ABSTRACT
Al2O3 is a wide band gap dielectric which consists in various crystalline forms. However, amorphous Al2O3 films are used as a passivation layer with a refractive index of about 1.65 at a wavelength of 620 nm. The development of aluminum oxide coatings has been pushed forward by applications as protective layer in the cutting tool industry [R. Funk et al. 1976, S. Ruppi 2005], as tunnel barrier in special thin film structure [S. Oh et al. 2005, A.M. Bataille et al. 2005], and as an insulation layer in semiconductor devices [M. Specht et al. 2005, P.D. Ye et al. 2005]. For optical applications, Al2O3 is mostly deposited by electron beam evaporation, although all the methods mentioned with SiO2 can be applied [P.J. Martin et al. 1999].
