Structural insights into nucleation and grain orientation in β-Ga2O3 films grown by MOVPE on off-axis 4H-SiC substrates

β-Ga2O3 film grown on a stepped 4H-SiC substrate exhibiting grains with (-201), (310) and (101) in-plane orientations • β-Ga 2 O 3 films were grown by MOVPE on 4° off-axis 4H-SiC substrates. • TEM and XRD analyses revealed three distinct grain orientations: (20̅1), (101), and (310). • The (-201) orientation dominates, while (101) grains remain confined near the interface. • (310) grains nucleate sparsely but expand laterally up to the film surface. • Step-flow growth is disrupted, favoring 2D nucleation and 3D island formation. In this work, β-Ga 2 O 3 was deposited by low-pressure metal organic vapour phase epitaxy on 4° off-axis 4H-SiC. This substrate has a high thermal conductivity and can enable a more effective heat dissipation in vertical power devices compared to the low-conductivity β-Ga 2 O 3 homo-substrates. The obtained heteroepitaxial films were characterized by X-ray diffraction and transmission electron microscopy. Results show that β-Ga 2 O 3 films are composed of grains with three specific in-plane orientations, all characterized by planes of oxygen atoms arranged in a pseudo hexagonal geometry, namely the (-201), which is the main orientation, the (101), which remains confined near the interface, and the two equivalent (310) and (3-10), which instead tend to expand laterally and grow up to the film surface. The interface between β-Ga 2 O 3 and 4H-SiC was thoroughly investigated by electron diffraction and high-resolution scanning transmission electron microscopy. The outcome of this work provides a deeper understanding of the nucleation and growth of β-Ga 2 O 3 on 4° off-axis 4H-SiC substrates, focusing on the competition between step-flow and island growth mechanisms.