From computers the size of an office floor to two-dimensional semiconductors invisible to the human eye, electronics are shrinking while gaining power — but can the source materials keep up? Silicon dioxide, the insulator typically used as an interface between semiconductors, works well down to a size about 50,000 times smaller than a human hair. Beyond that, it leaks, resulting in more power use and faulty electronics. To improve the device performance at even smaller scales, 2D semiconductors may offer a solution. However, there is still the challenge of developing a high-quality interface between 2D semiconductors and the electrical insulator. Researchers based in China and Singapore have successfully demonstrated the benefits of a new strategy that can be applied to improve the interface properties.
They published their results on Jan. 5 in the Nano Research.
“Two-dimensional semiconducting materials are appealing for nanoelectronic applications,” said paper author Shijie Wang, senior scientists at the Institute of Materials Research and Engineering in the Agency for Science, Technology and Research in Singapore. “Among them, monolayer transition metal disulfides (TMDs), such as monolayer molybdenum disulfide, has attracted tremendous interest as promising channel materials for electronic or optoelectronic devices due to their stability, direct band gaps, tunable electronic and optical properties and many other excellent physical properties.”
The comparatively low ability of silicon dioxide to store electric energy at the nanoscale, however, is a barrier to realizing monolayer TMDs in practical applications, Wang said. Materials with a higher energy capacity, called high-k dielectrics, are available, but traditionally do no interface well with monolayer TMDs because their charge states can deteriorate electronic properties and the integration can damage the 2D semiconductors.
“In this study, we proposed selective hydrogenation as an ideal strategy because hydrogen atoms are prone to adsorption on the surface of high-k dielectrics but inert to the basal planes of 2D TMDs,” said paper author Ming Yang, assistant professor of applied physics, The Hong Kong Polytechnic University. “Another benefit of this hydrogenation process is that it can also passivate the intrinsic defects in 2D semiconductors, such as sulfur vacancies in molybdenum disulfide, which can further improve the device performance.”
The researchers studied the interface between molybdenum disulfide, the TMD 2D semiconductor, and silicon nitride, the high-k dielectric. Hydrogenation — the process by using hydrogen treatment— occurs spontaneously at this interface, adhering to the high-k dielectric but leaving the TMD intact. The hydrogenation can passivate the dangling molecular bonds on high-k dielectrics without damaging the 2D semiconductor. According to Yang, this results in improved interface properties that are better supported by the electronic structure, band offsets and reduced interface charge states.
“We revealed that the hydrogenated interface is stable at high temperatures, which is compatible with the current semiconductor fabrication process,” Yang said. “Given the similar surface chemistry among TMD semiconductors, this hydrogenation process can be extended to the interfaces of many high-k dielectrics and a broad range of TMDs or other 2D materials that are inert to hydrogen adsorption, enabling us to boost the development of 2D semiconductor-based nanoelectric devices.”
The researchers also tested the strategy with hafnium oxide, another high-k dielectric, and found similar results.
“Our results demonstrate a simple yet viable way to improve the integration of high-k dielectrics on a broad range of 2D TMD semiconductors, shedding light on practical electronic and optoelectronic applications,” Wang said.
Other contributors include Yulin Yang, Hongyi Zhang and Wenzhang Zhu, Fujian Provincial Key Laboratory of Optoelectronic Technology and Devices, School of Optoelectronic and Communication Engineering, Xiamen University of Technology, China; Tong Yang, The Hong Kong Polytechnic University’s Department of Applied Physics; Tingting Song, China West Normal University’s College of Physics and Space Science; and Jun Zhou, Jianwei Chai, and LaiMun Wong, Institute of Materials Research and Engineering in the Agency for Science, Technology and Research in Singapore.
The Hong Kong Polytechnic University, the National University of Singapore’s Centre for Advanced 2D Materials and Graphene Research and the National Supercomputing Centre of Singapore supported this research.
About Nano Research
Nano Research is a peer-reviewed, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society. It offers readers an attractive mix of authoritative and comprehensive reviews and original cutting-edge research papers. After more than 10 years of development, it has become one of the most influential academic journals in the nano field. Rapid review to ensure quick publication is a key feature of Nano Research. In 2020 InCites Journal Citation Reports, Nano Research has an Impact Factor of 8.897 (8.696, 5 years), the total cites reached 23150, and the number of highly cited papers reached 129, ranked among the top 2.5% of over 9000 academic journals, ranking first in China's international academic journals.
Established in 1980, belonging to Tsinghua University, Tsinghua University Press (TUP) is a leading comprehensive higher education and professional publisher in China. Committed to building a top-level global cultural brand, after 41 years of development, TUP has established an outstanding managerial system and enterprise structure, and delivered multimedia and multi-dimensional publications covering books, audio, video, electronic products, journals and digital publications. In addition, TUP actively carries out its strategic transformation from educational publishing to content development and service for teaching & learning and was named First-class National Publisher for achieving remarkable results.
Selective hydrogenation improves interface properties of high-k dielectrics on 2D semiconductors
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