Preparation and phase structures of Zn–Ti–O ternary compounds by atomic layer deposition

Zn–Ti–O (ZTO) ternary films with various Zn/Ti cycle ratios were deposited on Si substrates using diethylzinc and titanium isopropoxide as Zn and Ti sources by atomic layer deposition (ALD). The effect of Zn/Ti cycle ratio and postannealing temperature on the growth rate, composition, phase structure, and morphology of ZTO films were investigated by a series of analytical tools. It is found that for ALD ZTO films, the growth per cycle (GPC) of TiO₂ deposited on ZnO-terminated surface is faster than that of pure TiO_2, while the GPC of ZnO deposited on TiO₂-terminated surface becomes slower than that of pure ZnO. This makes the Zn/Ti cycle ratio effect on the film composition become weak. The postannealing temperature and ALD sequence play important roles in facilitating the ZTO phase evolution. Pure Zn₂TiO₄ phase can be obtained in the (1:2)-ZTO films with 40.3 mol. % Ti content postannealed at 900 °C. For (2:5)-ZTO samples with 48.8 mol. % Ti content, pure h-ZnTiO₃ phase can be formed at 700 °C. At 700 °C and above, the rutile TiO₂ phase appears for (1:3)-ZTO samples with 52.1 mol. % Ti content. The scanning electron microscopy images confirm with increasing the postannealing temperature; the grain size becomes large with the inhomogenous morphologic change due to the h-ZnTiO₃ phase decomposition into Zn₂TiO₄ and rutile TiO₂ phases.