Growth mechanism for single-crystalline thin film of InGaO3(ZnO)5 by reactive solid-phase epitaxy

The growth mechanism for a single-crystalline film of InGaO3(ZnO)(5) (IGZO) on a (111)-oriented yttria-stabilized-zirconia substrate by reactive solid-phase epitaxy was studied by high-resolution x-ray diffraction, transmission electron microscopy, and atomic force microscopy. We focused on the role of the 2-nm-thick ZnO epitaxial layer during the structural evolution of the 200-nm-thick polycrystalline- (poly-) IGZO layer while thermal annealing. When a thin ZnO epitaxial layer was formed before depositing the poly-IGZO layer, thin single-crystalline epitaxial IGZO seeds were initially formed only on the substrate surface or on the thin ZnO epitaxial layer through a solid-phase reaction between the ZnO epitaxial layer and the poly-IGZO layer. A single-crystalline IGZO layer grew from the IGZO seeds toward the top surface of the film along with a much faster lateral grain growth, which formed a large-area single-crystalline IGZO film with an atomically flat terraced and stepped surface. On the other hand, an epitaxial film was not obtained unless a ZnO epitaxial layer was used, demonstrating that the ZnO epitaxial layer plays a crucial role as the seed for subsequent crystallite growth and a template for determining the crystallographic orientation. (C) 2004 American Institute of Physics.