(Pseudo-)symmetry-driven coherent interfaces and texture in epitaxial β-Ga ₂ O ₃ thin films on (001) diamond

Epitaxial β-Ga 2 O 3 films grown on (001) diamond substrates with a β-(Al/Ga) 2 O 3 buffer layer exhibit strong texture with multiple rotational domain variants sharing a common growth axis. This texture is attributed to two interrelated structural and geometrical factors: (1) pseudo-symmetry about the growth direction due to the high symmetry of the oxygen sublattice which results in close interplanar spacings of different lattice planes that determine the in-plane lattice mismatch, and hence two different crystallographic relationships and types of domain variants; (2) the lack of higher-order symmetry in the C 2/ m monoclinic structure of β-Ga 2 O 3 and the higher symmetry of the diamond substrate that leads to various subvariants. The microstructure of the films consists predominantly of domain clusters, with domains rotated by either ∼60° or 120° (±10°) relative to each other about the growth axis ∼[ 1 02]. Some domain boundaries (DBs), visible near edge-on in cross-sectional and plan-view projections, exhibit a high degree of coherency. These highly coherent DBs with small lattice rotation and/or distortion near the DB are observed where small in-plane and off-plane DB lattice mismatch is expected. Larger lattice mismatch between domains is accommodated by relatively large lattice rotation and/or distortion near the DB, as well as changes in DB structure and shape. Understanding the origin of texture and the characteristics of common planar defects in β-Ga 2 O 3 will offer insights into their impact on thermal and electrical transport properties and enable effective microstructural optimization for successful integration into future power electronics.