Korean researchers build semiconductor, insulator and electrode into single atomic layer

- IBS and Postech team develops selective atomic substitution technology at 0.7-nanometer scale

- Transistor achieved without stacking process; findings published in Science

From left: Cho Hyeon-je, a student researcher at the IBS Center for Van der Waals Quantum Solids and a doctoral candidate in the Department of Materials Science and Engineering at Postech; Cho Moon-ho, director of the center; and Min Seok-young, a postdoctoral researcher. [Institute for Basic Science]

Korean researchers have developed a technology that selectively replaces atoms within a semiconductor to embed a semiconductor layer, insulating film and electrode junction all within a single thin film — without stacking multiple materials. The advance opens a new path toward ultrafine, ultralow-power semiconductors.

The Ministry of Science and ICT and the Institute for Basic Science (IBS) announced Friday that a research team led by Cho Moon-ho, director of the IBS Center for Van der Waals Quantum Solids and a distinguished professor at Postech, had developed a "modular transistor fabrication technology." The technology selectively substitutes atoms within a two-dimensional semiconductor to create different electrical properties at targeted positions and layers.

The findings were published Friday in the journal Science.

As AI technology spreads, the ability to increase semiconductor integration density while reducing power consumption has become increasingly important. Two-dimensional semiconductors — just a few atomic layers thick — are drawing attention as a next-generation material capable of overcoming the miniaturization limits of conventional silicon semiconductors.

Two-dimensional semiconductors, however, have posed persistent challenges: other materials do not adhere well to their surfaces, making it difficult to form a uniform insulating layer, and directly attaching metal electrodes produces high contact resistance.

Rather than stacking different materials in the conventional way, the research team found a breakthrough by changing the atoms inside the semiconductor itself.

The material the team used was tungsten diselenide (WSe₂), a structure in which selenium atomic layers sandwich a tungsten atomic layer above and below. Replacing the selenium atoms with different atoms alters the material's electrical properties.

By substituting the selenium atoms with oxygen, sulfur and tellurium respectively, the team produced tungsten oxide (WOₓ), an insulator; tungsten disulfide (WS₂), an n-type semiconductor; and tungsten ditelluride (WTe₂), a semimetal with high electrical conductivity.

By controlling reaction temperature and gas pressure, the team succeeded in converting material at the atomic-layer level — at a thickness of about 0.7 nanometers (one-billionth of a meter). This allowed them to realize a transistor within a single thin film that incorporates a semiconductor, an insulating layer and an electrode junction.

With the semimetal junction layer applied, the energy barrier that charge carriers must overcome during transport fell to 35.5 millielectronvolts (meV) — roughly one-third the level seen when a metal electrode is connected directly.

The on/off current ratio also exceeded 10 million to one, meaning current can be precisely controlled with only small changes in voltage.

A conceptual diagram of modular two-dimensional transistor fabrication using selective atomic-layer substitution. [Institute for Basic Science]

The equivalent oxide thickness (EOT) of the insulating layer also came in at under 1 nanometer, meeting the performance targets for ultrafine devices set out in the International Roadmap for Devices and Systems.

The most significant aspect of the research is that the key components of a transistor were realized through atomic substitution within a single thin film, rather than by fabricating and stacking separate materials. The work presents a new approach that can both reduce the complexity of semiconductor manufacturing processes and improve device performance.

However, follow-up research will be needed to ensure uniform performance across large-area wafer-scale processes before the technology can be applied industrially.

The team plans to extend the atomic substitution technology to a wider range of two-dimensional semiconductor materials and to pursue large-area wafer processing and three-dimensional stacked integrated circuit development.

"This research is significant in that it bridges the techniques of fundamental materials science — atomic-level manipulation of matter — with modern semiconductor technology, opening a breakthrough for a qualitative leap in future semiconductor development," Cho said. "It will be expandable not only to ultralow-power, ultrafine semiconductors but also to next-generation stacked semiconductor device technologies."

nbgkoo@heraldcorp.com