A5080915325- Semiconductor materials and devices
- Electronic and Structural Properties of Oxides
- Ferroelectric and Piezoelectric Materials
- Magnetic and transport properties of perovskites and related materials
- Semiconductor materials and interfaces
- Ferroelectric and Negative Capacitance Devices
- Photonic and Optical Devices
- Photorefractive and Nonlinear Optics
- Advancements in Semiconductor Devices and Circuit Design
- Advanced Condensed Matter Physics
- Surface and Thin Film Phenomena
- Ga2O3 and related materials
- Electron and X-Ray Spectroscopy Techniques
- Catalytic Processes in Materials Science
- Advanced Materials Characterization Techniques
- Advanced Memory and Neural Computing
- Catalysis and Oxidation Reactions
- Silicon Nanostructures and Photoluminescence
- ZnO doping and properties
- Transition Metal Oxide Nanomaterials
- Advanced Chemical Physics Studies
- Multiferroics and related materials
- GaN-based semiconductor devices and materials
- Acoustic Wave Resonator Technologies
- Silicon and Solar Cell Technologies
The University of Texas at Austin
2016-2025
The University of Texas at Dallas
2017-2021
University of California, Santa Barbara
2021
University of California, Davis
2002-2021
Arizona State University
1994-2020
Rutgers, The State University of New Jersey
2020
Oak Ridge National Laboratory
2018
IBM Research - Thomas J. Watson Research Center
2014
New Mexico State University
2014
IBM Research - Almaden
2014
Abstract One of the outstanding advancements in electronic‐structure density‐functional methods is Sankey–Niklewski (SN) approach [Sankey and Niklewski, Phys. Rev. B 40 , 3979 (1989)]; a method for computing total energies forces, within an ab initio tight‐binding formalism. Over past two decades, several improvements to have been proposed utilized calculate materials ranging from biomolecules semiconductors. In particular, improved (called F IREBALL ) uses separable pseudopotentials goes...
We develop a theoretical electronic structure based approach suitable for the study of complex silicas, and apply it to three different silica polymorphs. The method is first principles but simplified cope with large systems. Charge transfer between ions included in self-consistent fashion. found be adequate describe relative energies used construct model energy structural transition high cristobalite. In addition we have studied moderately silica, melanophlogite. Melanophlogite, although...
The energetics and band structures of the elemental semiconductor Si in two fourfold-coordinated clathrate have been studied. For Si(34) Si(46) we predict indirect gaps near 1.9 eV, or 0.7 eV wider than that well-known ${\mathit{sp}}^{3}$ diamond structure. We find energy differences between structure are about 0.07 which is nearly three times smaller those for more compact high-pressure Si. calculations done using an ab initio tight-binding-like molecular-dynamics method, further checked by...
Improvements to the Sankey-Niklewaki method [O. F. Sankey and D. J. Niklewski, Phys. Rev. B 40, 3979 (1989)] for computing total energies forces, within an ab initio tight-binding formalism, are presented here. In particular, improved (called FIREBALL) uses separable pseudopotential (Hamann or Troullier) goes beyond minimal ${\mathrm{sp}}^{2}$ basis set of Sankey-Niklewski method, allowing double numerical sets with addition polarization orbitals d set. A major improvement includes use more...
We report a first-principles study of ${({\text{LaAlO}}_{3})}_{m}/{({\text{SrTiO}}_{3})}_{n}$ heterostructures using density-functional theory at the $\text{LDA}+U$ level. Our results support original explanation Ohtomo and Hwang [Nature (London) 427, 423 (2004)] that charge $n$-type interface may be due to electrostatic doping. The internal electric field in ${\text{LaAlO}}_{3}$ layer is calculated $0.24\text{ }\text{V}/\text{\AA{}}$. Though it not sufficient cause dielectric breakdown wide...
The electronic structure of oxygen vacancies in bulk perovskite oxides SrTiO${}_{3}$ and LaAlO${}_{3}$ is studied using the Heyd, Scuseria, Ernzerhof (HSE) hybrid density functional. In vacancy defect introduces a localized state comprised $3{d}_{{z}^{2}}$ $4{p}_{z}$ orbitals adjacent Ti atoms. This results bound 0.7 eV below conduction band edge. For LaAlO${}_{3}$, creates deep 2.19 La 5$d$ Al 3$p$ states. We compute formation energies neutral V${}^{0}$ to be 6.0 8.3 eV, respectively.
Various mechanisms for the Fermi level pinning of p-gate metals on HfO2 are analyzed in detail. It is found that energies below Si valence band, can oxidize by creating positively charged O vacancies. The band bending due to this vacancy concentration account observed p HfO2.
TiO2 is being widely explored as an active resistive switching (RS) material for random access memory. We report a detailed analysis of the RS characteristics single-crystal anatase-TiO2 thin films epitaxially grown on silicon by atomic layer deposition. demonstrate that although valence change mechanism responsible observed RS, show electrical are very different from usual behaviors polycrystalline or amorphous and instead similar to those found in electrochemical metallization In addition,...
In the present study, we combine theoretical and experimental approaches in order to gain insight into electronic properties of both high-temperature, rutile (metallic) low-temperature, body-centered tetragonal (insulating) phase niobium dioxide (NbO2) as well optical low-temperature phase. Theoretical calculations performed at level local density approximation, Hubbard U correction, hybrid functional are complemented with spectroscopic ellipsometry (SE) epitaxial films grown by molecular...
