Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session L28: Dopants and Defects in Semiconductors VI: Compound and 2D SemiconductorsFocus
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Sponsoring Units: DMP FIAP DCOMP Chair: Leigh Weston, University of California, Santa Barbara Room: 291 |
Wednesday, March 15, 2017 11:15AM - 11:51AM |
L28.00001: Single Quantum Defects in h-BN and ZnO Invited Speaker: Nicholas R Jungwirth Isolated point defects in wide bandgap semiconductors are single photon sources with applications in quantum optics, precision sensing, and quantum information processing technologies. Although the nitrogen-vacancy center in diamond has garnered the most attention, efforts to discover novel defect-based single photon sources have uncovered promising candidates in SiC, ZnO, and hexagonal boron nitride (h-BN). I will discuss our progress on identifying and characterizing isolated defects in ZnO and hBN. First I will report confocal fluorescence measurements of isolated defects in ZnO that exhibit single photon emission when excited by sub-bandgap energy light. Single-defect absorption (emission) polarization measurements reveal the presence of a single absorption (emission) dipole as opposed to multiple dipoles. We find that the absorption and emission dipoles are aligned parallel to one another within experimental uncertainty. Lastly, we analyze these polarization spectroscopy measurements in the context of point group theory. This approach enables us to infer the allowed symmetry properties of the defect's ground and excited state wavefunctions for several possible spatial symmetries common to the ZnO wurtzite lattice. Next I will discuss the distribution and temperature-dependent optical properties of zero-phonon emission from isolated defects in h-BN flakes. We observe sharp, single-photon emission lines distributed across an energy range that exceeds 500 meV. We also present a detailed study of the temperature-dependent linewidth, spectral energy shift, and intensity for two different zero-phonon lines centered at 575 nm and 682 nm. Our temperature-dependent results are well described by a lattice vibration model that considers piezoelectric coupling to phonons in the defect's particular two-dimensional h-BN sheet. [Preview Abstract] |
Wednesday, March 15, 2017 11:51AM - 12:03PM |
L28.00002: Theoretical studies of the magnetic properties of Mn trimers on the (110) GaAs surface Fhokrul Islam, Reza Mahani, Davide Grossi, Paul Koenraad, Carlo Canali Transition-metal impurity-doped GaAs has been the most intensively studied prototypical model system for understanding the magnetic properties of dilute magnetic semiconductors (DMS). While the study of isolated pairs of impurity provides insight about the nature of magnetic interactions in DMS, addressing larger clusters of magnetic impurities is essential for realizing complex magnetic phenomena such as spin frustration, spin-electric coupling and spin waves, which can be used in quantum information storage and processing. In this work, motivated in part by ongoing scanning tunneling spectroscopy (STM) experiments, we have investigated theoretically the electronics and magnetic properties of different Mn trimer configurations on the (110) surface of GaAs, using first-principles density functional theory (DFT) and microscopic tight-binding (TB) methods. We have employed DFT to study the physical stability and magnetic ground states for both collinear and triangular trimers and their dependence on crystallographic axes. The TB calculations, carried for some of the most stable Mn trimer configurations on the GaAs surface, yield information on the electronic structure and the local density of states associated with the Mn acceptor holes, which is directly probed in STM measurements. [Preview Abstract] |
Wednesday, March 15, 2017 12:03PM - 12:15PM |
L28.00003: Nuclear quantum effects at metal-insulator transition of (Ga,Mn)As Hannes Raebiger, Soungmin Bae Ga$_{1-x}$Mn$_x$As exhibits a Mott transition at the Mn concentration of $x_{\rm crit}\approx1\%$. We carry out self-interaction corrected density-functional calculations for this concentration regime, and in the find an insulator ground state $I$ for $x<0.5\%$, and a metal ground state $M$ for $x>1\%$. At $x=0.93\%$, however, $I$ and $M$ appear on a double well adiabatic potential energy curve, being separated only by a small energy barrier. Solving the Schr\"odinger eq.\ for nuclear motion along this adiabatic potential shows that, this energy barrier is smaller than the zero-point nuclear oscillations, i.e., the ground state must be described by the non-adiabatic superposition wavefunction $\Phi = c_M(Q;x) \phi^M + c_I(Q;x)\phi^I$, where $\phi^M$ and $\phi^I$ are the metallic and insulator states, respectively, and the expansion coefficients depend both on nuclear co-ordinates $Q$ and Mn concentration $x$. This implies that the Mott transition occurs continuously via a series of {\em excitonic phases}, as suggested by Kohn,\footnote{Kohn, Phys. Rev. Lett. {\bf 19}, 789 (1968).} but with the exception that the excitonic phase superposition states (charge density waves) can only be described after inclusion of nuclear quantum effects. [Preview Abstract] |
