Doctoral Dissertations

Author

Rabi Khanal

Keywords and Phrases

Ab Initio Moleculardynamics; Amorphous Oxides; Density Functional Theory; Electronic Structure; Semiconductors; Transparent Conductors

Abstract

"Amorphous transparent conducting and semiconducting oxides possess properties superior or comparable to their crystalline counterparts. The structure-property relationship in amorphous oxides is not nearly as well understood as in the case of the crystalline transparent conducting oxides. We have employedab initio molecular dynamics and a liquid quench approach to simulate amorphous oxide structures and performed density functional-based calculations to study the electronic properties of several amorphous conducting and semiconducting oxides with various cation compositions.

The effect of amorphization in oxides was investigated by taking indium oxide as a progenitor of the system. From the thorough study it was confirmed that the distribution and connectivity of naturally coordinated indium polyhedra (InO6) depend on the cooling rates used in the quenching process. Also, it was shown experimentally that the transport properties depend strongly on the deposition temperature, in particular, the carrier Hall mobility is enhanced at the onset of the amorphous region to become similar to the mobility in crystalline In2O3. Our results have shown that the corresponding amorphous structure exhibits a long chain of the InO6 connected primarily via corner sharing, thus, highlighting the importance of the medium/long-range structural characteristics.

To understand the effect of chemical composition on the structure and properties of amorphous oxides, In-X-O with X=Sn, Zn, Ga, Cd, Ge, Sc, Y, or La, were studied. The results reveal that the short-range structure of the metal-O polyhedra is preserved in the amorphous oxides; therefore, the extended nature of the conduction band, the key feature of transparent conducting oxide, is maintained. Unlike the case of crystalline transparent oxides, additional cation in amorphous oxides does not act as a dopant. Instead, the presence of X affects the number of naturally coordinated In atoms as well as the oxygen sharing between metal-oxygen polyhedra which ultimately affects the transport properties"--Abstract, page iv.

Advisor(s)

Medvedeva, Julia E.

Committee Member(s)

Wilemski, Gerald
Parris, Paul Ernest, 1954-
Brow, Richard K.
Grayson, Matthew

Department(s)

Physics

Degree Name

Ph. D. in Physics

Sponsor(s)

National Science Foundation (U.S.)
United States. Department of Energy

Publisher

Missouri University of Science and Technology

Publication Date

Fall 2016

Journal article titles appearing in thesis/dissertation

  • The structure and properties of amorphous indium oxide
  • Long-range structural correlations in amorphous ternary In-based oxides
  • Cation size effects on the electronic and structural properties of solution-processed In-X-O thin films
  • Composition-dependent structural and transport properties of amorphous transparent conducting oxides

Pagination

xvii, 162 pages

Note about bibliography

Includes bibliographic references.

Rights

© Rabi Khanal

Document Type

Dissertation - Open Access

File Type

text

Language

English

Library of Congress Subject Headings

Molecular dynamics
Thin films
Density functionals
Electronic structure
Semiconductors

Thesis Number

T 11032

Electronic OCLC #

974710315

Comments

For this research, R.P.H.C., R.K., and J.E.M. were supported by the MRSEC program of the National Science Foundation at Northwestern University under grant no. DMR- 1121262. D.B.B. was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under the Award Number DE-FG02-06ER46320. This work made use of the J.B. Cohen X-ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1121262) at the Materials Research Center of Northwestern University; the Optical Microscopy and Metallography Facility MRSEC program of the National Science Foundation. X-ray absorption measurements were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by E.I. DuPont de Nemours & Co., The Dow Chemical Company, and Northwestern University. Use of the APS, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. Computational resources were provided by the NSF supported XSEDE program, grant TG-DMR080007. Electron microscopy was supported by the National Center for Research Resources (5 G12RR013646-12) and Department of Defense #64756-RT-REP. D.A., A.P., and M.J.-Y. also thank NSF PREM Grant # DMR 0934218.

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