Patterning Smaller Junctions for Ultrathin Devices

Newswise — The Science

Making faster, more powerful electronics requires smaller but still uniform connections, or junctions, between different materials. For the first time, researchers created extremely small, 5-nanometer-wide junctions, which were made in a specific pattern using two different planar, or flat, semiconductors. The simple process to create these two-dimensional junctions involved selective exposure of the semiconductor to laser-vaporized material and could be extended to other systems.

The Impact

Controllably creating patterned semiconductor junctions in thin planar materials could enable ultrathin microelectronics for numerous applications such as in smartphones, next-generation solar cells, and lighting.

Summary

Junctions of two-dimensional (2D) semiconductors could enable next-generation photovoltaics, lighting, and electronics. For example, current electronics rely on 10-nanometer-wide junctions between different semiconductors in three-dimensional (3D) crystals. Controllable synthetic methods are needed to create narrow junctions between different 2D materials. Now, researchers at Oak Ridge National Laboratory have developed a process for creating these junctions between different 2D semiconductors in arbitrary patterns using standard electron beam lithography techniques. Single layers of molybdenum diselenide (MoSe₂) crystals less than a nanometer thick were first patterned with a silicon oxide mask and then exposed to laser-vaporized sulfur. The sulfur atoms replaced the selenium atoms in the exposed regions, selectively converting MoSe2 to molybdenum disulfide (MoS₂). Chemical mapping with Raman spectroscopy confirmed the chemical conversion was uniform. Atomic-resolution electron microscopy revealed that the junctions between the different semiconductors were only 5 nanometers wide. Patterning such sharp junctions could facilitate a range of ultrathin devices from flexible consumer electronics to more efficient solar cells.

Funding

This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (synthesis science) and the Center for Nanophase Materials Sciences (optical characterization and lithography), a DOE Office of Science User Facility, and the National Secretariat of Higher Education, Science, Technology and Innovation of Ecuador.

Publications

M. Mahjouri-Samani, M. Lin, K. Wang, A. Lupini, J. Lee, L. Basile, A. Boulesbaa, C. Rouleau, A. Puretzky, I. Ivanov, K. Xiao, M. Yoon, and D. Geohegan, “Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors.” Nature Communications 6, 7749 (2015). [DOI: 10.1038/ncomms8749].