Impact of transferred and directly grown graphene on the epitaxial growth of κ-Ga2O3 layers

Remote epitaxy on graphene offers a route to overcome lattice-mismatch constraints and enable the exfoliation of functional semiconductor layers. Metastable κ -Ga 2 O 3 films were grown by pulsed laser deposition on wet-transferred graphene (TGR) covering α -Al 2 O 3 , GaN, and AlN templates and on directly grown graphene (DGR) on sapphire. The films were compared to assess how the graphene interface affects film growth. X-ray diffraction revealed only κ -Ga 2 O 3 reflections and showed that the films maintained in-plane alignment with their respective substrates regardless of graphene type. However, films grown on TGR exhibited dense needle-shaped defects and root-mean-square (RMS) roughness exceeding 70 nm. Transfer-related surface features covered 12–16% of the TGR surfaces, compared with 0.8% of the DGR surface. These features may serve as heterogeneous nucleation sites, promoting Volmer–Weber island growth while preserving crystallographic orientation. In contrast, DGR preserved the substrate step–terrace structure and supported two-dimensional growth. Films grown on DGR had smooth surfaces (RMS ≈ 4.3 nm) and crystalline quality comparable to that of films grown directly on bare templates. Interfacial quality, primarily the absence of transfer-related residues and potentially the crystallographic order of DGR, appears to govern film morphology more strongly than the mere presence of graphene. Thus, DGR offers a promising platform for the epitaxial growth of smooth, metastable oxide films on graphene.