The complexity and potential of ultrathin films of group III nitrides

The project GRIFONE was among the 13 research projects selected for funding by the FLAG-ERA Joint Transnational Call 2015 in synergy with the Graphene Flagship. It involved Associate Member Linköping University in Sweden, Graphene Flagship Partners the Hungarian Academy of Sciences, the Institute for Technical Physics and Materials Science (MFA) in Hungary, and the National Research Council - Institute for Microelectronics and Microsystems (CNR-IMM) in Italy. GRIFONE aims to grow atomically thin layers of group III nitrides, such as aluminum nitride (AlN).

An important building block for modern optoelectronics, AlN has a large band gap and naturally crystalizes in a 3D structure, the so-called wurtzite structure. Obtaining ultrathin AlN films is more challenging, but also opens new opportunities for the development of nanoscale optoelectronics and room-temperature spintronics. These are likely to require AlN integration with other layered materials, particularly graphene.

GRIFONE researchers studied models of few-layer "graphitic-like" AlN integrated with graphene in different stacking configurations. They investigated its structure, interaction energy and electronic properties. Published in Nanotechnology, these findings have implications for understanding how few-layer AlN changes from "graphitic-like" to wurtzite structure, and they also explain the reactivity and adhesion properties of these heterostructures.

The researchers then produced few-layer "graphitic-like" AlN sandwiched between a graphene and a silicon carbide substrate. They used the metal organic chemical vapor deposition (MOCVD), a scalable and industrially compatible deposition process. The analysis revealed that the distance between AlN layers closely matches their theoretical modeling, and is much shorter than the interlayer distance of bilayer hexagonal boron nitride – a widely-studied layered nitride – or bilayer graphene. This indicates a strong interaction between the AlN layers, which influences the electronic properties, such as the bandgap, of this innovative material.

With large scale simulations, the researchers deepened their understanding of the nanoscale dynamics taking place during the AlN synthesis, and went beyond the resolution of MOCVD experiments. They modelled the interactions of graphene with AlN precursor molecules trimethylaluminum, (CH₃)₃Al, and ammonia: in a mechanism essential for the formation of ultrathin AlN, the strongly-bonded (CH₃)₃Al dissociates and individual Al atoms are adsorbed on the graphene layer.

By implementing a related MOCVD deposition protocol, the team reported the formation of another ultrathin group III nitride: indium nitride (InN). Its bandgap of 2 eV paves the way for pragmatic applications.

"Starting from the initial material identification, we successfully developed a platform for the deposition of innovative "graphitic-like" group III nitrides, which can deliver on novel heterostructure designs," says Anelia Kakanakova, GRIFONE project leader and associate professor at Graphene Flagship Associate Member Linköping University.

References

Dos Santos, Renato B., et al. "Van der Waals stacks of few-layer h-AlN with graphene: an ab initio study of structural, interaction and electronic properties." Nanotechnology 27.14 (2016): 145601.

Kakanakova-Georgieva, Anelia, et al. "Nanoscale phenomena ruling deposition and intercalation of AlN at the graphene/SiC interface." Nanoscale 12.37 (2020): 19470-19476.

Sangiovanni, Davide Giuseppe, G. K. Gueorguiev, and Anelia Kakanakova-Georgieva. "Ab initio molecular dynamics of atomic-scale surface reactions: insights into metal organic chemical vapor deposition of AlN on graphene." Physical Chemistry Chemical Physics 20.26 (2018): 17751-17761.

Pécz, Bèla et al. "Indium Nitride at the 2D limit." Advanced Materials (2020): 2006660.