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This review presents recent research advances in measuring native point defects in ZnO nanostructures, establishing how these defects a ect nanoscale electronic properties, and developing new techniques to manipulate these defects to control nano- and micro- wire electronic properties.From spatially-resolved cathodoluminescence spectroscopy, we now know that electrically-active native point defects are present inside, as well as at the surfaces of, ZnO and other semiconductor nanostructures. These defects within nanowires and at their metal interfaces can dominate electrical contact properties, yet they are sensitive to manipulation by chemical interactions, energy beams, as well as applied electrical fields. Non-uniform defect distributions are common among semiconductors, and their e ects are magnified in semiconductor nanostructures so that their electronic e ects are significant. The ability to measure native point defects directly on a nanoscale and manipulate their spatial distributions by multiple techniques presents exciting possibilities for future ZnO nanoscale electronics.
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Defect Manipulation to Control ZnO Micro-/Nanowire-Metal Contacts
Surface states that induce depletion regions are commonly believed to control the transport of charged carriers through semiconductor nanowires. However, direct, localized optical, and electrical measurements of ZnO nanowires show that native point defects inside the nanowire bulk and created at metal−semiconductor interfaces are electrically active and play a dominant role electronically, altering the semiconductor doping, the carrier density along the wire length, and the injection of charge into the wire. We used depth-resolved cathodoluminescence spectroscopy to measure the densities of multiple point defects inside ZnO nanowires, substitutional Cu on Zn sites, zinc vacancy, and oxygen vacancy defects, showing that their densities varied strongly both radially and lengthwise for tapered wires. These defect profiles and their variation with wire diameter produce trap-assisted tunneling and acceptor trapping of free carriers, the balance of which determines the low contact resistivity (2.6 × 10−3 Ω·cm−2) ohmic, Schottky (Φ ≥ 0.35 eV) or blocking nature of Pt contacts to a single nano/microwire. We show how these defects can now be manipulated by ion beam methods and nanowire design, opening new avenues to control nanowire charge injection and transport.
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- Award ID(s):
- 1800130
- PAR ID:
- 10165321
- Date Published:
- Journal Name:
- Nano letters
- Volume:
- 18
- ISSN:
- 1530-6984
- Page Range / eLocation ID:
- 6974-6980
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/DOI: 10.1021/acs.nanolett.8b02892
