Determination of Thickness and Optical Parameters of Thin Films from Reflectivity Spectra Using Teaching-Learning Based Optimization Algorithm

Abstract

In this paper, we report a simple method to extract thickness and refractive index of thin-film from experimentally measured reflectivity spectra using teaching-learning based optimization (TLBO) algorithm. The algorithm finds thickness and refractive index by fitting an experimentally measured reflectivity spectra with theoretically ones generated by transfer matrix approach. The value of refractive index as a function of wavelength is determined by considering sellmeier dispersion relation. The algorithm is implemented by means of an interactive numerical simulation using LabVIEW as a programming tool. To check the effectiveness of the self-developed program, it is tested on different thin-film samples prepared from some commonly used optical materials such as MgF2, Al2O3 and SiO2 using electron beam evaporation technique. The values of thicknesses and refractive index spectra for different thin-film samples obtained by TLBO algorithm are verified using standard spectroscopic ellipsometry measurements. It is found that there is an excellent agreement between the results obtained by the TLBO algorithm and those by ellipsometry. It is also demonstrated that a simple reflectivity measurements give the valuable information about the thickness and dispersive refractive index over a range of wavelengths, which are obtained by our self-developed simulation program based on TLBO algorithm.