Comment on “Stress-strain state in α-Ga₂O₃ epitaxial films on α-Al₂O₃ substrates” [Appl. Phys. Express 13, 075502 (2020)]

A Most General and Facile Recipe for the Calculation of Heteroepitaxial Strain

“…We note that ϵ 0 13 6 ¼ 0 for ϕ ¼ 0, in disagreement with previous studies. [21][22][23][24] The graphic result in a previous study [3] also shows that generally ϵ 0 13 6 ¼ 0 for strained rhombohedral heterostructures (ϵ 0 13 ¼ 0 for θ ¼ 0, AEπ=2 and for ϕ ¼ π=6 þ nπ=3, n ∈ ℤ). Thus, the analytical formulas for ϵ 0 11 and ϵ 0 22 in a previous study [21] are not equivalent to the ones given here for ϕ ¼ 0.…”