Heteroepitaxial growth and characterization of ZnO films on Gd₃Ga₅O₁₂ garnet substrates

ZnO (0001) films have been grown epitaxially on (111) and (001) planes of Gd₃Ga₅O₁₂ (GGG) substrates, which have different orientations and symmetries. The X-ray diffraction revealed that the out-of-plane and in-plane epitaxial relations of ZnO films on the GGG (111) substrates [ZnO/GGG (111)] were the [0001]_ZnO || [001]_GGG and [10 − 10]_ZnO || [1 − 12]_GGG ± 21°, while ZnO films on the GGG (001) substrates [ZnO/GGG (001)] showed the out-of-plane and in-plane epitaxial relations with the [0001]_ZnO || [001]_GGG and [10 − 10]_ZnO || [100]_GGG, [010]_GGG. The mosaic spread of ZnO/GGG (001) along the in-plane and out-of-plane directions was larger than that of ZnO/GGG (111), which was closely related to a number of dislocations generated in the ZnO lattices. These mosaic structures mainly determined crystal quality of ZnO films, as also confirmed by transmittance electron microscopy (TEM). Moreover, high-resolution TEM showed that the lattice of ZnO along the [0001] direction was connected with lattices of GGG along the [111] and [001] directions without interface buffer layers. Finally, crystalline quality of ZnO films was also clarified by temperature-dependent photoluminescent spectroscopy. This study contributes to provide a new device concept on oxide semiconductor/garnet interfaces.