Optical Properties Of Several Kinds Of Information Functional Films Studied By Spectroscopic Ellipsometry

The development of nanotechniques and nano-scaled thin films is revolutionizing the microelectronic and optoelectronic applications. As one type of important optical characterization methods, spectroscopic ellipsometry (SE) is popularly used to provide useful information about optical constants, nanostructures for nano-scaled thin film, etc. This work mainly focuses on the evolution of optical properties studied by SE, for the information-functional films with different temperatures, structures, thicknesses, compositions, and so on, including the following three parts:1. The temperature dependent optical properties of Sn thin film from solid to liquid are studied by SE and ab initio molecular dynamics (MD) simulations. The real part of dielectric function in liquid Sn is much lower than that in solid, and an interband transition near 1.5 eV is easily observed in solid while it apparently disappeares upon melting. From the evolution of optical properties with temperature, an optical measurement to acquire the melting point by SE is presented. From first principles calculation, we show that the local structure difference in solid and liquid is responsible for this big difference in the optical properties observed in experiment.2. An effective method for determining the optical constants of Ta2O5 thin films with thickness range of 1-400 nm deposited on c-Si using SE measurement is presented. The refractive indices of Ta2O5 ultrathin films less than 40 nm drop with the decreasing thickness, while the other ones are close to those of bulk Ta2O5. This phenomenon is due to the existence of an interfacial oxide region and the surface roughness of the film, which is confirmed by the measurement of atomic force microscopy (AFM).3. Evolving optical properties of Bi1-xSex thin films with different stoichiometry are investigated by SE. A significant dispersion of penetration depth with Bi1-xSex thin films is observed, which will lead to a varying carrier concentration with the different wavelength because of the topologically protected surface state. To describe the special properties of topological insulators, dispersive plasma energy is introduced into traditional dielectric function model. Optical properties of Bi0.38Se0.62 film are acquired by this modified model and the topologically protected surface state can be represented from the dispersion properties of free carrier concentration with the smaller plasma energy versus the deeper penetration depth. We demonstrate that SE is a useful tool for characterizing the properties of the topological insulators.