Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session L7: Dopants and Defects in Semiconductors: Novel experimental techniquesFocus Industry
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Sponsoring Units: DMP FIAP Chair: James Speck, University of California, Santa Barbara Room: 303 |
Wednesday, March 16, 2016 11:15AM - 11:51AM |
L7.00001: Tailoring of materials properties under extreme conditions Invited Speaker: Thomas Schenkel Materials can be driven far from equilibrium e. g. with intense pules of lasers and ions, in mostly destructive processes. When combined with micro- and nano-structuring, the ability to rapidly excite and then quench local excitations opens up. Now opportunities emerge to form and stabilize novel materials phases and to tailor materials properties for applications. Examples are color centers in diamond and silicon carbide for sensing and qubit applications and proposed ordered dopant structures in cuprate superconductors. Results from studies of materials processing under transient extreme conditions, far from equilibrium will be presented. [Preview Abstract] |
Wednesday, March 16, 2016 11:51AM - 12:03PM |
L7.00002: Polarization spectroscopy of defect-based single photon sources in ZnO Nicholas Jungwirth, Hung-Shen Chang, Mingde Jiang, Gregory Fuchs Isolated point-defects in wide bandgap semiconductors are promising candidates for future applications requiring quantum light sources. Recently, defect-based single photon sources have been observed in ZnO that are very bright (\textgreater 100 kCounts/s) and remain photoactive from 4.5 K to room temperature. Despite several investigations, the structure and electronic states of these emitters remain unknown. In this work, we establish a procedure to distinguish a Z dipole from an XY dipole when studying quantum emitters that are randomly oriented. Our cryogenic and room temperature polarization measurements collectively establish that these unidentified ZnO quantum emitters have a Z dipole. We show that the associated absorption and emission dipoles are parallel within experimental uncertainty for all 32 individuals studied. Additionally, we apply group theory and find that, assuming the defect symmetry belongs to a point-group relevant to the ZnO wurtzite lattice, the ground and excited states are orbital singlets. These results are a significant step in identifying the structure and electronic states of defect-based single photon sources in ZnO. [Preview Abstract] |
Wednesday, March 16, 2016 12:03PM - 12:15PM |
L7.00003: A first principle approach using Maximally Localized Wannier Functions for computing and understanding elasto-optic reponse Xin Liang, Sohrab Ismail-Beigi Strain-induced changes of optical properties are of use in the design and functioning of devices that couple photons and phonons. The elasto-optic (or photo-elastic) effect describes a general materials property where strain induces a change in the dielectric tensor. Despite a number of experimental and computational works, it is fair to say that a basic physical understanding of the effect and its materials dependence is lacking: e.g., we know of no materials design rule for enhancing or suppressing elasto-optic response. Based on our previous work, we find that a real space representation, as opposed to a k-space description, is a promising way to understand this effect. We have finished the development of a method of computing the dielectric and elasto-optic tensors using Maximally Localized Wannier Functions (MLWFs). By analyzing responses to uniaxial strain, we find that both tensors respond in a localized manner to the perturbation: the dominant optical transitions are between local electronic states on nearby bonds. We describe the method, the resulting physical picture and computed results for semiconductors. [Preview Abstract] |
Wednesday, March 16, 2016 12:15PM - 12:27PM |
L7.00004: Modification of a scanning electron microscope (SEM) for insitu, nanometer size contact, electrical measurements of III-nitride transistors Camelia Selcu, Zhichao Yang, Sriram Krishnamoorthy, Siddharth Rajan As the transistors become smaller and smaller, proximity effects become important, therefore there is a need for characterization instruments. We modified a scanning electron microscope (SEM) by adding the capability to make mechanical contacts to devices for electrical measurements with nanometer precision. We will discuss ongoing work involving III-nitride transistors and nanowires. [Preview Abstract] |
Wednesday, March 16, 2016 12:27PM - 12:39PM |
