Growth Condition-Oriented Defect Engineering for Changes in Au⁻ZnO Contact Behavior from Schottky to Ohmic and Vice Versa

• Published in: Nanomaterials (Basel, Switzerland) Switzerland), 2018-11, Vol.8 (12), p.980
• Main Authors: Rana, Abu Ul Hassan Sarwar, Kim, Hyun-Seok
• Format: Article
• Language: English
• Subjects: Carrier density; Carrier transport; Communication; crystal defects; Defects; Engineering; Growth conditions; Hydrogen; metal-semiconductor contact; Methods; microwave; Microwaves; Morphology; nanorod; Nanorods; Nitrates; Organic chemistry; Oxygen plasma; oxygen plasma treatment; Photovoltaic cells; Polyethylene terephthalate; R&D; Research & development; Seeds; Semiconductors; Sensors; Thin films; Zinc oxide; Zinc oxides; ZnO
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano8120980

ZnO has the built-in characteristics of both ionic and covalent compound semiconductors, which makes the metal⁻ZnO carrier transport mechanism quite intricate. The growth mechanism-centric change in ZnO defect density and carrier concentration also makes the contact formation and behavior unpredictable. This study investigates the uncertainty in Au⁻ZnO contact behavior for application-oriented research and the development on ZnO nanostructures. Herein, we explain the phenomenon for how Au⁻ZnO contact could be rectifying or non-rectifying. Growth method-dependent defect engineering was exploited to explain the change in Schottky barrier heights at the Au⁻ZnO interface, and the change in device characteristics from Schottky to Ohmic and vice versa. The ZnO nanorods were fabricated via aqueous chemical growth (ACG) and microwave-assisted growth (MAG) methods. For further investigations, one ACG sample was doped with Ga, and another was subjected to oxygen plasma treatment (OPT). The ACG and Ga-doped ACG samples showed a quasi-Ohmic and Ohmic behavior, respectively, because of a high surface and subsurface level donor defect-centric Schottky barrier pinning at the Au⁻ZnO interface. However, the ACG-OPT and MAG samples showed a more pronounced Schottky contact because of the presence of low defect-centric carrier concentration via MAG, and the removal of the surface accumulation layer via the OPT process.