Engineering Tailored Configurations in van der Waals Materials

Researchers at Pohang University of Science and Technology (POSTECH) and the University of Montpellier have successfully achieved the wafer-scale synthesis of hexagonal boron nitride (hBN) with an AA-stacking configuration. This crystal structure was previously considered unfeasible.

This method utilizes metal-organic chemical vapor deposition (MOCVD) on a gallium nitride (GaN) substrate. It offers a new approach for precise stacking control in van der Waals materials, enabling advancements in quantum photonics, deep-ultraviolet (DUV) optoelectronics, and next-generation electronic devices.

Led by Professors Jong Kyu Kim and Si-Young Choi (POSTECH) and Guillaume Cassabois (University of Montpellier), the study provides insights into the factors affecting unconventional stacking configurations. The findings challenge prior assumptions about stacking constraints in hBN, showing that step-edge guided growth and charge incorporation are essential for stabilizing the thermodynamically unfavorable AA-stacking configuration.

hBN is considered an essential insulating material for 2D electronic, photonic, and quantum applications. It typically adopts an AA' stacking configuration, where boron and nitrogen atoms alternate vertically between layers. The AA-stacking configuration, where identical atoms align vertically, has been regarded as unstable due to strong interlayer electrostatic repulsion.

Through detailed analysis, the researchers found that step-edges on vicinal GaN substrates act as nucleation points, facilitating aligned growth of hBN layers while reducing rotational misalignment. This step-edge guided growth process enabled the production of wafer-scale AA-stacked hBN films with high structural uniformity and crystallinity, making them suitable for electronic and photonic applications.

The research highlights the significant role of electronic doping through carbon incorporation during the MOCVD process. Structural and spectroscopic analyses at POSTECH and the Pohang Accelerator Laboratory (4D and 10D beamlines) confirmed the presence of carbon, which generates excess charge carriers, modifies interlayer interactions, and reduces the repulsive forces typically associated with AA stacking.

The combination of charge-mediated stabilization and step-edge alignment presents a new approach for designing customized stacking sequences in van der Waals materials, an area previously not explored.

Our research demonstrates that stacking configurations in van der Waals materials are not purely governed by thermodynamic considerations, but can instead be stabilized through substrate characteristics and charge incorporation. This insight significantly expands the potential for customized 2D material architectures with distinct electronic and optical properties.

Jong Kyu Kim, Professor, Pohang University of Science and Technology

Optical analysis of the synthesized AA-stacked hBN revealed increased second-harmonic generation (SHG), a characteristic feature of non-centrosymmetric crystal structures, demonstrating its potential for nonlinear optics. Additionally, the material showed distinct band-edge emission in the DUV region, suggesting its suitability for high-performance optoelectronic devices in this spectrum.

Achieving wafer-scale control of stacking order is an important milestone for scalable, high-performance 2D electronic and photonic systems. This work highlights the versatility of MOCVD as a platform for precisely engineered van der Waals materials.

Seokho Moon, Postdoctoral Researcher and Study Lead Author, Pohang University of Science and Technology

The research was funded by the Global Ph.D. Fellowship Program and the Basic Science Research Capacity Enhancement Program (Materials Imaging & Analysis Research Center) of the Ministry of Education, as well as the Mid-Career Researcher Program and the Nano and Materials Technology Development Program of the Ministry of Science and ICT. Additional support was provided by the Electronic Components Industry Technology Development Program of the Ministry of Trade, Industry & Energy, and Samsung Electronics.

Journal Reference:

Moon, S., et al. (2025). Wafer-scale AA-stacked hexagonal boron nitride grown on a GaN substrate. Nature Materials. doi.org/10.1038/s41563-025-02173-2.