Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q12: Focus Session: Dopants and Defects in Semiconductors: Conducting Oxides |
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Sponsoring Units: DMP Chair: Joel Ager, Lawrence Berkeley National Laboratory Room: D223/224 |
Wednesday, March 23, 2011 11:15AM - 11:51AM |
Q12.00001: Transparent Conductors: Understanding and Optimization Invited Speaker: The unique combination of two mutually exclusive properties -- optical transparency and electrical conductivity -- is known to be a prerogative of only a few oxides of post-transition metals, namely, In$_2$O$_3$, ZnO, CdO and SnO$_2$. Advances in theoretical understanding of the underlying physical phenomena in conventional transparent conducting oxides (TCOs) and rapid development of the technologies for which TCO is a vital component, stimulate further research aimed at (i) broadening the range of the electronic and optical properties of application-specific transparent conductive materials in a controllable way; (ii) improving the functional capabilities and efficiency of TCOs in a device; and (iii) designing novel materials as a viable, inexpensive alternative to conventional TCOs. Here, we employ first-principles density-functional approach to investigate the structural, electronic and optical properties of several classes of transparent conductors including conventional single-cation main-group oxides, multi-component binary and ternary oxides, as well as several non-oxide materials. Systematic comparative investigations allow us to determine the role of the crystal structure, chemical composition and carrier generation mechanisms on the resulting optical and electronic properties and predict ways to optimize the properties. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q12.00002: Origins of superior symmetrical doping ability of monoclinic BiVO4 Yanfa Yan, Wan-Jian Yin, Su-Huai Wei, Mowafak Al-Jassim, John Turner Application of semiconductors for functional devices depends critically on their dopability. However, there are strong doping bottlenecks for wide-band-gap semiconductors -- symmetrical doping is usually difficult, which severely restrict their potential applications. Here, we report superior symmetrical doping properties, i.e., $n$-type and $p$-type, of monoclinic BiVO$_{4}$ by first-principles density-functional theory calculation. Our results reveal that without external doping, BiVO$_{4}$ with moderate $n$-type and $p$-type conductivities can be obtained. However, doping of Sr, Ca, Na, and K atoms under oxygen-rich growth conditions can lead to outstanding $p$-type conductivity, whereas doping of Mo and W under oxygen-poor growth conditions can result in excellent $n$-type conductivity. We find that Bi 6s state is responsible for the good p-type doping and the presence of V 3d state is responsible for the good n-type doping. Furthermore, the Bi $6s$ and V 3$d$ states are also responsible for producing very dispersive valence and conduction band edges, leading to small electron and hole effective masses. The superior symmetrical doping properties and high carrier mobility make BiVO$_{4}$ a promising candidate for electronic and optoelectronic device applications. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q12.00003: Donors and H impurities in SnO$_{2}$ studied by IR spectroscopy Figen Bekisli, Michael Stavola, W. Beall Fowler, Lynn Boatner, Erik Spahr, Gunter Luepke Theory predicts that SnO$_{2}$ is an attractive wide band gap candidate for achieving p-type conductivity. Interstitial H and H$_{O}$ are suggested to be shallow donors in SnO$_{2}$ [1-3]. We have studied the properties of H in SnO$_{2}$ single crystals. An O-H line is observed at 3261 cm$^{-1}$ that is polarized perpendicular to the c direction along with weaker features at 3258 and 3272 cm$^{-1}$. When D is introduced into SnO$_{2}$ by annealing in a D$_{2}$ ambient at 700\r{ }C, a variety of new O-H and O-D lines is produced along with the low-frequency absorption that is characteristic of free carriers. To probe the relationship between H and the free carriers it introduces, we have examined the thermal stabilities of the O-H and O-D lines and their relationship to the thermal stability of the free-carrier absorption. \\[4pt] [1] A.K. Singh \textit{et al}., Phys. Rev. Lett. \textbf{101}, 055502 (2008). \\[0pt] [2] J.B. Varley \textit{et al.,} Phys. Rev. B \textbf{79}, 245206 (2009). \\[0pt] [3] W.M. Hlaing Oo \textit{et al.