Ultra-large single-crystal WS2 monolayer
New technique opens a possibility to replace silicon with 2D materials in semiconducting technology

Date:
November 15, 2021
Source:
Institute for Basic Science
Summary:
A new technique opens a possibility to replace silicon with 2D
materials in semiconducting technology.



FULL STORY ==========================================================================
As silicon based semiconducting technology is approaching the limit of
its performance, new materials that may replace or partially replace
silicon in technology is highly desired. Recently, the emergence of
graphene and other two-dimensional (2D) materials offers a new platform
for building next generation semiconducting technology. Among them,
transition metal dichalcogenides (TMDs), such as MoS2, WS2, MoSe2, WSe2,
as most appealing 2D semiconductors.


==========================================================================
A prerequisite of building ultra-large-scale high-performance
semiconducting circuits is that the base materials must be a
single-crystal of wafer-scale, just like the silicon wafer used
today. Although great efforts have been dedicated to the growth of
wafer-scale single-crystals of TMDs, the success was very limited
until now.

Distinguished Professor Feng Ding and his research team from the Center
for Multidimensional CarbonMaterials (CMCM), within the Institute for
Basic Science (IBS) at UNIST, in cooperation with researcher at Peking University (PKU), Beijing Institute of Technology, and Fudan University, reported the direct growth of 2-inch single-crystal WS2 monolayer films
very recently. Besides the WS2, the research team also demonstrated the
growth of single-crystal MoS2, WSe2, and MoSe2 in wafer scale as well.

The key technology of epitaxially grown a large sing-crystal is to
ensure that all small single-crystal grown on a substrate are uniformly aligned. Because TMDs has non-centrosymmetric structure or the mirror
image of a TMD with respect to an edge of it has opposite alignment,
we must break such a symmetry by carefully design the substrate. Based
on theoretical calculations, the authors proposed a mechanisms of "dual-coupling-guided epitaxy growth" for experimental design. The WS2-sapphireplane interaction as the first driving force, leading to
two preferred antiparallel orientations of the WS2islands.

The coupling between WS2 and sapphire step-edge is the second
driving force and it will break the degeneracy of the two antiparallel orientations. Then all the TMD single crystals grown on a substrate with
step edges are all unidirectional aligned and finally, the coalescence
of these small single-crystals leads to a large single-crystal of the
same size of the substrate.

"This new dual-coupling epitaxy growth mechanism is new for controllable materials growth. In principle, it allows us realize to grow all 2D
materials into large-area single crystals if proper substrate was
found." Says Dr. Ting Cheng, the co-first author of the study. "We
have considered how to choose proper substrates theoretically. First,
the substrate should have a low symmetry and, secondly, more step edges
are preferred." emphasizes Professor Feng Ding, the corresponding author
of the study.

"This is a major step forward in the area of 2D materials based device. As
the successful growth of wafer-scale single-crystal 2D TMDs on insulators beyond graphene and hBN on transition metal substrates, our study provide
the required keystone of 2D semiconductors in high-end applications of electronic and optical devices," explains professor Feng Ding.

========================================================================== Story Source: Materials provided by Institute_for_Basic_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jinhuan Wang, Xiaozhi Xu, Ting Cheng, Lehua Gu, Ruixi Qiao,
Zhihua Liang,
Dongdong Ding, Hao Hong, Peiming Zheng, Zhibin Zhang, Zhihong
Zhang, Shuai Zhang, Guoliang Cui, Chao Chang, Chen Huang, Jiajie
Qi, Jing Liang, Can Liu, Yonggang Zuo, Guodong Xue, Xinjie Fang,
Jinpeng Tian, Muhong Wu, Yi Guo, Zhixin Yao, Qingze Jiao, Lei
Liu, Peng Gao, Qunyang Li, Rong Yang, Guangyu Zhang, Zhilie Tang,
Dapeng Yu, Enge Wang, Jianming Lu, Yun Zhao, Shiwei Wu, Feng Ding,
Kaihui Liu. Dual-coupling-guided epitaxial growth of wafer-scale
single-crystal WS2 monolayer on vicinal a-plane sapphire. Nature
Nanotechnology, 2021; DOI: 10.1038/s41565-021-01004-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211115123536.htm

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