Structural characterization of ZnO nanopillars grown by atmospheric-pressure metalorganic chemical vapor deposition on vicinal 4H-SiC and SiO2/Si substrates

摘要

The structural characteristics of ZnO nanocrystals epitaxially grown on p-type (0001) 4H-SiC substrates were studied by transmission electron microscopy (TEM). The nanocrystallites were grown by atmospheric-pressure metalorganic chemical vapor deposition. The ZnO nanocrystals were formed at terraces introduced by vicinal 4H-SiC substrates toward the [11 (2) over bar0] direction. They had the shape of hexagonal nanopillars, with their edges parallel to the andlt; 11 (2) over bar0 andgt; directions and a top c-plane facet, reflecting the crystal symmetry of ZnO. The free surface between the hexagonal nanopillars was covered by a very thin and highly defected epitaxial ZnO film, which strongly suggests the Stranski-Krastanov mode of growth. The ZnO/SiC interface was systematically studied by plane view TEM and cross sectional high resolution TEM. The residual strain in the thin continuous film as well as in the nanopillars was estimated from Moire patterns and by geometrical phase analysis. ZnO was also deposited on the SiO2/Si substrate for comparison. The films were polycrystalline exhibiting strong preferred orientation, with the c-axes of the grains almost perpendicular to the substrate resulting in the formation of nanopillars. The differences of nanopillar formation in the two substrates, 4H-SiC and SiO2 is also discussed.