Spectroscopic ellipsometry studies of thin film CdTe and CdS: From dielectric functions to solar cell structures

Real time, in situ, and ex situ spectroscopic ellipsometry (SE) methods have been applied in systematic studies of the structure and optical properties of polycrystalline CdTe and CdS thin films deposited by rf magnetron sputtering. The goal of this ongoing research is to establish a basic understanding of the relationships between the physical and optical properties, including how the void fraction, grain size, strain, and temperature of measurement affect the complex dielectric function. This goal has been achieved through recent in situ and real time SE determinations of the structural evolution and dielectric functions of CdTe, CdS, and related alloys, in conjunction with in-depth analyses of the dielectric functions and their critical points. With a collection of parameterized dielectric functions and parameters linked to the physical properties, ex situ SE analysis of solar cell structures becomes possible for extracting not only thicknesses, but other useful physical properties as well.