrast microscopy showed reduced surface droplet density, indicating bismuth is being incorporated in the film rather than surface segregating. Overall, we show that reducing the compressive strain in GaAsBi films is a successful method for reducing droplet formation and enabling increased Bi incorporation. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R33.00013: Geometry Dependence of Quantum Point Contact Conductance Albert Chang, Phillip M. Wu, Hao Zhang We present evidence that quantum point contacts (QPCs) fabricated on a high mobility (~106 cm2/Vs) GaAs/AlGaAs heterstructure crystal with doping close to the 2D interface exhibit quantum transport conductance which is strongly dependent on the QPC geometry. In particularly, asymmetrically shaped, T-junction QPCs nearly always exhibit strong conductance resonances as well as anomalies in the conductance plateaus, whereas symmetrically shaped QPCs, designed with smooth entrance and exit regions joining to wide 2D regions, are largely devoid of such resonances. The dramatic difference in the conductance traces between the two types of geometries suggest that disorder does NOT play a dominant role in the transport characteristics. Furthermore, this implies that unusal features, including resonances, suppression of quantum plateaus[1,2], and novel differential conductance oscillations [3] previously reported in asymmetric QPCs could arise instead from intrinsic mechanisms, e.g. geometry and/or interaction effects. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R33.00014: The Cold Source Field-Effect Transistor - Exploiting Ballistic Transport to Design a Low Subthreshold Swing Switching Device Raphael Prentki, Fei Liu, Jian Wang, Hong Guo Power dissipations are to blame for part of the recent deceleration in the exponential growth rate of the transistor count on integrated circuits predicted by Moore's law. A relevant metric at the device level is the subthreshold swing (S) - the increment in gate voltage required for a tenfold increase in drain current - which is commensurate with energy losses during switching. For the ubiquitous Si Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), thermodynamics and electrostatics impose that S ≥ 60 mV/dec at room temperature. Phenomena beyond MOSFET physics thus need to be exploited to design a low S device; we show how ballistic transport can be used towards this end. In the resulting device, known as the cold source FET, thermionic emission is suppressed in the OFF-state by means of density-of-states engineering, thereby enabling low S while maintaining a high ON-state current. Deviations from the approximation of ballistic transport need to be considered for real-world implementations; we show how rethermalization due to inelastic scattering affects S. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R33.00015: Self-Modulation Doping Effect in the High-Mobility Layered Semiconductor Bi2O2Se Huixia Fu Recently an air-stable layered semiconductor Bi2O2Se was discovered to exhibit an ultrahigh mobility in transistors fabricated with its thin layers. In this work, we explored the mechanism that induces the high mobility and distinguishes Bi2O2Se from other semiconductors. We found that the electron donor states lie above the lowest conduction band. Thus, electrons get spontaneously ionized from donor sites (e.g., Se vacancies) without involving the thermal activation, different from the donor ionization in conventional semiconductors. Consequently, the resistance decreases as reducing the temperature as observed in our measurement, which is similar to a metal but contrasts to a usual semiconductor. Furthermore, the electron conduction channels locate spatially away from ionized donor defects (Se vacancies) in different van der Waals layers. Such a spatial separation can strongly suppress the scattering caused by donor sites and subsequently increase the electron mobility, especially at the low temperature. We call this high-mobility mechanism self-modulation doping, i.e. the modulation doping spontaneously happening in a single-phase material without requiring a heterojunction. Our work paves a way to design novel high-mobility semiconductors with layered materials. |
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