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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.85

Epitaxial Growth of Bendable Cubic NiO and In2O3 Thin Films on Synthetic Mica for p- and n-type Wide-Bandgap Semiconductor Oxides Yuta Arata1, Hiroyuki Nishinaka2, Kazuki Shimazoe1, and Masahiro Yoshimoto2 1

Department of Electronics, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan.

2

Faculty of Electrical Engineering and Electronics, Kyoto Institute of Technology, Matsugasaki, Sakyoku, Kyoto, 606-8585, Japan.

Abstract

Bendable p-type NiO and n-type In2O3 thin films were epitaxially grown on synthetic mica using mist chemical vapor deposition. It was found that at a growth temperature of 400 °C, epitaxially grown cubic (111) NiO thin films developed twin rotational domains, and the epitaxial relationship between each domain and the substrate was (111) NiO [1-10] or [10-1] || (001) synthetic mica [100]. In the visible light region, the epitaxial NiO thin films showed high transparencies, and their cut-offs appeared in the UV region. Additionally, at a growth temperature of 500 °C, cubic (111) In2O3 thin films with and without Sn doping were epitaxially grown on synthetic mica. As a result of the plasma oscillation of free carriers, Sndoped In2O3 thin films exhibited reflection characteristics in the infrared region, while maintaining their visible light transmission characteristics. Furthermore, compared with nondoped In2O3, Sn doping decreased the sheet resistance by two digits.

INTRODUCTION As the world moves towards the Trillion Sensors Universe, the demand for flexible electronic devices is increasing significantly. Given that organic materials can be easily formed on flexible substrates using ink-jet printing or spin coating, several studies dedicated to investigating the application of organic-material-based flexible devices, such as organic light-emitting diodes (OLEDs) and ferroelectric devices [1,2], have been conducted. However, the heat resistance of these organic materials is generally low, and

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under moist atmospheric conditions and exposure to UV radiation sources, including sunlight, they do not show long-term stability. Thus, it is necessary to establish a technology that is stable, and can be used in the long-term. For inorganic materials with excellent stability, their single or uniformly oriented crystals exhibit better characteristics than their polycrystalline or amorphous. However, the plastic substrates that are typically used in flexible electronic devices are generally amorphous, and are unable to epitaxially grow single or uniformly oriented crystals. Additionally, these inorganic materials often require high temperatures for crystal growth, and the plastic substrates have a low resistance to heat, and hence, cannot be used for crystal growth at high temperatures.