Dispersion properties in the visible range of carrier concentration of topologically protected Bi1-xSex films revealed by spectroscopic ellipsometry

•A significant dispersion of penetration depth with Bi0.38Se0.62 films versus phonon energy was found.•A dispersive plasma energy was introduced to traditional MDF model for modelling topological insulators.•Spectroscopic ellipsometry was shown to be a useful tool for characterizing the properties of the topological insulators.