Acceptor Conductivity In Bulk ZnO (0001) Crystals

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Title: Acceptor Conductivity In Bulk ZnO (0001) Crystals
Author: Adekore, Bunmi Tolu
Advisors: Robert F. Davis, Committee Chair
Salah Bedair, Committee Member
Douglas Barlage, Committee Member
Robert Kolbas, Committee Member
Klaus Bachmann, Committee Member
Abstract: ZnO is a promising wide bandgap semiconductor. Its renowned and prominent properties as its bandgap of 3.37eV at 4.2K; its very high excitonic binding energy, 60meV; its high melting temperature, 2248K constitute the basis for the recently renewed and sustained scientific interests in the material. In addition to the foregoing, the availability of bulk substrates of industrially relevant sizes provides important opportunities such as homoepitaxial deposition of the material which is a technological asset in the production of efficient optoelectronic and electronic devices. The nemesis of wide bandgap materials cannot be more exemplified than in ZnO. The notorious limitation of asymmetric doping and the haunting plague of electrically active point defects dim the bright future of the material. In this case, the search for reliable and consistent acceptor conductivity in bulk substrates has been hitherto, unsuccessful. In the dissertation that now follows, our efforts have been concerted in the search for a reliable acceptor. We have carefully investigated the science of point defects in the material, especially those responsible for the high donor conductivity. We also investigated and herein report variety of techniques of introducing acceptors into the material. We employ the most relevant and informative characterization techniques in verifying both the intended conductivity and the response of intrinsic crystals to variation in temperature and strain. And finally we explain deviations, where they exist, from ideal acceptor characteristics. Our work on reliable acceptor has been articulated in four papers. The first establishing capacitance based methods of monitoring electrically active donor defects. The second investigates the nature of anion acceptors on the oxygen sublattice. A study similar to the preceding study was conducted for cation acceptors on the zinc sublattice and reported in the third paper. Finally, an analysis of the response of the crystal to hydrostatic strain and its recovery when such strain enforces a collapse of its crystallinity is reported in the fourth paper. For the sake of brevity and the need to be concise, our supplementary investigations on extrinsic donor conductivity is deferred to other journal publications.
Date: 2005-05-04
Degree: PhD
Discipline: Materials Science and Engineering

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