L7.00005: Second-Harmonic Generation scanning microscopy of strain fields around Through-Silicon-Vias Yujin Cho, Farbod Shafiei, Bernardo Mendoza, Tengfei Jiang, Paul Ho, Michael Downer Through-Silicon-Vias (TSVs) improve electrical performance of integrated circuits and reduce power consumption by interconnecting vertically stacked silicon layers. Cu has been commonly used for TSVs because of its good electrical and mechanical properties. However, mismatch in thermal expansion coefficient of Si and Cu induces strain fields on the surfaces, which can degrade the performance of nearby devices and crack the surfaces. In this work, using non-invasive Second Harmonic Generation (SHG) microscopy, we successfully characterized inhomogeneous distribution of the thermally induced strain fields. High strain gradients strengthen SHG intensity, since it breaks centrosymmetry in Si. In p-polarized incoming beam and s-polarized SHG configuration, we were able to see the strain effect directly, while in p-in/ p-out polarization, strain-induced SHG was coupled with background SHG from Si [1]. We will present SHG micrographs compared with Raman measurement and the theory of strain-induced SHG, as well as wavelength and power dependence of SHG. [1] Mendoza et al. 'Surface second harmonic generation induced by 3D strain fields', Phys. Status Solidi B. 1-8 (2015) [Preview Abstract] |
Wednesday, March 16, 2016 12:39PM - 12:51PM |
L7.00006: Probing the effect of dopants (donors) within InAs/InGaAs/InAlAs Asymmetric Heterostructure wafer by magneto-THz spectroscopy Mehdi Pakmehr, Christian Heyn, Wolfgang Hansen Probing the effect of impurities within semiconductor structures have been the topic of interest both from applied and scientific point of views. We studied the effect of dopants (donors) within InAs/InGaAs/InAlAs asymmetric heterostructure wafer by means of THz magneto-transmission (TR) spectroscopy, in conjunction with THz magneto-photoresponse (PR) spectroscopy. The sample wafer has been immersed in pumped liquid Helium at 1.6 K, while being exposed to sweeping magnetic field up to 10 Tesla, with THz laser beam (1.4 THz) being focused on sample by off-axis parabolic mirror. The transmitted beam was detected by silicon composite bolometer. Two broad absorption features other than sharp Cyclotron resonance (CR) absorption dip within magneto-TR signal attributed to 1s$\to $2P transition within donors of doped layer (InAlAs) in heterostructure. We plan to discuss the analysis of magneto-TR signal, in conjunction with Magneto-PR signals from Hall bar samples made from same type of wafer at same frequency to clarify how dopants could possibly alter these signals. [Preview Abstract] |
Wednesday, March 16, 2016 12:51PM - 1:03PM |
L7.00007: Sub-surface single ion detection in diamond: A path for deterministic color center creation John Abraham, Brandon Aguirre, Jose Pacheco, Ryan Camacho, Edward Bielejec Deterministic single color center creation remains a critical milestone for the integrated use of diamond color centers. It depends on three components: focused ion beam implantation to control the location, yield improvement to control the activation, and single ion implantation to control the number of implanted ions. A surface electrode detector has been fabricated on diamond where the electron hole pairs generated during ion implantation are used as the detection signal. Results will be presented demonstrating single ion detection. The detection efficiency of the device will be described as a function of implant energy and device geometry. It is anticipated that the controlled introduction of single dopant atoms in diamond will provide a basis for deterministic single localized color centers. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy Office of Science. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, March 16, 2016 1:03PM - 1:15PM |
L7.00008: ABSTRACT WITHDRAWN |
Wednesday, March 16, 2016 1:15PM - 1:27PM |
L7.00009: Uniaxial stress studies of H centers in In$_{\mathrm{2}}$O$_{\mathrm{3}}$ Philip Weiser, Michael Stavola, W. Beall Fowler, Lynn A. Boatner In$_{\mathrm{2}}$O$_{\mathrm{3}}$ single crystals have been grown for our experiments that are sufficiently large to make possible IR absorption measurements in conjunction with uniaxial stress. The introduction of H produces an IR line at 3306 cm$^{\mathrm{-1}}$ that has been assigned to the OH stretching mode of an interstitial H shallow donor in In$_{\mathrm{2}}$O$_{\mathrm{3}}$ [1]. We have performed IR absorption experiments in which the splitting of the 3306 cm$^{\mathrm{-1}}$ line under stresses applied at low temperatures provides information about the symmetry of the OH center. Stress measurements made at elevated temperatures reveal a stress-induced dichroism that provides information about the motion of hydrogen associated with the 3306 cm$^{\mathrm{-1}}$ center. [1] W. Yin \textit{et al}., Phys. Rev. B \textbf{91}, 075208 (2015). [Preview Abstract] |
Wednesday, March 16, 2016 1:27PM - 1:39PM |
