8,561 research outputs found
Band alignment and p-type doping of ZnSnN2
No full textPublisher's PDFComposed of earth-abundant elements, ZnSnN2 is a promising semiconductor for photovoltaic and
photoelectrochemical applications. However, basic properties such as the precise value of the band gap and
the band alignment to other semiconductors are still unresolved. For instance, reported values for the band gap
vary from 1.4 to 2.0 eV. In addition, doping in ZnSnN2 remains largely unexplored. Using density functional
theory with the Heyd-Scuseria-Ernzerhof hybrid functional, we investigate the electronic structure of ZnSnN2,
its band alignment to GaN and ZnO, and the possibility of p-type doping. We find that the position of the
valence-band maximum of ZnSnN2 is 0.39 eV higher than that in GaN, yet the conduction-band minimum is
close to that in ZnO, which suggests that achieving p-type conductivity is likely as in GaN, yet it may be difficult
to control unintentional n-type conductivity as in ZnO. Among possible p-type dopants, we explore Li, Na, and
K substituting on the Zn site. We show that while LiZn is a shallow acceptor, NaZn and KZn are deep acceptors,
which we trace back to large local relaxations around the Na and K impurities due to the atomic size mismatches.University of Delaware. Department of Materials Science and Engineering
Small polarons and point defects in barium cerate
No full textPublisher's PDFBarium cerate (BaCeO3) is a well-known ionic conductor of both hydrogen and oxygen. In applications, it
is frequently doped (for instance with Y) to increase stability and promote diffusion. However, the effects of
doping and native defects are not fully understood. Computational studies have been stymied by the nature
of the conduction band, which is made up of cerium 4f states. These states present a challenge to ab initio
techniques based on density functional theory within the standard approximations for exchange and correlation.
Using a hybrid functional, we investigate the effects of hydrogen impurities and native defects on the electrical
and optical properties of BaCeO3. We discuss the tendency of excess electrons or holes to localize in the form
of small polarons. We also explore the interactions of polarons with hydrogen impurities and oxygen vacancies,
and their impact on luminescence properties.University of Delaware. Department of Materials Science and Engineering
Correct Implementation of Polarization Constants in Wurtzite Materials and Impact on III-Nitrides
No full textPublisher's PDFAccurate values for polarization discontinuities between pyroelectric materials are critical for understanding and designing the electronic properties of heterostructures. For wurtzite materials, the zincblende structure has been used in the literature as a reference to determine the effective spontaneous polarization constants. We show that, because the zincblende structure has a nonzero formal polarization, this method results in a spurious contribution to the spontaneous polarization differences between materials. In addition, we address the correct choice of “improper” versus “proper” piezoelectric constants. For the technologically important III-nitride materials GaN, AlN, and InN, we determine polarization discontinuities using a consistent reference based on the layered hexagonal structure and the correct choice of piezoelectric constants, and discuss the results in light of available experimental data.University of Delaware. Department of Materials Science and Engineering
Chapter 14: MD Anderson Publications and Publication Ethics
No full textDr. Goepfert has served on a number of editorial boards and is keenly interested in the educational dissemination of information critical to cancer research. In this section he talks about some of MD Anderson’s publications and also addresses some controversies with publication. He first raises the ethical issue of how authorship is assigned to a manuscript going out for publication. Today there are guidelines for assigning authorship, but twenty years ago, he explains, some department chairs at MD Anderson reviewed all manuscripts going for publication and insisted on being listed as first author of an article, whether they made any contribution to the research or not. Dr. Goepfert contrasts his own practice of putting his name on a paper only if he has contributed. Dr. Goepfert then shifts subjects and describes several MD Anderson educational publications, beginning with Cancer Bulletin, distributed free to all physicians across Texas.https://openworks.mdanderson.org/mchv_interviewchapters/2010/thumbnail.jp
Defects as qubits in 3C- and 4H-SiC
No full textPublisher's PDFWe employ hybrid density functional calculations to search for defects in different polytypes of SiC that
may serve as qubits for quantum computing. We explore the divacancy in 4H- and 3C-SiC, consisting of a
