Modeling the dielectric functions of silicon-based films in the amorphous, nanocrystalline and microcrystalline regimes

We describe simple expressions that use a minimum number of free parameters to fit the dielectric function spectra of a variety of Si-based film materials ranging from amorphous silicon (a-Si:H) and its alloys with Ge and C to nanocrystalline silicon (nc-Si:H) and microcrystalline silicon (mu c-Si:H). Three applications of these formulas are presented. First, we demonstrate how the expressions can be used in optical modeling of multijunction solar cells. Second, we analyze a-Si:H materials prepared Versus the H-2-dilution flow ratio, R = [H-2]/[SiH4], and observe that improved ordering is obtained at larger R. Finally, we analyze Si films as a function of thickness across the a --> mu c phase boundary and quantify effects of electronic confinement in the nc-Si:H regime and grain development in the pc-Si:H regime. (C) 2000 Elsevier Science B.V. All rights reserved.