Wednesday, March 15, 2017 12:15PM - 12:27PM |
L28.00004: Magnetic interactions in Mn assemblies in a GaAs (110) surface. Paul Koenraad, Davide Grossi, Fhokrul Islam, Reza Mahani, Carlo Canali, Michael Flatt\'e We have used Scanning Tunneling Microscopy to create and study the electronic properties of dedicated assemblies of magnetic atoms in a semiconductor. We have been able to create pairs, trimers and tretramers of Mn atoms in the surface layer of GaAs. The electronic interaction between the Mn atoms in these structures is found to be highly anisotropic. We observed only for Mn pairs in the [110] direction a magnetic coupling. This observation is in contrast with previous experimental results [1], where substantial Mn-Mn interaction has been reported for pairs in additional directions. Our energy and spatial resolution allowed for a deeper analysis that showed that the influence of the surface on the anisotropic Mn-Mn magnetic interaction is correctly captured in the model presented in [2]. [1] D. Kitchen et al Nature 442, 436-439 (2006) [2] T.O. Strandberg et al, PRB 81, 054401 (2010). [Preview Abstract] |
Wednesday, March 15, 2017 12:27PM - 12:39PM |
L28.00005: Generalized Multiband Typical Medium Dynamical Cluster Approximation: Application to (Ga,Mn)N Yi Zhang, Ryky Nelson, Elisha Siddiqui, Kaming Tam, Unjong Yu, Tom Berlijn, Wei Ku, Vidhyadhiraja Sudhindra, Juana Moreno, Jarrell Mark We generalize the multiband typical medium dynamical cluster approximation and the formalism introduced by Blackman,
Esterling and Berk so that it can deal with localization in multiband disordered systems with
both diagonal and off-diagonal disorder with complicated potentials. We also introduce a new ansatz
for the momentum resolved typical density of states that greatly improves the numerical
stability of the method, while preserving the independence of scattering events at different frequencies.
Starting from the first-principles effective Hamiltonian, we apply this method to the
diluted magnetic semiconductor Ga$_{1-x}$Mn$_x$N, and find the impurity band is
completely localized for Mn concentrations $x<0.03$, while for $0.03 |
Wednesday, March 15, 2017 12:39PM - 12:51PM |
L28.00006: TEM-EELS Investigation of Boron and Phosphorus Passivated 4H-SiC/SiO$_{2}$ Interface Structures Christopher Klingshirn, Joshua Taillon, Gang Liu, Sarit Dhar, Leonard Feldman, Tsvetanka Zheleva, Aivars Lelis, Lourdes Salamanca-Riba A high density of electronic defects at the SiC/SiO$_{2}$ interface adversely affects SiC-based metal oxide semiconductor devices. Various treatments are known to improve device performance. Annealing in a nitric oxide (NO) environment, for example, passivates electronic defects at the interface and raises the carrier mobility in the active region to 35-40 cm$^{2}$/Vs, but the effect saturates after about 60 minutes of annealing.$^{1}$ Passivation with phosphorus$^{2}$ or boron$^{3}$ improves upon NO by a factor of 2, increasing the mobility to over 90 cm$^{2}$/Vs.$^{2}$ We investigate the chemical and structural effects of these treatments on the SiC/SiO$_{2}$ transition layer using high-resolution transmission electron microscopy (HRTEM) and high angle annular dark field (HAADF). Electron energy loss spectroscopy Spectrum Imaging (EELS SI) collected across the transition region allow identification of the width, composition and types of bonding at the transition layer. Advanced machine learning techniques applied to the EELS data reveal intermediate bonding states within this region. $^{1}$J. Taillon et al., J. Appl. Phys. 113, 044517 (2013). $^{2}$D. Okamoto et al., IEEE Electron Device Lett. 31, 710 (2010). $^{3}$D. Okamoto et al., IEEE Electron Device Lett. 35, 1176 (2014). [Preview Abstract] |
Wednesday, March 15, 2017 12:51PM - 1:03PM |
