Effect of Roughness on Ellipsometry Analysis

Abstract

In spectroscopic ellipsometry (SE), appropriate modeling of surface roughness structures is critical for the accurate characterization of optical constants. In particular, when a simple SE analysis is performed for rough surfaces with dimensions comparable to the SE measurement wavelengths (>300 nm), the optical response of the rough surfaces cannot be expressed properly, leading to serious overestimation of absorption coefficients of solar cell materials. Accordingly, extra care is necessary when samples with rough surfaces are analyzed. Large discrepancies observed between reported dielectric functions of CuInSe₂ and CH₃NH₃PbI₃ are found to originate from underestimated roughness contributions, induced primarily by oversimplification of optical models. Quite fortunately, analysis errors generated by the roughness components can be corrected rather easily based on a simple procedure, referred to as extra roughness correction. When this correction scheme is applied, all the dielectric functions and absorption spectra show excellent agreement. It is further demonstrated that the analytical treatment of roughness in SE influences the optical simulation result of solar cells. In this chapter, we will examine the effect of roughness on SE results and discuss the proper SE analysis method for solar cell materials.