Silicon tubes by a closed molten zone: a characterisation study

We report on the characterisation of silicon tubes recrystallised by closed molten zone, a technique developed as a step to a possible process for thin silicon sheet production. The tube faces are quite flat and have a smooth surface. For the electrical characterisation, samples were cut from the tube faces and simple photovoltaic solar cells were formed. The average diffusion length of minority carriers was found, from spectral response, to be around 100 μm. Low-resolution LBIC measurements showed lower diffusion lengths (around 40 μm) in the regions close to the tube edges. This behaviour was correlated to measurements of residual thermal stresses using infrared photoelasticity. Measurements of the changes of spectral response with increasing bias light intensity reveal an increase in the effective diffusion length, a known effect that is interpreted in terms of a density of trapping states.