Rana Abu Ul Hassan Sarwar, Kim Hyun-Seok
Division of Electronics and Electrical Engineering, Dongguk University-Seoul, Seoul 04620, Korea.
Nanomaterials (Basel). 2018 Nov 27;8(12):980. 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.
氧化锌具有离子化合物半导体和共价化合物半导体的固有特性,这使得金属-氧化锌载流子传输机制相当复杂。以生长机制为中心的氧化锌缺陷密度和载流子浓度变化也使得接触形成和行为难以预测。本研究针对面向应用的氧化锌纳米结构研究与开发,探究金-氧化锌接触行为的不确定性。在此,我们解释了金-氧化锌接触如何能够形成整流或非整流的现象。利用与生长方法相关的缺陷工程来解释金-氧化锌界面处肖特基势垒高度的变化,以及器件特性从肖特基型到欧姆型以及反之的变化。氧化锌纳米棒通过水热化学生长(ACG)和微波辅助生长(MAG)方法制备。为了进一步研究,一个水热化学生长样品掺杂了镓,另一个进行了氧等离子体处理(OPT)。由于在金-氧化锌界面处存在以高表面和次表面能级施主缺陷为中心的肖特基势垒钉扎,水热化学生长和镓掺杂的水热化学生长样品分别表现出准欧姆和欧姆行为。然而,由于通过微波辅助生长存在以低缺陷为中心的载流子浓度,以及通过氧等离子体处理过程去除了表面积累层,水热化学生长-氧等离子体处理和微波辅助生长样品表现出更明显的肖特基接触。