L28.00007: Investigation of 3C-SiC/SiO$_{\mathrm{2}}$ interfacial point defects from ab initio g-tensor calculations and electron paramagnetic resonance measurements T. A. Nugraha, M. Rohrmueller, U. Gerstmann, S. Greulich-Weber, A. Stellhorn, J. L. Cantin, J. von Bardeleben, W. G. Schmidt, S. Wippermann SiC is widely used in high-power, high-frequency electronic devices. Recently, it has also been employed as a building block in nanocomposites used as light absorbers in solar energy conversion devices. Analogous to Si, SiC features SiO$_{\mathrm{2}}$ as native oxide that can be used for passivation and insulating layers. However, a significant number of defect states are reported to form at SiC/SiO$_{\mathrm{2}}$ interfaces, limiting mobility and increasing recombination of free charge carriers. We investigated the growth of oxide on different 3C-SiC surfaces from \textit{first principles}. Carbon antisite Csi defects are found to be strongly stabilized in particular at the interface, because carbon changes its hybridization from sp$^{\mathrm{3}}$ in the SiC-bulk to sp$^{\mathrm{2}}$ at the interface, creating a dangling bond inside a porous region of the SiO$^{\mathrm{2}}$ passivating layer. Combining \textit{ab initio} g-tensor calculations and electron paramagnetic resonance (EPR) measurements, we show that Csi defects explain the measured EPR signatures, while the hyperfine structure allows to obtain local structural information of the oxide layer. Financial support from BMBF NanoMatFutur grant 13N12972 and DFG priority program SPP-1601 is gratefully acknowledged. [Preview Abstract] |
Wednesday, March 15, 2017 1:03PM - 1:15PM |
L28.00008: Electronic structure properties of deep defects in hBN Pratibha Dev In recent years, the search for room-temperature solid-state qubit (quantum bit) candidates has revived interest in the study of deep-defect centers in semiconductors. The charged NV-center in diamond is the best known amongst these defects. However, as a host material, diamond poses several challenges and so, increasingly, there is an interest in exploring deep defects in alternative semiconductors such as hBN. The layered structure of hBN makes it a scalable platform for quantum applications, as there is a greater potential for controlling the location of the deep defect in the 2D-matrix through careful experiments. Using density functional theory-based methods, we have studied the electronic and structural properties of several deep defects in hBN. Native defects within hBN layers are shown to have high spin ground states that should survive even at room temperature, making them interesting solid-state qubit candidates in a 2D matrix. [Preview Abstract] |
Wednesday, March 15, 2017 1:15PM - 1:27PM |
L28.00009: Evolution of electronic structure in highly charge doped MoS2 compounds Mohammed Bin Subhan, Matthew Watson, Zhongkai Liu, Andrew Walters, Moritz Hoesch, Chris Howard Transition-metal dichalcogenides (TMDCs) are a group of layered materials that exhibit a rich array of electronic ground states including semiconductivity, metallicity, superconductivity and charge density waves. In recent years, 2D TMDCs have attracted considerable attention due to their unique properties and potential applications in optoelectronics. It has been shown that the charge carrier density in few layer MoS2 can be tunably increased via electrostatic gating. At high levels of doping, MoS2 exhibits superconductivity with a “dome-like” dependence of Tc on doping analogous to that found in the cuprate superconductors. High doping can also be achieved via intercalation of alkali metals in bulk MoS2. The origin of this superconductivity is not yet fully understood with predictions ranging from exotic pairing mechanisms in bulk systems to Ising superconductivity in single layers. Despite these interesting properties, there has been limited research to date on the electronic structure of these doped compounds. Here we present our work on alkali metal intercalated MoS2 using the low temperature metal ammonia solution method. Using X-ray diffraction, Raman spectroscopy and ARPES measurements we will discuss the physical and electronic structure of these materials. [Preview Abstract] |
Wednesday, March 15, 2017 1:27PM - 1:39PM |
L28.00010: A universal parametric representation for weak-localization magnetoconductance in 2D and 3D systems Guy Matmon, Eran Ginossar, Byron Villis, Alex Kölker, Tingbin Lim, Neil Curson, Juerong Li, Ben Murdin, Andrew Fisher, Gabriel Aeppli We study the magnetotransport properties of a heavily-doped Si:P 2D layer, as a step towards the fabrication of buried ordered dopant structures and wires. The magnetoconductance $\Delta\sigma$ is dominated by weak localization. A combination of linear and angular magnetic field sweeps reveals the existence of a single dimensionless parameter $p$, which governs the magnitude of $\Delta\sigma$ as a function of magnetic field magnitude and inelastic scattering length (which is temperature dependent). We compare this with weak localization in bulk Si:P and find that even though the magnetic-field dependence of $\Delta\sigma$ is logarithmic in 2D and power-law in 3D, their dependence on $p$ is unchanged, thus establishing a universal behavior that is independent of dimension. [Preview Abstract] |
