Effect of substrate microstructure on the misorientation of a-plane ZnO film investigated using x-ray diffraction

Abstract

( 11 2 ¯ 0 ) ZnO (nonpolar a-plane ZnO) films were grown on (11¯02) Al2O3 (r-plane sapphire) substrates by single-source chemical vapor deposition. The misorientation in the film was investigated in detail using x-ray diffraction techniques, including 2θ-ω scan, reciprocal space mapping (RSM), and double- and triple-crystal x-ray diffraction analysis. 2θ-ω scan and RSM measurements suggest that ZnO film grows on r-plane sapphire substrate epitaxially along the [112¯0] orientation, and the (112¯0) plane of the ZnO film tilts with respect to the (11¯02) plane of the substrate. RSM measurement for sapphire substrate shows that the diffraction intensity distribution around (22¯04) reciprocal lattice point presents a curved band along the 2θ-ω scan direction, which can be attributed to a strained layer (or a lattice distortion layer) at the substrate surface. Double- and triple-crystal x-ray diffraction measurements imply that anisotropic mosaic exists in sapphire substrate. The strained layer and tilt mosaic in sapphire substrate may be the important reasons for the tilted growth of the (112¯0) plane of a-plane ZnO film relative to (11¯02) plane of the Al2O3 substrate.