Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session P18: Surfaces and Point Defects in Semiconductor |
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Sponsoring Units: DCMP Chair: Dr. Tae-Sik Yoon, Dept. MSE, UCLA Room: LACC 406A |
Wednesday, March 23, 2005 11:15AM - 11:27AM |
P18.00001: Improved Simulation of Charged Defect Profiles in Scanning Tunneling Microscopy Images Geoffrey W. Brown, Marilyn E. Hawley Scanning tunneling microscopy is often used to study charged defects at semiconductor surfaces. Charge-induced band bending affects the local tunnel current by changing the electronic state density between tip and sample Fermi levels. Imaging is usually carried out under constant current feedback conditions with adjustable tip-sample spacing and a constant tunnel gap voltage. In order to understand the defects, surface profiles through the defect screening regions are often simulated using either standard tunneling theory or a scattering theory approach. These produce qualitative agreement with observations but could be improved by using a more accurate form of the electrostatic potential and by self-consistently calculating the band bending, screening length, and resulting tip response under constant current conditions at each point along the profile. We have done this calculation for the tunneling theory approach. We will describe the details of the calculation and then show the results of applying it to charged features near GaAs(110) surfaces. [Preview Abstract] |
Wednesday, March 23, 2005 11:27AM - 11:39AM |
P18.00002: Dimer and NEB studies on Si $I_{4}$ chain and the ground state $I_{4}$ Yaojun Du, John Wilkins The dimer method explores the energy landscape of two important Si four-interstitials: 1) the ground state and 2) chain extending in the [110] direction. DFT-GGA calculations find the ground state is an extremely stable with 3.3-8.4 eV barrier to five dimer-identified neighboring minima. Those minima are 0.9-1.8 eV above the ground state. In contrast, the chain's most accessible local minimum has 1 eV barrier to the three-interstitial ground state plus a nearby single interstitial with a tiny 0.1 eV barrier to form chain. The tight-binding, nudged-elastic-band pathway from the chain to the four-interstitial ground state has two structurally close local minima with a separation of 4.4 \AA. The chain-to-ground-state barrier is 1.4 eV, suggesting that the tri-interstitial could grab an interstitial to form a four-interstitial chain that could grow into a longer chain without falling into the four interstitial ground state. [Preview Abstract] |
Wednesday, March 23, 2005 11:39AM - 11:51AM |
P18.00003: Energy Scaling and Surface Patterning of Halogen-Terminated Si(001) Surfaces Duane D. Johnson, Nikolai Zarkevich We show that the steric repulsion energies between halogen dimers on a passivated Si(001) surface scale with square of the principle quantum number of the halogen, and arise mostly from bonding with Si substrate. We exemplify the scaling from previously calculated steric interactions of F, Cl, and Br, predict the interactions for I and At, and verify the prediction by density-functional calculations. From the energetics, we explain the patterning of the halogen-terminated Si(001), providing a better understanding of the halogen-roughening process, and predict a crossover to a new vacancy-line defect for large halogens. [Preview Abstract] |
Wednesday, March 23, 2005 11:51AM - 12:03PM |
P18.00004: Diffusion Monte Carlo Formation Energies of Silicon Self-Interstitial Defects Kevin P. Driver, William D. Parker, Phillip R. Peterson, Richard G. Hennig, John W. Wilkins, Cyrus J. Umrigar Silicon self-interstitial defects can hinder the fabrication of semiconductor devices. Several stable single-, di-, and tri-interstitial clusters found with \emph{ab initio} and tight-binding simulations are believed to form in silicon\footnote{D. A. Richie et al. \emph{Phys. Rev. Lett}. \textbf{92}, 45501 (2004).}. Since experimental detection of self-interstitials remains a challenge, accurate theoretical methods are needed to study their properties. The first Diffusion Monte Carlo (DMC) calculations found single-interstitial defect formation energies to be about 1 eV higher than predicted by density functional theory (DFT)\footnote{W.-K. Leung et al. \emph{Phys. Rev. Lett.} \textbf{83}, 2351 (1999).}. This indicates that DFT may be insufficient for the study of silicon self-intersitials. We confirm the discrepancy between DMC and DFT formation energies for three single-interstitial structures (X, H, and T) and extend the comparison to several di- and tri-interstitial clusters. [Preview Abstract] |
Wednesday, March 23, 2005 12:03PM - 12:15PM |
