Strain Relaxation of Al‐Rich α‐(AlGa)₂O₃ and α‐Al₂O₃/Ga₂O₃ Superlattice on <i>m</i>‐Plane Sapphire Substrates by Plasma‐Assisted Molecular Beam Epitaxy

Abstract The strain relaxation of Al‐rich α‐(Al x Ga 1‐ x ) 2 O 3 single layers with x &gt; 0.6 and an α‐Al 2 O 3 /Ga 2 O 3 superlattice structure grown on m ‐plane sapphire substrates by molecular beam epitaxy is investigated. Symmetrical full‐width half maximum values of X‐ray diffraction (XRD) omega scans are less than 400 arcsec for pseudomorphically grown α‐(AlGa) 2 O 3 single layers, but increase significantly as compressive stresses in the α‐(AlGa) 2 O 3 layers are released due to lattice relaxation. Transmission electron microscopy (TEM) for a partially relaxed sample reveals the formation of V‐shaped dislocations with screw components on the sample surface, while the initial interface layer exhibits a low dislocation density, as the V‐shaped dislocations do not completely extend to the epilayer/substrate interface. The variation in dislocation density in the α‐(AlGa) 2 O 3 layer results in two distinct XRD peaks. The TEM observation suggests the most probable relaxation system of . Scanning TEM observation for the α‐Al 2 O 3 /Ga 2 O 3 superlattice structure reveals that the α‐Ga 2 O 3 layers are grown in the Stranski‐Krastanov (SK) mode.