Dielectric Functions of Niobium Doped Bi_3.25La_0.75Ti₃O₁₂ Thin Films Using Spectroscopic Ellipsometry

Abstract

Ferroelectric thin films of Nb doped Bi_3.25La_0.75Ti₃O₁₂ (BLT) were prepared by chemical solution deposition method onto Pt/Ti/SiO₂/Si(100) substrates using spin coating technique. From the X-ray diffraction analysis it was found that films were polycrystalline with single phase. The optical properties of the Nb doped BLT thin films were investigated at room temperature in the 0.72–6.2 eV energy range using spectroscopic ellipsometry (SE). Double Tauc–Lorentz (DTL) dispersion relation was successfully fitted in the uv/visible region. Value of the full width at half maxima (Г) in dielectric function plots increased with Nb doping. This increase in FWHM may be attributed to the increase in the trap density in forbidden band which consequently decreases the value of E_g. The optical band gap energy (E _g ^d) was found to decrease with increase in Nb doping concentration. This decrease in E _g ^d with doping may be due to the changes in the defect concentration present in the structure.

Keywords:

• BLT thin films
• Optical materials and properties
• spectroscopic ellipsometry

Acknowledgment

One of the authors (Prikshit Gautam) is thankful to the Inter-University Accelerator Centre (IUAC), New Delhi, India for providing financial support through Project No.UFUP-37310/3797, Dr. Amitabh Basu (NPL, Delhi, India) for ellipsometry measurements.