P18.00005: Interactions between native point defects in ZnGeP$_2$. Xiaoshu Jiang, M. S. Miao, Walter R. L. Lambrecht First-principles calculations of the native point defects $V_{Zn}$, $V_{Ge}$, $Zn_{Ge}$ and $Ge_{Zn}$ show that under Zn-poor conditions, the dominant defects are the $Ge_{Zn}$ and $V_{Zn}$. Since these are respectively a donor and an acceptor, one may expect them to attract each other. The formation of complexes of the type $V_{Zn}-Ge_{Zn}-V_{Zn}$ was studied and found to be favorable.A simple molecular model is proposed for the electronic structure of this complex. Optical excitation of electron paramagnetic resonance (EPR) studies by Gehlhoff et al. [1] were used by these authors to extract energy levels in the gap associated with these defects. The model proposed by these authors assumes that the $Ge_{Zn}$ EPR centrum in irradiated samples becomes activated by a two step process in which an electron from a $V_{Zn}^{2-}$ is optically excited to the conduction band and subsequently trapped at a $Ge_{Zn}^{2+}$ site converting the two defects in EPR active sites $V_{Zn}^-$ and $Ge_{Zn}^+$. We instead propose a direct transition between the two defect states without the intervening conduction band and show that our calculated occupation energy levels agree with such a model. The $V_{Ge}$ on the other hand is found to have a high energy formation and to be unstable towards the formation of a $V_{Zn}$ and a $Zn_{Ge}$ antisite. [1] W. Gehlhoff, R. N. Pereira, D. Azamat, A. Hoffmann, and N. Dietz, Physica B {\bf 308-310}, 1015 (2001). [Preview Abstract] |
Wednesday, March 23, 2005 12:15PM - 12:27PM |
P18.00006: Hartree-Fock Cluster Investigation of Locations for Erbium in Silicon Junho Jeong, R.H. Scheicher, N. Sahoo, M.B. Huang, T.P. Das, Lee Chow, S. Byahut, D.R. Mishra, M.M. Aryal, N.B. Maharjan, D.D. Paudyal Using the Hartree-Fock Cluster Procedure, we have investigated three locations hexagonal and tetrahedral interstitial (H$_{i}$ and T$_{i})$ and substitutional (S) for Er$^{3+}$ in Silicon including relaxation effects of the Si neighbors of Er$^{3+}$. Our results for the binding energies show that S is the most stable site for Er$^{3+}$, in contrast with the results from the most recent channeling measurements,\footnote{M. B. Huang et al., Appl. Phys. Lett. 81, 2734 (2002)} which can best be explained assuming that Er$^{3+}$ is at T$_{i}$ site. Possible reasons for the difference will be suggested. Magnetic hyperfine fields obtained for the Er nucleus at various sites will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 12:27PM - 12:39PM |
P18.00007: A LSDA+U Study on Bulk CuO: Electronic Structures and Native Defects Dangxin Wu, Qiming Zhang, Longcheng Wang, Meng Tao We have performed a first-principles study on the electronic structure and the formation of native defects in the monoclinic CuO by using the LSDA+U method with the PAW potentials. The optimized structural parameters of the crystal are in good agreement with the experimental data. The band structure of the crystal is calculated. An indirect band-gap of ~1.0 eV is obtained, which agree with the experimental semiconducting property of the material. This is qualitatively different from a LDA or LSDA calculation, which predicts a metal with the Fermi level below the top of valence band. The formation energies of various native defects as well as their charged states in CuO are carefully studied. The influence of Fermi level and the stoichiometry to the defects formation will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 12:39PM - 12:51PM |
P18.00008: Does the zinc vacancy in ZnGeP$_2$ exhibit a Jahn-Teller distortion? Walter R.L. Lambrecht, Xiaoshu Jiang, M.S. Miao, Sukit Limpijumnong The Zn-vacancy is one of the dominant defects in ZnGeP$_2$. Its single negative charge state is EPR active. The hyperfine splitting shows that the unpaired electron is primarily localized on a pair of P atoms. In contrast, first-principles 64 atom supercell calculations using both the FP-LMTO and the VASP method of the $V_{Zn}^{-}$ state show that the defect maintains $S_4$ symmetry with the wave function spread equally over 4 P atoms. Here a group-theoretical analysis is presented. When including only the nearest neighbors, the system has $D_{2d}$ symmetry. While the one electron state of the unpaired electron is non-degenerate, a doubly degenerate $e$-state lies only about 10 meV below it. We show that a P-pairing distortion mode splits this $e$-state in two states which are even with respect to one of the mirrorplanes and odd with respect to the other and thus can only contain two of the P-dangling bonds. Calculations in which a pairing of P atoms is enforced while relaxing the remaining atoms confirm this model. Remaining puzzling aspects of this defect will be discussed. [Preview Abstract] |
Wednesday, March 23, 2005 12:51PM - 1:03PM |
P18.00009: Study of the stability of Se passivation layers on Si(001) surfaces using time-of-flight positron annihilation induced Auger electron spectroscopy J. Zhu, Manori Nadesalingam, A. H. Weiss, Meng Tao The stability of Se passivation layers on a Si(001) surface was investigated using a non-destructive surface sensitive technique: Time-of-Flight Positron annihilation induced Auger Electron Spectroscopy (TOF-PAES). After 10 days of exposure in the air, the Se passivation layer was observed to incorporate some oxygen but to remain largely intact. Part of the adsorbed oxygen was removed during annealing at 400\r{ }C in the UHV-environment, however, some oxygen remained on the surface until high temperature annealing at 1030\r{ }C. We posit that that the oxygen that remained after the low temperature anneal was chemisorbed on the Si at defects in the Se passivation layer. The Se passivation layer was stable up to an annealing temperature of $\sim $ 800\r{ }C. The stability of the Se-passivated Si(001) surface is attributed to the saturation of the Si dangling bonds at the surface and to the strong Se-Si bonds. [Preview Abstract] |
