Improved method for determining the optical constants of thin films and its application to molecular-beam-deposited polycrystalline layers

Polycrystalline, dielectric thin films are grown by the ultrahigh vacuum technique of molecular-beam deposition. A method of calculating the optical constants of such weakly absorbing, homogeneous layers from spectral transmission information alone, with no prior knowledge of their characteristics, is presented. Initially, the procedure uses transmission turning-point data to estimate refractive index and thickness by an analytical approach. These data are then fitted to a function that undergoes an iterative refinement routine by means of a weighted figure of merit to determine with good accuracy the film parameters as functions of wavelength. In this way the optimum conditions for the deposition of materials such as ZnS, ZnSe, LiF, CaF₂, and BaF₂ are found.