Crystal Orientation of Cubic NiO Thin Films Formed on Monoclinic β-Ga2O3 Substrates

The crystal orientation relationship between cubic NiO and monoclinic beta-Ga2O3 in NiO thin films formed on (2 over bar 01), (010), and (001) beta-Ga2O3 substrates is investigated by X-ray diffraction analysis and cross-sectional transmission electron microscopy imaging. The NiO films formed on (2 over bar 01) and (010) beta-Ga2O3 substrates satisfy the orientation relationships NiO (111) [01 over bar 1] || beta-Ga2O3(2 over bar 01) [010] and NiO (110) [1 over bar 10] || beta-Ga2O3 (010) [001], respectively. In the NiO films on (001) beta-Ga2O3 substrates, the NiO plane near (133) is parallel to the (001) plane of beta-Ga2O3 under the relationship NiO [01 over bar 1] || beta-Ga2O3 [010]. In addition, NiO films also satisfy the relationship NiO (100) || beta-Ga2O3 (100) in each case. That is, for each case of (2 over bar 01), (010), and (001) beta-Ga2O3 substrates, the relationship of NiO (100) [011] || beta-Ga2O3 (100) [001] is confirmed, consistent with the orientation relationship reported previously for NiO films on (100) beta-Ga2O3 substrates. The crystal orientation relationship is discussed in terms of the atomic arrangement models of NiO and beta-Ga2O3.