}, Phys. Rev. B \textbf{82}, 193201 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q12.00004: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q12.00005: Asymmetric Cation stoichiometry in Spinels : Site occupancy in Co$_{2}$ZnO$_{4}$ and Rh$_{2}$ZnO$_{4}$ Tula Paudel, S. Lany, A. Zunger, A. Sigdel, A. Zakutayev, J. Perkins, D. Ginley, J. Bettinger, Y. Shi, M. Toney, A. Nagaraja, N. Perry, T. Mason Cations A and B in A$_{2}$BX$_{4}$ spinels normally appear in precise 2:1 Daltonian ratio only at low temperature. At finite temperature, they become either A-rich or B-rich, which control dopability of the compound. We survey the experimentally observed stoichiometry asymmetries and describe the first principles framework for calculating these. The results of the calculations compare well with the phase boundary determined from XRD and the site occupancy measured by anomalous-XRD on Co$_{2}$ZnO$_{4}$ and Rh$_{2}$ZnO$_{4}$ samples grown in thermodynamic equilibrium. Good comparison between theory and experiment allows us predict the co-existence line in composition range form first principle for other spinels, which in turn can be extended to predict the nature of electrical conductivity of a compound, while designing the material with the desired properties via principle of inverse design. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q12.00006: Dopants and defects in conductive oxide spinels Andriy Zakutayev, John Perkins, Phillip Parilla, Tula Paudel, Staphan Lany, David Ginely, Alex Zunger We will discuss the effects of extrinsic and intrinsic imperfections (dopants and defects) in a group of conductive oxide materials related to Co3O4. Co3O4 is a spinel with Co2+ and Co3+ on tetrahedral and octahedral sites, respectively. Doping of Co3O4 with Zn and Ni represent two limiting cases: Zn2+ ions have a preference to occupy tetrahedral (Co2+) sites and are predicted to be unable to dope effectively; Ni2+ ions have a preference to occupy octahedral (Co3+) sites, so these atoms are expected to be efficient dopants. We found that substitution of Co3O4 spinel with up to 33 percent of Zn and Ni results in formation of ZnCo2O4 normal spinel and NiCo2O4 inverse spinel, and causes 100-fold and 1000-fold increases in conductivity, respectively, matching the predicted trend. Increase in Zn and Ni concentraion up to 40 percent cause phase separation of ZnO and NiO and leveling out of the conductivity. The conductivity decreases sharply above 50-60 percent Zn and Ni substitution level. Small differences with the theoretical predictions may be explained by non-equilibrium character of the thin film deposition process. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q12.00007: Possible \textit{n}-type carrier producers in In$_2$O$_3$(ZnO)$_k$ homologous compounds Haowei Peng, Jung-Hwan Song, Arthur J. Freeman In$_2$O$_3$(ZnO)$_k$ (${\rm k = integers}$) homologous compounds are promising intrinsic \textit{n}-type transparent conducting semiconductors.\footnote{T. Moriga, et.al., J. Am. Ceram. Soc. \textbf{81}, 1310 (1998).} To find out the carrier producers, we investigated the energetics and thermodynamic properties of \textit{n}-type defects and their complexes in In$_2$O$_3$(ZnO)$_k$, with the k=3 phase as prototype, using the first-princiles density functional method. We calculated the defect formation energies and defect transition energy levels of oxygen vacancies (V$_{\rm O}$), substitutional indium on zinc sites (In$_{\rm Zn}$), zinc and indium interstitials (Zn$_i$ and In$_i$) on different atomic sites, and also some V$_O$--In$_{\rm Zn}$ and V$_{\rm O}$--Zn$_i$ defect complexes. We find, under the experimental growth condition of O-poor and $T=1300$$^{\circ}$C, that V$_{\rm O}$, In$_{\rm Zn}$, and V$_{\rm O}$-In$_{\rm Zn}$ complexes have much lower formation energies than the others, among which V$_{\rm O}$ will stay in the neutral charged state and the latter two are the most possible \textit{n}-type carrier producers. The V$_{\rm O}$-In$_{\rm Zn}$ complex tends to form between V$_{\rm O}$ and In$_{\rm Zn}$ in the same atomic layer; thus its distribution should be affected by the site-preference of V$_{\rm O}$. