Ellipsometric study of crystallization of amorphous Ge thin films embedded in SiO 2

Abstract

We use spectroscopic ellipsometry to investigate crystallization of amorphous Ge thin films by thermal annealing of SiO 2/ a-Ge/SiO 2 trilayer structures. We study the influence of both film thickness and annealing temperature on the effective dielectric functions of the Ge films, which are related to the film micro- and nanostructures. For annealing temperatures below 900 °C, all films remain continuous and consist of mixtures of amorphous and nanocrystallized Ge. The crystallite sizes can be estimated from the observed energy blueshift of the E 1 interband transition. Samples annealed at 900 °C display dielectric function spectra which differ from a bulk-like behavior. This suggests a variation in optical properties which is correlated to formation of discontinuous films of Ge nanocrystals.