Scientists control where 2D semiconductor crystals begin to grow, addressing key challenge in stacking AI chips

by The Korea Advanced Institute of Science and Technology (KAIST)

edited by Sadie Harley, reviewed by Robert Egan

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Add to Preferred Sources Schematic of the principle by which oxygen acts as an etching flux that suppresses crystal formation, so that a 2D semiconductor begins to grow at only one designated point. Credit: The Korea Advanced Institute of Science and Technology (KAIST) Two-dimensional (2D) semiconductors, only a few atomic layers thick, are promising materials for making AI chips faster and more energy efficient by stacking additional semiconductor layers on top of existing computing circuits. However, when crystals form at multiple random locations during growth, it is difficult to produce high-quality semiconductors at the desired positions.

A joint KAIST research team has developed a technology that sets in advance where a crystal begins to grow and allows only one crystal to grow at that position. By controlling the starting point of semiconductor growth, the work addresses a key challenge in realizing next-generation stacked semiconductors.

A research team led by Professor Kibum Kang from the Department of Materials Science and Engineering, in collaboration with UNIST, Hanyang University and TDS Innovation (co-CEOs Kang and Sanghyun Mo), has developed a new growth technique that precisely controls the location of nucleation, the stage at which 2D semiconductor crystals first form, using chemical species released from an oxide barrier.

The work is published in the journal Nature.

When AI generates responses or processes large amounts of data, time and power are consumed not only by computation but also by moving data within the chip.

Stacking the devices used for computation and data storage vertically, so that they are placed close together, shortens the distance that data must travel and can reduce processing delays and power consumption. This requires a technology that forms high-quality semiconductors directly at the required positions on top of circuits that have already been fabricated.

Deposited semiconductors, in which devices are made by forming a thin film of semiconductor material directly on the required surface, are a promising technology for building stacked chips. 2D semiconductors are particularly well suited for stacking thin device layers because they retain the electrical properties of a semiconductor while being only a few atomic layers thick.

The challenge is that, as a thin semiconductor film grows, the positions where crystals begin to form are inherently random. A crystal is a structure in which the atoms that make up the semiconductor are arranged in a regular, repeating pattern. When crystals grow separately from several locations and meet, grain boundaries form between them. These boundaries hinder the movement of electrons and can degrade the quality of the semiconductor.

Area-selective growth techniques, which define in advance the regions where a semiconductor will grow, already exist. However, it has been difficult to control exactly where crystals first form within those regions and how many of them form.

The research team achieved deterministic nucleation, in which nucleation that previously occurred at random takes place one at a time at defined positions. In addition to defining the region where the semiconductor will grow, the team also determined the point within that region where growth begins.

The researchers named the technique etching-flux-mediated single-centered nucleation (EF-SCN). The key element is oxygen released from an oxide barrier, such as hafnium oxide (HfO₂), that surrounds the growth region. This oxygen acts as an etching flux that suppresses the formation of crystal nuclei of molybdenum disulfide (MoS₂), a representative 2D semiconductor.

Etching refers to chemically removing material, and flux refers to the flow of a specific chemical species that is transported and supplied in a way that affects nearby chemical reactions.

The suppressing effect is strong at the edges near the oxide barrier and becomes weaker toward the center, which is farthest from the barrier. Using this difference, the team caused a single crystal to begin growing at only one point in the center.

While the crystal that started at the center continued to grow, the formation of new crystals around it was also suppressed, so that the single crystal could grow larger.

In experiments, the team grew one MoS₂ single crystal at a designated central position in more than 99% of 400 different patterns. A single crystal has one continuous atomic arrangement, and because it reduces the boundaries that form where multiple crystals meet, it is advantageous for producing high-quality semiconductors.

Using MoS₂–MoSe₂ lateral heterostructures grown with this method, the team also deposited a thin film of ruthenium (Ru) metal selectively on the molybdenum diselenide (MoSe₂) regions only. The researchers further analyzed the principle behind this position control through growth experiments and simulations.

The significance of this work is that it turns the starting point of semiconductor thin-film growth, which had been determined at random, into a process parameter that can be designed. Instead of fabricating 2D semiconductors elsewhere and then transferring them, this approach could lead to a manufacturing technology that grows high-quality semiconductors directly at the required positions on a chip.

Deposited semiconductors are expected to be adopted in the 2030s to improve the performance and lower the power consumption of AI chips. If applied to stacked AI chips, the technology could reduce the time and energy spent on moving data, which would shorten the time users wait for AI responses and reduce the power demands of data centers.

"In thin-film growth, where a crystal forms is inherently a matter of probability, and the key significance of this study is that it allows that starting point to be determined at a desired position," said Kang.

Kang added that the technology will serve as the basis for stacked-channel processes, in which semiconductor devices are stacked vertically, by growing high-quality 2D semiconductors directly where they are needed.

"In 2D semiconductors, the position where growth begins can change in response to even small chemical changes in the surroundings," said Dr. Jeongwon Park, a co-first author. Park explained that the significance of the study lies in using this property to control where the semiconductor begins to grow.

Jeongwon Park et al., Spatially deterministic nucleation of 2D semiconductors by etching flux, Nature (2026). DOI: 10.1038/s41586-026-11095-1 Journal information: Nature

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