Structural and optical properties of Ba0.5Sr0.5TiO3 thin films on single crystalline substrates

The present investigation reports on structural and microstructural information of the Ba0.5Sr0.5TiO3 (BST-0.5) film deposited over single crystalline Si (100), MgO (100), and LaAlO3 (100) substrate using pulsed laser deposition (PLD) method. In this study, initial experiments were carried out by depositing BST-0.5 films at 1023 K and with oxygen partial pressures of 0.13 Pa and 13.33 Pa on Si (100) substrates. X-ray diffraction (XRD) analysis indicated the formation of a highly crystalline perovskite cubic phase for film deposited at substrate temperature 1023 K. Another set of depositions were carried out at the substrate temperature of 873 K and 1023 K and with oxygen partial pressure of 13.33 Pa. The XRD analysis indicated that deposition at 13.33 Pa has produced BST-0.5 films of increased crystallinity at the substrate temperature of 1023 K. Raman spectra obtained for BST thin film deposited on these three substrates confirmed the formation of the cubic phase. BST thin films were also prepared on LaAlO3 (100) and MgO (100) to investigate the optical properties of film prepared under the best deposition conditions such as 1023 K and 13.33 Pa. The bandgap energies were found to be in the range of 3.93-3.97 eV for these substrates. The measurements of optical properties of the BST-0.5 film coated on LaAlO3 substrate showed about ~75% transmittance compared to MgO substrate. Higher extinction coefficient for the BST-0.5 thin film was observed for the film coated on MgO substrate in the UV and visible region compared to that of the film coated on LaAlO3 substrate. The refractive index as a function of wavelength was found to be 1.945 and 2.023 for BST-0.5 thin film coated on MgO and LaAlO3, respectively. The enhanced optical properties of the BST film coated on LaAlO3 substrate are discussed in relation to higher crystallinity and epitaxial growth of thin films obtained because of lower lattice mismatch.