Overcoming stacking constraints in hexagonal boron nitride through metal-organic chemical vapor deposition

Researchers from Pohang College of Science and Expertise (POSTECH) and the College of Montpellier have efficiently synthesized wafer-scale hexagonal boron nitride (hBN) exhibiting an AA-stacking configuration, a crystal construction beforehand thought of unattainable.

This achievement, completed through metal-organic chemical vapor deposition (MOCVD) on a gallium nitride (GaN) substrate, introduces a novel route for exact stacking management in van der Waals supplies, impacting potential functions in quantum photonics, deep-ultraviolet (DUV) optoelectronics, and next-generation digital units.

The research, led by Professors Jong Kyu Kim and Si-Younger Choi (POSTECH) and Guillaume Cassabois (College of Montpellier), gives key insights into the components influencing unconventional stacking configurations.

Printed in Nature Supplies, the findings problem earlier assumptions about stacking constraints in hBN, demonstrating that step-edge-guided development and cost incorporation are important in stabilizing the thermodynamically unfavorable AA stacking configuration.

hBN has lengthy been considered a key insulating materials for 2D digital, photonic, and quantum functions. Sometimes, hBN adopts an AA’ stacking configuration, through which boron and nitrogen atoms alternate vertically between layers. In distinction, the AA stacking configuration―the place an identical atoms align vertically―has historically been thought of unstable as a result of robust interlayer electrostatic repulsion.

By way of detailed investigation, the analysis workforce found that step-edges on vicinal GaN substrates function nucleation websites, selling the unidirectional alignment of hBN layers and minimizing rotational dysfunction. This step-edge guided development mechanism enabled the formation of high-quality, wafer-scale AA-stacked hBN movies, guaranteeing each structural uniformity and crystallinity required for sensible digital and photonic functions.

Moreover, the research highlights the crucial function of digital doping via carbon incorporation in the course of the MOCVD course of. The presence of carbon introduces extra cost carriers, altering interlayer interactions and successfully mitigating the repulsive forces usually related to AA stacking. Collectively, this charge-mediated stabilization and step-edge alignment represent a beforehand unexplored mechanism for engineering tailor-made stacking sequences in van der Waals supplies.

“Our analysis demonstrates that stacking configurations in van der Waals supplies should not purely ruled by thermodynamic issues, however can as a substitute be stabilized via substrate traits and cost incorporation,” remarked Professor Jong Kyu Kim, who led the research. “This perception considerably expands the potential for custom-made 2D materials architectures with distinct digital and optical properties.”

Optical characterization of the synthesized AA-stacked hBN revealed enhanced second-harmonic era (SHG)—a trademark of non-centrosymmetric crystal buildings—indicating promising functions in nonlinear optics. Moreover, the fabric exhibited sharp band-edge emission within the DUV area, suggesting its potential for high-efficiency optoelectronic units working within the DUV spectrum.

“Attaining wafer-scale management of stacking order is a crucial milestone for scalable, high-performance 2D digital and photonic programs,” stated Seokho Moon, a postdoctoral researcher in Professor Jong Kyu Kim’s lab and the lead creator of the research.

“This work highlights the flexibility of MOCVD as a platform for exactly engineered van der Waals supplies.”