Wednesday, March 15, 2017 1:39PM - 1:51PM |
L28.00011: First-principles study of the effects of Silicon doping on the Schottky barrier of TiSi$_{2}$/Si interfaces Han Wang, Eduardo Silva, Damien West, Yiyang Sun, Oscar Restrepo, Shengbai Zhang, Murali Kota As scaling of semiconductor devices is pursued in order to improve power efficiency, quantum effects due to the reduced dimensions on devices have become dominant factors in power, performance, and area scaling. In particular, source/drain contact resistance has become a limiting factor in the overall device power efficiency and performance. As a consequence, techniques such as heavy doping of source and drain have been explored to reduce the contact resistance, thereby shrinking the width of depletion region and lowering the Schottky barrier height. In this work, we study the relation between doping in Silicon and the Schottky barrier of a TiSi$_{2}$/Si interface with first-principles calculation. Virtual Crystal Approximation (VCA) is used to calculate the average potential of the interface with varying doping concentration, while the I-V curve for the corresponding interface is calculated with a generalized one-dimensional transfer matrix method. The relation between substitutional and interstitial Boron and Phosphorus dopant near the interface, and their effect on tuning the Schottky barrier is studied. These studies provide insight to the type of doping and the effect of dopant segregation to optimize metal-semiconductor interface resistance. [Preview Abstract] |
Wednesday, March 15, 2017 1:51PM - 2:03PM |
L28.00012: Two-dimensional massless Dirac fermions and Fermi level matching with Dirac points in alkaline-metal doped few-layer black phosphorus Seung Su Baik, Young-Woo Son, Hyoung Joon Choi Since the inception of atoms-thick black phosphorus (BP) in 2014, bandgap tuning of BP has been one of the central issues in BP-based field-effect-transistors and optoelectronic devices. As other layered materials held by van der Waals forces, BP bandgap is modulated by the control of layer thickness and external perturbations such as strain and electric field. Recently, BP bandgap was shown to be fine-tuned by the simple method of potassium (K) doping on the BP surface [1,2]. Marked physical properties of K doped BP are summarized as the emergence of two-dimensional (2D) massless Dirac fermions and its stability with respect to the spin-orbit interaction. However, for the practical use of K doped BP in actual devices, the location of emerged Dirac points is required to be shifted-back to around the Fermi level. In this talk, based on first-principles calculations, we report the shift-back method of Dirac points by means of various co-dopings, and the distribution of alkaline-metal atoms on the BP surface. The switchable massless Dirac fermions discussed here may open a new way for the development of high performance devices in 2D materials beyond graphene. [1] J. Kim et al, Science \textbf{349}, 723-725, (2015). [2] S. S. Baik et al, Nano Lett. \textbf{15}, 7788-7793 (2015). [Preview Abstract] |
Wednesday, March 15, 2017 2:03PM - 2:15PM |
L28.00013: Pinning of topological solitons at extrinsic defects in a quasi one-dimensional charge density wave Samad Razzaq, Stefan Wippermann Quasi one-dimensional (1D) electronic systems are known to exhibit exotic physical phenomena, such as, e.g., Jahn Teller distortions, charge density wave (CDW) formation and non-Fermi liquid behavior. Solitonic excitations of the charge density wave ordered ground state and associated topological edge states in atomic wires are presently the focus of increasing attention. We carried out a combined \textit{ab initio} and scanning tunneling microscopy (STM) study of solitonic and non-solitonic phase defects in the In/Si(111) atomic wire array. While free solitons move too fast to be imaged directly in STM, they can become trapped at extrinsic de- fects within the wire. We discuss the detailed atomistic structure of the responsible extrinsic defects and trapped solitons. Our study highlights the key role of coupled theory-experimental investigations in order to understand also the elusive fast moving solitons. S. W. gratefully acknowledges financial support from the German Research Foundation (DFG), grant No. FOR1700. [Preview Abstract] |
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