carbon vacancy adjacent to a silicon vacancy, and the nitrogen-vacancy (NV) center in 3C-SiC, in which the
substitutional NC sits next to a Si vacancy (NC-VSi). The calculated excitation and emission energies of the
divacancy in 4H-SiC are in excellent agreement with experimental data, and aid in identifying the four unique
configurations of the divacancy with the four distinct zero-phonon lines observed experimentally. For 3C-SiC,
we identify the paramagnetic defect that was recently shown to maintain a coherent quantum state up to room
temperature as the spin-1 neutral divacancy. Finally, we show that the (NC-VSi)− center in 3C-SiC is highly
promising for quantum information science, and we provide guidance for identifying this defect.University of Delaware. Department of Materials Science and Engineering
Promise - Spring 2020
No full textRogers Award honors MD Anderson nursing assistant MD Anderson awards highest nursing honor Low-grade serous ovarian cancer survivor establishes research nonprofit Celebrity Chef Cooking Demo makes young cancer patients sous-chefs for a day Bob’s Encore: hope in the fight against pancreatic cancer Board of Visitors welcomes seven new members Board of Visitors awards highest distinction to longtime member A Conversation with a Living Legend raises 2 million for cancer research, education and prevention Get to know Advance Team’s Laura Nelson Cookbook author leaves her mark on gastric cancer researchhttps://openworks.mdanderson.org/promise/1001/thumbnail.jp
Chapter 09: Strengthening Biomedical Editing Nationwide and Within MD Anderson
No full textIn this Chapter, first briefly notes his involvement with the Southwest Chapter of the American Medical Writer’s Association and the Council of Biology Editors (with a 22-year membership). He then explains that he had his biggest impact while he served on the Board of Editors in the Life Sciences and in the late 80s worked on the Editorial Certification Examination Development Committee. He describes the examination he helped create to certify competence for editors of biomedical articles and explains the significance of certification. He notes that the Department of Scientific Publications at MD Anderson uses its own battery of tests to evaluate editors’ abilities for abstract reasoning, grammar, and other skills and talents.
Next, Mr. Pagel talks about his Department’s blog, “The Write Stuff,” and two significant projects: his role on the Historical Resources Center Steering Committee, and the development of panel discussions for the Department of Scientific Publications. To begin the discussion of the Steering Committee, he notes that Scientific Publications wrote The First Twenty Years, the first history of MD Anderson. Because of this association with the institution’s history, Mr. Pagel was asked to be part of the Steering Committee when the Historical Resources Center was formed and set as its first goal the publication of an updated institutional history. Mr. Pagel wanted the perspective to be broader than the first book, situating MD Anderson and cancer research in a larger context of other cancer institutions and the history of cancer research. Though not alone in holding this view, he says he had something to do with articulating it for the benefit of the Steering Committee. He describes how James Olsen was selected to be the author and notes other Steering Committee activities.https://openworks.mdanderson.org/mchv_interviewchapters/2275/thumbnail.jp
(InxGa1−x)2O3 alloys for transparent electronics
No full textPublisher's PDF(InxGa1−x )2O3 alloys show promise as transparent conducting oxides. Using hybrid density functional
calculations, band gaps, formation enthalpies, and structural parameters are determined for monoclinic and
bixbyite crystal structures. In the monoclinic phase the band gap exhibits a linear dependence on alloy
concentration, whereas in the bixbyite phase a large band-gap bowing occurs. The calculated formation enthalpies
showthat the monoclinic structure is favorable for In compositions up to 50% and bixbyite for larger compositions.
This is caused by In strongly preferring sixfold oxygen coordination. The formation enthalpy of the 50:50
monoclinic alloy is much lower than the formation enthalpy of the 50:50 bixbyite alloy and also lower than most
monoclinic alloys with lower In concentration; these trends are explained in terms of local strain. Consequences
for experiment and applications are discussed.University of Delaware. Department of Materials Science and Engineering
Electronic properties of corundum-like Ir2O3 and Ir2O3-Ga2O3 alloys
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Shoaib Khalid, Anderson Janotti; Electronic properties of corundum-like Ir2O3 and Ir2O3-Ga2O3 alloys. Appl. Phys. Lett. 11 November 2024; 125 (20): 202102. https://doi.org/10.1063/5.0232445 and may be found at https://doi.org/10.1063/5.0232445.
