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 x 10(-5) Torr with 6 sccm O-2 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 = lambda/4n, lambda: 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.