High-precision characterization of textured a-Si:H/SnO2:F structures by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) has been applied for the characterization of hydrogenated amorphous silicon (a-Si:H) layers formed on SnO2:F textured structures in an attempt to establish the structural characterization method for a-Si:H solar cells. In particular, an optical model that allows the complete evaluation of microscopically non-uniform a-Si:H/SnO2:F textured structures has been developed for the SE analysis. In order to express the complicated optical response in the textured structures, the optical model incorporates (i) the surface roughness and interface layers calculated using an effective-medium-approximation multilayer model and (ii) the a-Si:H/SnO2:F structure divided into two regions with different thicknesses. Using this optical model, SE spectra obtained experimentally from the a-Si:H/SnO2:F textured structure can be reproduced almost perfectly. The a-Si:H/SnO2:F structure deduced from the SE analysis shows remarkable agreement with that observed from transmission electron microscopy. Moreover, a variety of a-Si:H layers with different thicknesses are expressed from the identical optical model. The SE analysis method developed in this study can be utilized further to perform high-precision and non-destructive characterization of various a-Si:H layers incorporated in large-area a-Si:H modules. (C) 2011 American Institute of Physics. [doi:10.1063/1.3646521]