© 2024 Author(s). Published under an exclusive license by AIP Publishing.
This article will be embargoed until 11/11/2025.In the hexagonal, corundum-like structure, -Ga2O3 has a bandgap of 5.1 eV, which, combined with its relatively small electron effective mass, high Baliga's figure of merit, and high breakdown field, makes it a promising candidate for power electronics. Ga2O3 is easy to dope n-type, but impossible to dope p-type, impeding the realization of some electronic device designs. Developing a lattice-matched p-type material that forms a high-quality heterojunction with n-type Ga2O3 would open new opportunities in electronics and perhaps optoelectronic devices. In this work, we studied Ir2O3 as a candidate for that purpose. Using hybrid density functional theory calculations we predict the electronic band structure of -Ir2O3 and compare that to -Ga2O3, and study the stability and electronic properties of -(IrxGa1−x)2O3 alloys. We discuss the band offset between the two materials and compare it with recently available experimental data. We find that the Ir d bands that compose the top of the valence band in -Ir2O3 are much higher in energy than O p bands in -Ga2O3, possibly enabling effective p-type doping. Our results provide an insight into using the Ir2O3 or Ir2O3-Ga2O3 alloys as p-type material lattice-matched to -Ga2O3 for the realization of p–n heterojunctions.This work was supported by the Laboratory Directed Research and Development (LDRD) Program (Project No. 800025) at Princeton Plasma Physics Laboratory under U.S. Department of Energy Prime Contract No. DE-AC02-09CH11466. A.J. was supported by the NSF through the UD-CHARM University of Delaware Materials Research Science and Engineering Center (MRSEC) Grant No. DMR-2011824. The calculations were carried out at the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at the Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231 using NERSC award BES-ERCAP27253, the Stellar Cluster at Princeton University, and the DARWIN computing system at the University of Delaware, using the NSF Grant No. 1919839
First-principles study of surface charging in LaAlO3/SrTiO3 heterostructures
No full textPublsiher's PDFThe two-dimensional electron gas (2DEG) observed at the interface between LaAlO3 (LAO) and SrTiO3 (STO)
is known to be very sensitive to the proximity of the LaAlO3 surface and the conditions to which the surface is
exposed. We use first-principles calculations to study surface reconstructions on LAO films, taking into account
that the LAO surface can be charged. The results for the charged surfaces and for the coupling between the
surface and the 2DEG enable us to account not only for the behavior of the 2DEG as a function of thickness of the
LAO layer, but simultaneously determine the stable terminations and reconstructions on the LAO surface under
a variety of conditions. Our studies of charged surfaces are based on an extension of the methodology of A. Y.
Lozovoi et al. [J. Chem. Phys. 115, 1661 (2001)]. From the calculated electronic structure of the unreconstructed
(but relaxed) AlO2 and LaO surface terminations of LAO, we find surface states having excess holes (AlO2
termination) or excess electrons (LaO termination). This result is central to understanding the mechanism of
2DEG formation, and is consistent with a 2DEG of density 3.3 × 1014 cm−2 being intrinsic to the LaO-TiO2
interface in the LAO/STO system. We explore the effects of the Al-adatom, O-vacancy, and H-adatom surface
reconstructions on the 2DEG density, and find that the stability of different reconstructions is tied to the thickness
of the LAO layer as well as the surface exposure conditions. We find that including the effects of charging of
the surface significantly stabilizes the AlO2 termination versus the LaO termination. Overall, our methodology
has the advantage of decoupling first-principles calculations for the interface from those for the charged surface,
and constitutes a general approach that can be applied to the commonly occurring problem of charge exchange
between the surface and the interface of a thin film with a substrate, or between the surface and defects/impurities
in the bulk of a material.
DOI: 10.1103/PhysRevB.University of Delaware. Department of Materials Science and Engineering
- …
