Mosaic structure in epitaxial thin films having large lattice mismatch

Epitaxial films having a large lattice mismatch with their substrate invariably form a mosaic structure of slightly misoriented sub-grains. The mosaic structure is usually characterized by its x-ray rocking curve on a surface normal reflection but this is limited to the out-of-plane component unless off-axis or transmission experiments are performed. A method is presented by which the in-plane component of the mosaic misorientation can be determined from the rocking curves of substrate normal and off-axis reflections. Results are presented for two crystallographically distinct heteroepitaxial systems, ZnO, AlN, and GaN (wurtzite crystal structure) on $c$ -plane sapphire and MgO (rock salt crystal structure) on (001) GaAs. The differences in the mosaic structure of these films are attributed to the crystallographic nature of their lattice dislocations.