KAIST

< The research team. From left: Gayeon Lee, Ph.D. student; Mingyu Jang, student in the integrated M.S.–Ph.D. program; Changhwan Kim, student in the integrated M.S.–Ph.D. program; Professor Joonki Suh; Namwook Hur, student in the integrated M.S.–Ph.D. program; and Dr. Wenxuan Zhu, postdoctoral researcher. >

Building next-generation semiconductors and low-power electronic devices requires precisely stacking materials with different functions. In this process, it is essential to preserve each material's intrinsic properties, as well as the interface where the two materials meet, without damage. Layered van der Waals materials, including transition metal dichalcogenides (TMDs), have attracted considerable attention as next-generation semiconductor platforms because their layers interact through weak forces, enabling different materials to be stacked while maintaining atomically clean interfaces.

KAIST (President Choongsik Bae) announced on the 27th of July that a research team led by Professor Joonki Suh from the Department of Chemical and Biomolecular Engineering, in collaboration with Professor Bonggeun Shong's team at Hanyang University and Professor Yimo Han's team at Rice University in the United States, has developed a new semiconductor manufacturing technique based on atomic layer deposition (ALD). ALD is a thin-film deposition process in which semiconductor precursor are supplied sequentially, enabling uniform thin films to be deposited with atomic-level control over their thickness.

The research team focused on van der Waals materials. These two-dimensional semiconductor materials consist of multiple atomic layers held together by weak interlayer forces, allowing them to be peeled apart into sheets as thin as paper. Because different materials can be freely stacked, van der Waals materials are attracting attention as key building blocks for next-generation AI chips and ultra-low-power semiconductor devices.

However, their chemically stable surfaces make it difficult to grow new semiconductor layers in a uniformly aligned orientation. This challenge becomes even greater at lower temperatures, where atoms tend to nucleate and grow in random directions, making it difficult to produce high-performance semiconductor films.

The research team developed a new method that allows tellurium (Te)-containing precursors—molecular building blocks used to fabricate semiconductors—to move freely across the surface, find the most energetically stable positions, and form a thin film.

< Figure 1. Diffusion-steered epitaxial atomic layer deposition of tellurium and structural character of tellurium grown on WSe₂. The figure illustrates how precursors first adsorb weakly onto the van der Waals surface, diffuse across it, and initiate tellurium crystal growth at energetically stable positions. Electron microscopy and optical and structural analyses confirmed that the tellurium grew along a consistent crystallographic orientation, forming a clean interface between the two materials while maintaining extremely low interfacial distortion. The results also demonstrate that, unlike conventional high-temperature growth processes, this technique enables epitaxial growth at a low temperature of 150°C. >

Tellurium is attracting attention as a key material for next-generation semiconductors and optoelectronic devices, including photodetectors and light-emitting diodes (LEDs), because it combines highly direction-dependent electrical conductivity with excellent light-controlling properties.

Using this approach, the research team succeeded in achieving epitaxial growth of tellurium uniformly in a single direction on van der Waals materials— next-generation two-dimensional semiconductor materials composed of multiple atomically thin layers stacked like sheets of paper— at a low temperature of 150°C using ALD. In epitaxial growth, a new semiconductor film grows in an ordered manner following the atomic arrangement of the underlying crystal, enabling the precise fabrication of high-quality semiconductor films. This process is comparable to stacking bricks neatly in the same direction rather than placing them randomly, which can improve electrical transport and enhance semiconductor performance.

The researchers also confirmed that the technology could be applied to a range of van der Waals materials, including tungsten diselenide (WSe2), molybdenum disulfide (MoSS), rhenium diselenide (ReSe2), and mica. This demonstrates that the method is not limited to a single material but can be broadly used with various next-generation semiconductor materials.

The team further used the resulting semiconductor films to fabricate transistors, key semiconductor devices that control the flow of electrical current, as well as optoelectronic devices that detect or emit light. This demonstrated that the new manufacturing technology is not confined to laboratory-scale material growth but can also be applied to the fabrication of functional semiconductor devices.

< Figure 2. Conceptual illustration of tellurium thin-film growth using diffusion-steered epitaxial atomic layer deposition. The image depicts the process in which two types of precursors are supplied onto a van der Waals surface, diffuse across the surface, and form a tellurium thin film aligned in a consistent crystallographic direction at energetically stable positions. (AI-generated image) >

"This study is the first to demonstrate that high-quality semiconductor films can be grown on van der Waals materials at low temperature without damaging the underlying materials," said Professor Suh. "We expect this technology to serve as a key manufacturing platform for integrating a wide range of next-generation semiconductors on a single chip," he added.

The study, with Changhwan Kim, a doctoral student, as first author and Professor Suh as corresponding author, was published in the journal Science Advances on July 24.

Paper title: Van der Waals template-encoded soft epitaxy of tellurium enabled by atomic layer deposition

DOI: 10.1126/sciadv.aef1430

Author information: Changhwan Kim (Korea Advanced Institute of Science and Technology / Ulsan National Institute of Science and Technology, first author) and Joonki Suh (Korea Advanced Institute of Science and Technology, corresponding author)

This research was supported by the National Research Foundation of Korea, under the Ministry of Science and ICT.