Electrodeposition of ZnO nanorod arrays on ZnO substrate with tunable orientation and optical properties

The electrodeposition of ZnO nanorods on ZnO:Al films with different orientations is reported. The influence of the total charge exchanged during electrodeposition on the nanorod's geometry (length, diameter, aspect ratio and surface density) and the optical transmission properties of the nanorod arrays is studied on a {0001}-oriented ZnO:Al substrate. The nanorods are highly vertically oriented along the c axis, following the lattice matching with the substrate. The growth on a {101̄0} and {112̄0} ZnO:Al-oriented substrate with c axis parallel to the substrate leads to a systematic deviation angle of 55° from the perpendicular direction. This finding has been explained by the occurrence of a minority orientation with the {101̄1} planes parallel to the surface, with a preferential growth on corresponding {0001} termination. Substrate crystalline orientation is thereby found to be a major parameter in finely tuning the orientation of the nanorod array. This new approach allows us to optimize the light scattering properties of the films.