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Corundum-structured α-Ga 2 O 3 epitaxial thin films were grown on c -plane α-Al 2 O 3 (sapphire) substrates by a mist chemical vapor deposition method. To reveal the defect structures, the α-Ga 2 O 3 film was observed by high-resolution transmission electron microscopy (TEM). We found that the α-Ga 2 O 3 thin film was in-plane compressive stressed from the α-Al 2 O 3 substrate. Although misfit dislocations were periodically generated at the α-Ga 2 O 3 /α-Al 2 O 3 interface owing to the large lattice mismatches between α-Ga 2 O 3 and α-Al 2 O 3, 3. 54% (c -axis) and 4. 81% (a -axis), most of the misfit dislocations did not thread through the layer. An extra-half plane was 2̄110 consisting only of Ga. Screw dislocations were not confirmed, i. e. , the density was under 10 7 cm -2. The threading dislocation density was 7 ×10 10 cm -2.
Kaneko et al. (Tue,) studied this question.