Wednesday, March 23, 2005 1:03PM - 1:15PM |
P18.00010: Uniaxial stress study of the ro-vibrational transitions of HD in Si G. A. Shi, M. Stavola, W. B. Fowler, E. E. Chen The vibrational spectroscopy of interstitial H$_{2}$ in Si gave rise to a number of perplexing puzzles that concerned the rotational motion of the defect [1]. Most experiments were interpreted in terms of a static defect whereas theory suggested that there should be a very small barrier to rotation. The position and intensity of the HD vibrational line were also anomalous. The key to the solution of these puzzles was the discovery of a new vibrational line for HD and the recognition that certain ro- vibrational transitions are possible for HD that are not possible for the H$_{2}$ or D$_{2}$ homonuclear molecules in Si. H$_{2}$ in Si is a nearly free rotator after all. New experiments have been performed for HD in Si in which IR spectroscopy combined with uniaxial stress has been used to confirm the assignments of the ro-vibrational transitions of HD that underpin our understanding of H$_{2}$ in Si. This work is supported by NSF Grant DMR 0403641. 1. M. Stavola, E E. Chen, W.B. Fowler, G.A. Shi, Physica B \textbf{340-342}, 58 (2003), and references contained therein. [Preview Abstract] |
Wednesday, March 23, 2005 1:15PM - 1:27PM |
P18.00011: B couples formation and dissolution in ion implanted Si. Emanuele Rimini, Lucia Romano, Alberto Piro, Maria Grazia Grimaldi The off-lattice displacement of electrically active, substitutional B in presence of Si interstitials generated by light ion irradiation has been studied by channeling along the $<$100$>$ and $<$110$>$ axes. The channeling yield $\chi $ of B increases with the ion fluence until it saturates at $\chi \approx $ 0.5 suggesting a non-random B displacement. At the saturation B is not electrically active and accurate angular scans indicates the formation of B-B couples aligned along the $<$100$>$ direction in agreement with first principle calculations. The same kind of defect is formed upon B implantation at room temperature as demonstrated also by angular scans with $\chi _{B}\approx $0.5. A peculiar behavior is observed upon annealing: at 800 \r{ }C a significant increase of randomly located B occurs and $\chi _{B}\approx $1, at higher temperatures B recovers progressively into substitional site. The $\chi _{B}$ reaches 0.1 at 950 \r{ }C and the carrier concentration coincides with the amount of substitutional B. The increase of $\chi _{B}$ at 800\r{ }C can be due to the dissolution of B couples and to an intermediate off lattice location of B before to occupy a substitutional site. [Preview Abstract] |
Wednesday, March 23, 2005 1:27PM - 1:39PM |
P18.00012: Scanning Probe Study of Donor Layer Charging in a Gallium Arsenide Heterostructure Irma Kuljanishvili, Stuart Tessmer, Loren Pfeiffer, K.W. West We use a cryogenic scanning probe technique to study the charging behavior of silicon dopants in a GaAs/AlGaAs heterostructure sample. The sample contains a delta doped layer which is 60 nm below the exposed surface and 20 nm above an underlying two-dimensional electron system. We locally induce charge to enter the donor layer by applying an ac excitation voltage to a sharp metal tip situated a few nanometers above the surface. The resulting image charge appearing on the tip provides a local measure of magnitude of charge entering the donor layer. Here we report measurements as a function of dc voltage and magnetic field. [Preview Abstract] |
Wednesday, March 23, 2005 1:39PM - 1:51PM |
P18.00013: Si as an acceptor in (110) GaAs for high mobility p-type heterostructures F. Fischer, M. Grayson, D. Schuh, M. Bichler, G. Abstreiter, K. Neumaier We implement metallic layers of Si-doped (110) GaAs as modulation doping in high mobility p-type heterostructures, changing to p-growth conditions for the doping layer alone. The strongly auto-compensated doping is first characterized in bulk samples, identifying the metal-insulator transition density and confirming classic hopping conduction in the insulating regime. To overcome the poor morphology inherent to Si p-type (110) growth, heterostructures are fabricated with only the modulation doping layer grown under p-type conditions. Such heterostructures show a hole mobility of $\mu = 1.75 \times10^5~ \textnormal{cm}^2/\textnormal{V}\textnormal{s}$ at density $p=2.4\times10^{11}~ \textnormal{cm}^{-2}$. We identify the zero field spin-splitting characteristic of p- type heterostructures, but observe a remarkably isotropic mobility and a persistent photoconductivity unusual for p- heterojunctions grown using other doping techniques. This new modulated growth technique is particularly relevant for p-type cleaved-edge overgrowth and for III-V growth chambers where Si is the only dopant. [Preview Abstract] |
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