Abstract. The position of the absorption edge (the energy where the absorption values begin to differ from zero) is one of the often used characteristics of the material. For thin films, it is usually obtained from transmission or transmission and reflection values of the film using different approximate methods and models to simplify the analysis. A reason for this is that the transmittance and reflectance of the film samples depend not only on the absorption but also on the interference inside a film and on the reflection from the backside of a transparent substrate. For bulk material and thicker films, the interference effects can be ignored, but for films thinner than 1 μm, it can create a real problem. In this study we present the results obtained using the different mathematical approaches to calculate absorption coefficient of a model film and analyze the applicability of these methods. The absorption edge of the atomic layer deposited Hf_xTi_yO_z films using different approximations is calculated and the amount of scattering of resulting values caused by different calculation methods is demonstrated. According to our study, the most appropriate model is the one presented by W.Q. Hong.

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