Oxygen vacancies are an important type of defect in transition metal oxides. In ${\mathrm{SrTiO}}_{3}$ they believed to be the main donors otherwise intrinsic crystal. At same time, a relatively deep gap state associated with vacancy is widely reported. To explain this inconsistency we investigate effect electron correlation oxygen (OV) ${\mathrm{SrTiO}}_{3}$. When taking into account, find that OV-induced localized level can at most trap one electron, while second occupies conduction band....
Significant progress has been made in integrating novel materials into silicon photonic structures order to extend the functionality of circuits. One these promising optical is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show noticable reduction effect BTO thin films deposited on substrates compared bulk crystals. Here, we report strong dependence their microstructure, and...
Abstract Crystallization of hafnia and zirconia their alloys with silica lanthana was studied in bulk thin film samples by thermal analysis, X‐ray diffraction electron microscopy. temperatures increase more than 300 °C surface/interface area the amorphous phase. dopant content exceed 900 for 50 mol% SiO 2 LaO 1.5 . Energies tetragonal HfO ZrO interfaces were derived from crystallization enthalpies silicates as 0.25 ± 0.08 0.13 0.07 J/m , respectively. The pathways powders films can be...
We have performed a first-principles investigation of the microscopic properties random crystalline Si-C alloys. An ab initio tight-binding molecular-dynamics method is used to determine atomic structure For small moderate concentrations C in Si, we find that electronic shows decrease band gap from pure Si. This result unexpected since both ordered SiC and carbon (diamond) much larger gaps than Plane-wave calculations were also done on structures further check this effeats ordering....
Most semiconductor materials such as Si, Ge, and GaAs are subject to oxidation when exposed oxidants. This results in difficulties the heterointegration of epitaxial oxides on these semiconductors. Even though certain may be thermodynamically stable placed contact with semiconductors, direct epitaxy encounters kinetic due loss caused by formation an amorphous oxide at interface. In this article, we address some important issues heteroepitaxy semiconductors show a stepped growth method that...
We predict theoretically the wetting conditions for layer-by-layer growth of thin ${\mathrm{SrTiO}}_{3}$ (STO) films on Si. The result is in agreement with our recent experiments. state art band offset calculations identify two different possibilities alignment at Si-STO interface. A very small conduction predicted structure without chemically induced localization interface, and a 0.9 eV localized interface states.
We use a combination of density functional theory and calorimetric measurements to investigate the monoclinic tetragonal transition in hafnia zirconia. measure enthalpies be $8.4\ifmmode\pm\else\textpm\fi{}0.7\text{ }\text{kJ}/\text{mol}$ and, as previously reported, $5.272\ifmmode\pm\else\textpm\fi{}0.544\text{ Calculated values are 10.21 7.50 kJ/mol for zirconia, respectively. formulate theoretical model phase consistent with martnesitic character transformations. The barriers 20.3 16.3...
While the physics of Schottky barrier is relatively well understood, much less known about band alignment at insulator/insulator interface. As a model problem we study theoretically technologically important $\mathrm{Si}{\mathrm{O}}_{2}∕\mathrm{Hf}{\mathrm{O}}_{2}$ interface using density functional theory. We report several different atomic level models this along with their energies and electronic properties. find that valence offset increases near linearly interfacial oxygen coordination,...
Ferromagnet/ferroelectric/normal-metal superlattices are proposed to realize the large room-temperature magnetoelectric effect. Spin-dependent electron screening is fundamental mechanism at microscopic level. We also predict an electric control of magnetization in this structure. The naturally broken inversion symmetry our tricomponent structure introduces a coupling energy $P{M}^{2}$. Such effect general ferromagnet/ferroelectric heterostructures, independent particular chemical or physical...
The biomineral hydroxyapatite Ca${}_{10}$(PO${}_{4}$)${}_{6}$(OH)${}_{2}$ is the main mineral constituent of mammal bone. Hydroxyapatite crystallizes in hexagonal and monoclinic phases, difference between them being orientation hydroxyl groups. Using density functional theory, we study energetics along with several hypothetical crystal structures hydroxyapatite. phase has lowest energy, only 22 meV/cell higher energy. We identify a structural transition path from to phase, activation energy...
Atomic layer deposition (ALD) is a proven technique for the conformal of oxide thin films with nanoscale thickness control. Most successful industrial applications have been binary oxides, such as Al2O3 and HfO2. However, there has much effort to deposit ternary perovskites (ABO3), desirable properties advanced film applications. Distinct challenges are presented by multi-component oxides using ALD. This review intended highlight research many groups that deposited perovskite ALD methods....
Using spin density functional theory with the Hubbard correction, we investigate magnetic structure of strained LaCoO${}_{3}$. We show that beyond biaxial tensile strain 2.5$%$, local moments originating from high state Co${}^{3+}$ emerge in a low matrix. In contrast, find compressive is not able to stabilize due geometric constraints. LaCoO${}_{3}$ accommodates via spin-state disproportionation, resulting an unusual sublattice structure. tensile-strained LaCoO${}_{3}$, first...