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dc.contributor.advisorO'Hayre, Ryan P.
dc.contributor.advisorGinley, D. S. (David S.)
dc.contributor.authorKe, Yi
dc.contributor.committeememberOhno, Timothy R.
dc.contributor.committeememberGorman, Brian P.
dc.contributor.committeememberBerry, Joseph
dc.contributor.committeememberToberer, Eric
dc.date.accessioned2007-01-03T06:01:11Z
dc.date.available2007-01-03T06:01:11Z
dc.date.issued2014
dc.date.submitted2014
dc.description2014 Spring.
dc.descriptionIncludes illustrations (some color).
dc.descriptionIncludes bibliographical references (pages 90-96).
dc.description.abstractAlloying MgO into ZnO substantially increases the band-gap energy but reduces the conductivity and makes it harder to be doped with donors. While the former makes it attractive as energy-level-tunable transparent conducting contacts, the latter limits its applications. By combining high quality material synthesis, characterization and theory, we attribute the major limitation on the electrical conductivity of epitaxial Ga-doped Zn0.7Mg0.3O to intrinsic acceptors, such as zinc vacancies, which both trap carriers and increase the ionized impurity scattering (IIS). In addition, it shows that zinc vacancies can form defect complexes with Ga substituted on a Zn site (GaZn) during annealing, and this can increase the mobility by reducing the number of IIS centers. This work establishes that enhancing defect pairing is an effective strategy to increase mobility in semiconductors where IIS limits the transport. Epitaxial Zn0.7Mg0.3O:Ga (1%) thin films were deposited on c-sapphire substrates by pulsed laser deposition. Temperature-dependent Hall effect measurements results indicate that the samples are degenerately n-doped and the mobility is limited by IIS. However, the doping efficiency of Ga is only around 40%. TEM imaging and composition analysis indicate that neither extended defects nor impurities are present at sufficient levels to account for the low ionization efficiency. Thus, we consider intrinsic defects. The detailed analysis of electrical properties suggests that ionized electron killers are present. First-principles calculations of formation enthalpies find that zinc vacancies (VZn) have the lowest formation enthalpy among intrinsic acceptors. Considering a simple model with just four kinds of defects (isolated GaZn, isolated VZn, GaZn-VZn pairs and 2GaZn-VZn clusters), we can derive their concentrations from four independent equations with measured n, µ and Ga concentration as inputs. Analysis performed on samples with different annealing times shows that as-deposited films have more isolated VZn than predicted for thermodynamic equilibrium. Upon annealing, the samples approach equilibrium as indicated by a decrease in the concentration of isolated VZn and a corresponding increase in the concentration of GaZn-VZn pairs and 2GaZn-VZn clusters. This clustering of oppositely charged defects reduces the number of ionized impurities consistent with an increase in mobility from 11.5 cm2/Vs to 17.4 cm2/Vs upon annealing.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.identifierT 7399
dc.identifier.urihttp://hdl.handle.net/11124/171
dc.languageEnglish
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2014 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectdefect-pairing
dc.subjectZnMgO
dc.subjecttransparent conducting oxides
dc.subjectdoping
dc.subjectconductivity
dc.subjectband-gap engineering
dc.subject.lcshSemiconductors
dc.subject.lcshZinc oxide
dc.subject.lcshSemiconductor doping
dc.subject.lcshThin films -- Electric properties
dc.subject.lcshThin films -- Optical properties
dc.subject.lcshTransparent semiconductors
dc.subject.lcshElectric conductivity
dc.titleTowards improved understanding and conductivity in band-gap-tunable zinc magnesium oxide
dc.typeText
thesis.degree.disciplineMetallurgical and Materials Engineering
thesis.degree.grantorColorado School of Mines
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy (Ph.D.)


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