L7.00010: Diffusion of H in In2O3 single crystals Ying Qin, Weikai Yin, Mike Stavola, Beall Fowler, Lynn Boatner An IR absorption line observed at 3306 cm$^{-1}$ for In$_{2}$O$_{3}$ single crystals annealed in an H$_{2}$ ambient has been assigned to an interstitial hydrogen center that acts as a shallow donor [1]. Experiments have been performed to determine the indiffusion depth of interstitial H into In$_{2}$O$_{3}$ at temperatures near 400 \textdegree C. We have also performed annealing experiments in which the outdiffusion of interstitial H is monitored by IR spectroscopy. The goal of these studies is to determine the diffusion constant of interstitial H in In$_{2}$O$_{3}$ over a range of temperatures so that the activation energy for diffusion can be determined. [1] W. Yin et al., Phys. Rev. B 91, 075208 (2015). [Preview Abstract] |
Wednesday, March 16, 2016 1:39PM - 1:51PM |
L7.00011: \textbf{Profiling the local carrier concentration and dopant distribution across a semiconductor quantum dot} J.C. Walrath, A.S. Chang, Y.H. Lin, S. Huang, R.S. Goldman We profile the local carrier concentration, n, across epitaxial InAs/GaAs quantum dots (QDs) consisting of 3D islands on top of a 2D alloy layer. We use scanning thermoelectric microscopy to profile the temperature gradient-induced voltage, which is converted to a profile of the local Seebeck coefficient, S. The S profile is then converted to a conduction band-edge profile and compared with Poisson-Schrodinger band-edge simulations. Our combined computational-experimental approach suggests a reduced carrier concentration in the QD center in comparison to that of the 2D alloy layer. We further use 3D atom probe tomography, which enables 3D imaging with a few Angstrom resolution, to profile the distribution of Si dopants. We discuss the correlation between the Si dopant distribution and the observed carrier concentration profile. [Preview Abstract] |
Wednesday, March 16, 2016 1:51PM - 2:03PM |
L7.00012: Characterisation of potential barriers in a donor quantum dot defined by hydrogen resist lithography. Andreas Fuhrer, Nikola Pascher We use a four terminal donor quantum dot (QD) to characterize potential barriers between degenerately doped nanoscale contacts. The QD is fabricated by hydrogen resist lithography on Si(001) in combination with n-type doping from the gas-phase. The four contacts have different separations (d = 9, 12, 16 and 29 nm) to a central 6 nm x 6 nm island, leading to different tunnel- and capacitive coupling. We use cryogenic transport measurements in the Coulomb blockade regime to simultaneously probe current flow in the four terminals for various voltage configurations. The magnitude of the measured tunnelling currents as a function of applied bias and contact separation sets a limit of about 15 nm for tunnelling contacts and shows a strong increase of the barrier transmission with applied bias. Using a constant interaction picture we extract the mutual capacitances between the QD and the four contacts which are found to be in excellent agreement with numerically calculated values. Our results contribute to a better understanding of tunnelling barriers and gate electrodes in planar dopant devices and pave the way towards reliable quantum device fabrication at the atomic scale. [Preview Abstract] |
Wednesday, March 16, 2016 2:03PM - 2:15PM |
L7.00013: Nanoscale Imaging of Band Gap and Defects in Polycrystalline CdTe Photovoltaic Devices Nikolai Zhitenev, Yohan Yoon, Jungseok Chae, Aaron Katzenmeyer, Heayoung Yoon, Sangmin An, Joshua Shumacher, Andrea Centrone To further increase the power efficiency of polycrystalline thin film photovoltaic (PV) technology, a detailed understanding of microstructural properties of the devices is required. In this work, we investigate the microstructure of CdTe PV devices using two optical spectroscopies. Sub-micron thickness lamella samples were cut out from a PV device, either in cross-section or in-plane, by focused ion beam. The first technique is the photothermal induced resonance (PTIR) used to obtain absorption spectra over a broad range of wavelengths. In PTIR, a wavelength tunable pulsed laser is combined with an atomic force microscope to detect the local thermal expansion of lamella CdTe sample induced by light absorption. The second technique based on a near-field scanning optical microscope maps the local absorption at fixed near-IR wavelengths with energies at or below CdTe band-gap energy. The variation of the band gap throughout the CdTe absorber determined from PTIR spectra is $\approx $ 20 meV. Both techniques detect strong spatial variation of shallow defects over different grains. The spatial distribution of mid-gap defects appears to be more uniform. The resolution, the sensitivity and the applicability of these two approaches are compared. [Preview Abstract] |
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