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q12.00008: Protonic motion in Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$ thin films and its implications on resistance change properties Mihir Tendulkar, Nicholas Breznay, Yoshio Nishi Thin films of Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (PCMO) exhibit resistance-change properties that are of acute interest for next-generation memory solutions. Recent work has demonstrated that oxidation / reduction of a reactive electrode is critical to the switching process, suggesting that interface engineering will solve the reliability issue. We show that an overlooked contributor to the process is hydrogen, which dopes the bulk film. Activated conduction and loss tangent measurements are correlated with FTIR spectra to demonstrate protonic motion through the repeated breaking and reforming of --OH bonds. SIMS and Hall measurements are presented in conjunction with UV-Vis spectroscopy to show that hydrogen also alters the electronic structure of the PCMO film. The implications of these effects on forming and switching are discussed. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q12.00009: Dynamics of Interstitial H in TiO$_{2}$ W.B. Fowler, A. Murphy, M. Stavola H transport in rutile TiO$_{2}$ is important because of the low energy barriers within the open lattice in the c-direction [1]. As part of a study of the dynamics of interstitial H, potential energy functions for the vibration of hydrogen between two cross-channel O were generated. Double-well functions were modeled using experimental data [2] for the fundamental stretching vibrational frequencies of the three isotopes of H along with theoretical information obtained from quantum-mechanical calculations using [3] CRYSTAL06. These functions were then used to predict where the first overtone may lie, and its relative transition probability. The unexpectedly large anharmonicity observed for the OH vibration is correlated with the hydrogen-bond nature of the O-H ----O potential.\\[4pt] [1] O. W. Johnson et al., J. Appl. Phys. 46, 1026 (1975); J. B. Bates et al., Phys. Rev. B 19, 4130 (1979); E. J. Spahr et al., Phys. Rev. Lett. 104, 205901 (2010).\\[0pt] [2] J. B. Bates and R. A. Perkins, Phys. Rev. B 16, 3713 (1977).\\[0pt] [3] R. Dovesi et al., Crystal06 User's Manual, Univ. of Torino, Torino, 2006. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q12.00010: Interstitial and substitutional Zr in SrTiO3 John Jaffe, Renee Van Ginhoven, Weilin Jiang We investigate Zr in SrTiO$_{3}$ (STO) as an electronic dopant and as a model for nuclear waste forms in which radioactive Sr decays to Y and then to stable Zr through beta emission. Density functional theory (DFT) within the supercell model is used to predict the thermodynamic stability and electronic states of interstitial and Sr- or Ti-substituted Zr atoms in the STO lattice. Native point defects such as vacancies and antisites are also considered. When Zr replaces Sr, its most stable configuration is to simply occupy the Sr site (instead of, for example, replacing a Ti and displacing the Ti to the Sr site.) For Zr added to the lattice, its most stable configuration is to replace a Ti, making a Zr$_{Ti}$ impurity plus a Ti interstitial (as opposed to the Zr just remaining as an interstitial atom.) Zr$_{Sr}$ is predicted to be a double electron donor, Zr$_{Ti}$ is electrically inactive and interstitial Zr and Ti are predicted to be quadruple donors, with all donor levels in the conduction band. Zr$_{Sr}$ and the tetravalent interstitials are all predicted to increase the crystal volume, and the interstitials also are predicted to lead to a tetragonal distortion of the lattice. Experiments with injection of Zr atoms into STO qualitatively confirm these predictions of crystal structural changes. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q12.00011: ABSTRACT WITHDRAWN |
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