Metal-organic chemical-vapor deposition of (Ba,Sr)TiO ₃: Nucleation and growth on Pt-(111)

Thin films of the (Bax Sr1-x) TiO3 (BST) solid solution series were grown by metal-organic chemical-vapor deposition (MOCVD) on platinized silicon wafers with emphasis to (Ba0.7 Sr0.3) TiO3 and SrTiO3. The nucleation behavior and the size of the stable nuclei were investigated by different scanning probe microscope techniques including local conductivity scanning. The characteristic differences were observed for different deposition temperatures, i.e., a homogeneous nucleation of small BST grains on the larger Pt grains at 565 °C and a dominating grain-boundary nucleation at 655 °C. X-ray photoelectron spectroscopy indicates a stoichiometric composition from the beginning. The microstructural evolution was investigated by high-resolution transmission electron microscopy and revealed randomly oriented grains (typical in-plane size 10-20 nm) with a high density of twins at 565 °C and (100)-oriented defect-free grains of slightly increased size at 655 °C. This remarkably stable (100) texture seems specific for MOCVD as it is not observed for other deposition methods. The grain structure and surface morphology and their dependence on film stoichiometry (group-II/Ti ratio) are investigated. The relation between the structural and the electrical properties, capacitance, and leakage current, is finally discussed.