Nitride alloys are key materials for solid state lighting and high power electronics. Van der Waals epitaxy of nitrides on 2D materials has attracted a strong interest because it can offer a possibility to reduce the defects generated from the lattice mismatch with conventional substrates and at the same time provides a way for an easy layer lift-off and transfer. It this presentation we investigate the growth of GaN nanowires (NWs) on graphene by molecular beam epitaxy. X-ray diffraction and electron microscopy reveal that the graphene

imposed the vertical and in-plane NW orientations, with (10-10) facets of GaN aligned with graphene zigzag edges [1]. The in-situ analyses of the nucleation stage demonstrate that just after nucleation the GaN nanocrystals are under tensile strain and they relax as growth proceeds [2].

Next, we present a new approach to achieve selective area growth of GaN NWs using graphene nano-patches as preferential nucleation sites. The graphene nano-patches consist of CVD-grown monocrystalline nano-domains or of large domains nanopatterned by lithography. Under proper conditions, the GaN growth is highly selective: NW nucleation does not occur on SiO2 whilst the graphene patches play the role of nano-substrates for GaN NW growth [3]. Finally, we describe the optical properties of the NWs. Photoluminescence spectra of GaN NWs grown on graphene are dominated by D0XA emission with a sub-meV linewidth, which is similar to the best reported broadening for GaN NWs on conventional substrates. The 3.45 eV line, attributed to inversion domain boundaries and present in GaN NWs grown on standard AlN/Si substrates, is not observed in NWs on graphene [4].

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[1] V. Kumaresan et al., “Epitaxy of GaN Nanowires on Graphene” Nano Letters 6, 4895 (2016).

[2] C. Barbier et al. “In Situ X-ray Diffraction Study of GaN Nucleation on Transferred

Graphene” Cryst. Growth & Design 20, 4013 (2020).

[3] M. Morassi et al., “Selective area growth of GaN nanowires on graphene nanodots”, Cryst.

Growth & Design 20 552 (2020).

[4] L. Mancini et al., "Optical properties of GaN Nanowires grown on chemical vapor deposited

Graphene" Nanotechnology 30, 214005 (2019).