An intermediate catalytic crystal helps semiconductors grow epitaxially on 2D substrates

Creating a low-defect interface between materials with different chemical bonding is a key challenge in the development of functional metamaterials. Specifically, lining up the atomic structure of a 3D material as it grows onto a 2D substrate can generate advantageous electronic properties. Periwal et al. demonstrated a method to grow 3D semiconductors epitaxially onto 2D substrates.

“What we found was a way to encourage materials that do not naturally line up well – such as germanium on graphene – to do so,” said author Frances Ross. “The encouragement takes place by using an intermediate material that satisfies several conditions: it lines up on the substrate very well itself, it acts as a catalyst, helping to grow our target material, and the target material grows with a strong alignment to the catalyst.”

This chain of materials creates what the authors call “transfer of epitaxy,” whereby the alignment between the target material and the catalyst and alignment between the catalyst and the 2D material work together to help the target material align with the substrate’s crystal structure.

The group grew gold nanocrystals onto a graphene substrate, then used gold as a catalyst to grow a semiconductor, germanium. The gold nanocrystals grew with good alignment on the graphene, and the germanium nanocrystals inherited their orientation, making the germanium well-aligned with the graphene.

“This intermediate catalytic material can be thought of as a bridge that is aligned with both the substrate and the growing material,” Ross said.

The strategy is useful for nanoelectronic and photonic applications and can be extended to more complex materials and structures. One challenge that remains is determining how to adapt the approach for larger-scale growth.

Source: “Catalytically mediated epitaxy of 3D semiconductors on van der Waals substrates,” by Priyanka Periwal, Joachim Dahl Thomsen, Kate Reidy, Georgios Varnavides, Dmitri N. Zakharov, Lynne Gignac, Mark C. Reuter, Timothy J. Booth, Stephan Hofmann, and Frances M. Ross, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/5.0006300 .