Abstract

The optical constants of thin-film materials can be determined from measurements of the reflectance R and the transmittance T of a single layer film deposited on a transparent substrate. If the film is homogeneous and absorbing and is thick enough to have several maxima and minima, the index n and extinction coefficient k can be determined from T alone using the envelope method. If the film is inhomogeneous but nonabsorbing, the degree of inhomogeneity and index can be determined from R alone. This determination is based on the assumption that the inhomogeneous index of the film varies smoothly from a value of n₁ at the outer surface of the film to a value of n₂ at the substrate surface of the film. When the film is both inhomogeneous and absorbing, both R and T are necessary for the determination of the optical properties. The solution is most easily obtained in terms of the degree of inhomogeneity α = √(n₂/n₁. If the absorption in the film is <5 %, α can be determined from the reflectance scan independently of n and k. Then, n and k can be determined from the transmittance scan using the measured value of α. For more highly absorbing films, the values of n and k can be used to obtain a more accurate measure of α and the procedure can be iterated to find the best solution. The algorithm is applied to films of Sc₂O₃ which were measured as part of a comprehensive study presented at the 1983 OSA Annual Meeting.¹

© 1986 Optical Society of America