Stress-strain state in alpha-Ga2O3 epitaxial films on alpha-Al2O3 substrates

We consider the stress-strain state in alpha-Ga2O3/alpha-Al2O3 heterostructures, in which both constituting phases belong to trigonal crystal system. We utilize the hexagonal geometry (hexagonal cell) to account for structural features of the materials and include in the analysis the complete set of six elastic constants C-ij being typical for materials with rhombohedral crystal structure that differs from materials with hexagonal one by the presence of an additional constant C-14. This allows us to derive analytical formulas for elastic strains and mechanical stresses in pseudomorphic alpha-Ga2O3 films on alpha-Al2O3 substrates with various growth orientations assuming nonzero constant C-14.