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 TiO2, 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.