Investigation of TiO2–Al2O3 bi-layer films as Bragg reflector of blue light by using electron beam evaporation

In this study, Al₂O₃ and TiO₂ ceramics were used as the targets to deposit the single layer TiO₂ and Al₂O₃ films and TiO₂–Al₂O₃ bi-layer films by electron beam evaporation. The deposition pressure was 4 × 10⁻⁵ Torr with 6 sccm O₂ being introduced into the chamber during the deposition process and the deposition rates of TiO₂ and Al₂O₃ in single and bi-layer films were controlled at 0.10 nm/s. At the first, single layer TiO₂ and Al₂O₃ films were deposited on the glass substrates and the refractive indexes of TiO₂ and Al₂O₃ films at optical wavelength of 450 nm were measured to be 2.20 and 1.74. The values of 2.20 and 1.74 were used for finding the thicknesses matched for the quarter wave of 450 nm (d = λ/4n, λ: targeted wavelength, n: refractive index, and d: film thickness), the thicknesses of TiO₂ and Al₂O₃ films matched for the quarter wave condition were 51 and 64 nm, respectively. TiO₂–Al₂O₃ bi-layer films was defined as a period to fabricate the distributed Bragg reflectors (DBRs) and one, two, four, and six periods of TiO₂–Al₂O₃ bi-layer films were deposited on glass substrates for comparing their physical and optical properties.