Research Bits: October 3

2D semiconductors: indium selenide and molybdenum ditelluride.


Growing indium selenide at scale

Researchers from the University of Pennsylvania, Brookhaven National Laboratory, and the Air Force Research Laboratory grew the 2D semiconductor indium selenide (InSe) on a full-size, industrial-scale wafer. It can also be deposited at temperatures low enough to integrate with a silicon chip.

The team noted that producing large enough films of InSe has proven tricky because the chemistry of indium and selenium tends to combine in a few different molecular proportions, taking on chemical structures with varying ratios of each element and thus compromising its purity.

“For the purposes of an advanced computing technology, the chemical structure of 2D InSe needs to be exactly 50:50 between the two elements. The resulting material needs a uniform chemical structure over a large area to work,” said Seunguk Song, postdoctoral fellow in the Department of Electrical and Systems Engineering at the University of Pennsylvania.

To create this, they used vertical metal-organic chemical vapor deposition to send the indium in a continuous stream while introducing the selenium in pulses. “By pulsing, you give the indium and selenium time to combine. In the moments between pulses, you deprive the environment of selenium, which prevents the ratio from getting too high. The benefit of the pulse is the pause. That’s how we get a uniform 50:50 ratio across our entire full-size wafer,” says Song.

The method also enabled the team to control and align the direction of crystals in the material, enhancing the quality of the semiconductor further by providing a seamless environment for electron transport.

Seunguk Song, Sungho Jeon, Mahfujur Rahaman, Jason Lynch, Dongjoon Rhee, Pawan Kumar, Srikrishna Chakravarthi, Gwangwoo Kim, Xingyu Du, Eric W. Blanton, Kim Kisslinger, Michael Snure, Nicholas R. Glavin, Eric A. Stach, Roy H. Olsson, Deep Jariwala. Wafer-scale growth of two-dimensional, phase-pure InSe. Matter, 2023;

Fabricating molybdenum ditelluride p-type transistor arrays

Researchers from the Ulsan National Institute of Science and Technology (UNIST), University of Pennsylvania, and Sogang University are developing high-performance p-type semiconductor devices utilizing molybdenum ditelluride (MoTe2).

They used chemical vapor deposition to synthesize large-area 4-inch MoTe2 wafers with high purity by depositing a three-dimensional metal onto a two-dimensional semi-metal, effectively modulating barrier layers that prevent charge carriers from entering. This approach leverages three-dimensional metals acting as protective films for two-dimensional metals, resulting in improved yields and enabling transistor array device implementation.

“The significance of our research extends beyond MoTe2,” said Sora Jang of UNIST. “The device manufacturing method developed can be applied to various two-dimensional materials, opening doors for further advancements in this field.”

Song, S., Yoon, A., Jang, S. et al. Fabrication of p-type 2D single-crystalline transistor arrays with Fermi-level-tuned van der Waals semimetal electrodes. Nat Commun 14, 4747 (2023).

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