Oxygen precipitate denuded zone in polycrystalline sheet silicon

The spatial variation of oxygen precipitation across the thickness of polycrystalline sheet silicon has been investigated by Fourier transform infrared (FTIR) microspectroscopy and preferential etching/optical microscopy. FTIR shows that interstitial oxygen is depleted near the top surface of the as-grown sample, thereby suppressing oxygen precipitation during subsequent annealing. Preferential etching and electron-beam-induced current imaging of polished cross sections revealed a 250 - μ m -wide precipitate denuded zone near the top surface. Evidently, growth-induced near-surface reduction of the oxygen profile keeps the oxygen supersaturation below a critical level for precipitate nucleation. Considering that the minority carrier diffusion length of current finished sheet silicon solar cells ranges from 50 to 100 μ m , it is anticipated that optimization of the 250 - μ m -wide precipitate denuded zone will improve solar cell performance.