Structural and optical properties of BaTiO3 thin films prepared by radio-frequency magnetron sputtering at various substrate temperatures

Thin films of BaTiO3 were prepared by radio-frequency magnetron sputtering at substrate temperatures from 450 to 750 degrees C and analysed by x-ray diffraction, optical transmittance and Raman spectroscopy. The packing density of the films relative to the crystalline density increases from 0.75 at 450 degrees C to about I at 750 degrees C. At a substrate temperature of 450 degrees C, the film is nano-crystalline (5 to 20 nm) with big lattice expansion, large band gap and pronounced hexagonal Raman lines. This film is homogeneous in the thickness direction. Films prepared at higher temperatures exhibit perovskite peaks in the Raman spectrum and an optical band gap of 3.38 eV. At 600 degrees C, the film exhibits a pronounced two-phase growth with a porous nucleation layer of initial packing density of 0.78, a preferred (100)-orientation of the grains and minimum micro-strain. At 750 degrees C, the films are again homogeneous in the thickness direction, have nearly crystalline packing density and preferably (110)-oriented grains.