Optical and electrical properties of BaTiO3 thin films prepared by chemical solution deposition

Barium titanate sol was prepared using barium ethyl hexanoate and titanium isopropoxide. The sol was then spin coated on p-type single crystal silicon (100) wafers, stainless steel and fused silica substrates and annealed to give polycrystalline, transparent, and crack-free films. The surface morpho logy and structural properties of the films were studied using scanning ele ctron microscopy and X-ray diffraction respectively. Crystalline phase coul d form only at an annealing temperature of 650 degrees C and above. The eff ect of post deposition annealing on the optical and structural properties a s well as on the band gap were analysed. Transmission spectra were recorded and from this, refractive index, extinction coefficient and thickness were calculated for films on fused silica annealed at different temperatures. T he dispersion curve for the refractive index n of 650 degrees C annealed fi lm is fairly flat beyond 450 nm and rises sharply towards the shorter wavel ength region, showing the typical shape of a dispersion curve near an inter band transition. The present study indicates the validity of the DiDomenico model for the interband transition with a single electronic oscillator. Th e refractive indices lie in the range 1.75-2.5 for films annealed in the ra nge 300-750 degrees C. The electrical measurements were conducted on metal- ferroelectric-semiconductor (MFS) and metal-ferroelectric-metal (MFM) capac itors. The typical measured small signal dielectric constant was 66 and 140 at 1 MHz for the MFS and MFM capacitors respectively. Debye type dispersio n was observed for films on stainless steel substrates with an activation e nergy of about 0.34 eV. The low held ac conduction was found primarily due to hopping of electrons through the trap centres. The I-V characteristics o f the MFS capacitor were found to be ohmic at low fields and space charge l imited at high fields. I-V characteristics of the MFM capacitor showed a st range behaviour, linear dependence of current on voltage up to 10 degrees V /m and V-5/2 dependence beyond 10(6) V/m. (C) 1999 Elsevier Science S.A. Al l rights reserved.