c-plane ZnO on a -plane sapphire: Inclusion of (11¯01) domains

• We investigate the epitaxial growth of (11¯01) oriented ZnO on a-plane sapphire with high resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD).
• We measure a tilt angle of these orientations by approx. 1.45°. In numerical simulations with ANSYS we could confirm this tilt angle of approx. 1.46° at room temperature as a result of strain relaxation during heteroepitaxial growth.
• Due to a good lattice match of these (11¯01) orientations they have a strong influence on the crystal quality of c-plane ZnO films on a-plane sapphire and therefore are responsible for the formation of edge- and screw-type dislocations in c-plane ZnO films.

The influence of metal-free ZnO nanoseed-layers on the growth of ZnO films on a  -plane sapphire substrates by chemical vapor deposition (CVD) is investigated. For epitaxial films with a high density of (11¯01) inclusions we find a twofold orientation of these inclusions with the epitaxial relationships (112¯0)Al2O3∥(11¯01)ZnO and (101¯4)Al2O3∥(0001)ZnO. HRXRD measurements show that these inclusions are tilted by approx. 1.45° towards the sapphire substrate as a result of strain relaxation during heteroepitaxial growth. Numerical simulations with ANSYS confirm this as the energetically favorable situation. Detailed HRXRD and EBSD studies show that the occurrence of (11¯01) oriented nanocrystallites during nucleation is responsible for the formation of dislocations, and that the nucleation process has a pronounced influence on the crystal quality of c-plane ZnO films grown on a-plane sapphire.