Selective Doping Without Damaging 2D Semiconductors... Current Increased by Up to 260 Times [Reading Science]

KAIST Blocks Plasma Damage with 2 nm Dual Protective Layer
Selective Doping Only Where Needed... Reduces Contact Resistance to One-Thirty-Second

A technology has been developed that enables selective doping of two-dimensional semiconductors at the atomic layer level, without damaging their structure. By overcoming the challenge of atomic layer damage during the doping process—a longstanding issue with next-generation semiconductor materials—this technique reduced contact resistance to one thirty-second of its original value and increased the current flow at low voltage by up to 260 times.

On September 7, the National Research Foundation of Korea (NRF) announced that a joint research team led by Professors Choi Sungyul, Kim Yonghun, and Kang Gibum of Korea Advanced Institute of Science and Technology (KAIST) has developed a technique that uses an ultra-thin dual protective layer to protect the crystal structure of molybdenum disulfide (MoS₂) two-dimensional semiconductors, while enabling high-concentration electron doping only in desired areas.

Principle of doping two-dimensional semiconductors using an ultrathin protective layer. The dual protective layer blocks the physical impact of plasma while allowing only NHx active species necessary for doping to pass through, thereby increasing the electron concentration without damaging the MoS₂ crystal structure. Provided by the research team

Two-dimensional semiconductors are extremely thin—at the atomic layer level—while maintaining their electrical characteristics, making them a promising candidate to surpass the miniaturization limits of traditional silicon-based semiconductors. However, "doping" presents a problem. In order to adjust the electrical properties of semiconductors and lower resistance, it is necessary to introduce specific substances to change the electron concentration. In conventional plasma-based processes, high-energy particles can collide with the thin atomic layers, damaging their crystal structure.

The research team addressed this issue by stacking two different ultra-thin layers of about 2 nm in thickness to create a dual protective layer. This protective layer serves as a kind of "chemical filter"—it blocks the physical impact of high-energy particles from plasma while allowing the NHx active species required for doping to pass through.

Blocking Plasma Impact, Letting Only Doping Substances Pass

By applying this method, the electron concentration can be increased while preserving the crystal structure of two-dimensional semiconductors. Using this approach, the team succeeded in reducing contact resistance between the semiconductor and the electrode to one thirty-second of the conventional level.

In particular, they also implemented "area-selective resistance control," which allows doping to be applied solely to certain regions—specifically along the electron conduction path where resistance must be reduced—rather than over the entire semiconductor. As a result, the current under very low voltage conditions was increased by up to 260 times.

The unique aspect of this technique is that it enables modification of the electrical characteristics only at targeted locations, without damaging the atomic layers. In the future, it is expected to be applicable to ultra-miniature low-power logic devices, monolithic three-dimensional semiconductors in which semiconductor layers are continuously stacked onto a single wafer, and two-dimensional material-based CMOS.

However, additional validation is needed before the technique can be applied to actual semiconductor manufacturing processes. Professor Choi Sungyul of KAIST stated, "To apply this method to practical semiconductor manufacturing processes, further verification regarding doping uniformity, process time reduction, and doping area control in ultra-miniaturized devices is required."

This research was supported by the Ministry of Science and ICT and the National Research Foundation of Korea through the Nano-Material Technology Development Program and the Mid-Career Research Program. The results were published on August 1 in the international journal Advanced Materials.

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