Overcoming stacking constraints in hexagonal boron nitride by way of metal-organic chemical vapor deposition

Researchers from Pohang College of Science and Know-how (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-about unattainable.

This achievement, completed by way of 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 gadgets.

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

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

hBN has lengthy been thought to be a key insulating materials for 2D digital, photonic, and quantum functions. Usually, hBN adopts an AA’ stacking configuration, by 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-about unstable resulting from sturdy interlayer electrostatic repulsion.

By means of detailed investigation, the analysis crew 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 progress 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 vital function of digital doping by way of 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 sometimes 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 by way of 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 technology (SHG)—an indicator of non-centrosymmetric crystal constructions—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 gadgets working within the DUV spectrum.

“Reaching wafer-scale management of stacking order is a crucial milestone for scalable, high-performance 2D digital and photonic methods,” mentioned 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.”