Optical characterization of structurally graded Si1−xGex:H thin films

High efficiency thin film silicon solar cells consist of multiple junctions with hydrogenated amorphous silicon, silicon germanium alloys, and nanocrystalline silicon (nc-Si:H) absorbers. Uniformity over large areas is challenging for nc-Si:H and an accurate method of mapping material quality via a technique like ex situ spectroscopic ellipsometry (SE) is desirable. In situ, real time SE (RTSE) measurements during growth show material evolves from amorphous to nanocrystalline, which complicates the analysis of single SE measurements. Information from RTSE has been applied to develop procedures to accurately extract the thickness at which nanocrystallites initially appear and coalesce from single SE measurements.