Investigation of the dopes segregation at the grains boundaries of polycrystalline silicon films for photovoltaic application

The mechanism of the dopes segregation supposes the accumulation of a part the dope at the grain boundaries where it becomes electrically inactive. More over the dopes segregation induces important structural changes in the material constituent the grains boundaries, by reducing the bounding forces between the atoms, by favouring the concentrations of constraints and by preventing the vanishing of dislocations. In this work we investigate the dopes segregation at the grain boundaries in the polycrystalline silicon films. The obtained results have shown that the heat treatments before and/or after implantation reduce the number of segregation sites at the grains boundaries, and consequently they limit the structural changes that can appear and the quantity of dope atoms that can accumulate in these boundaries. In addition they are more and more supplementary dope atoms that are found inside the grains when the temperature of the heat treatment increases. On the other hand, we established that arsenic atoms have a strong tendency to the segregation than the bore atoms, and we have noticed a strong migration of arsenic atoms from the boundaries towards the grains under the effect of the heat treatments. More over it was found that the concentration of arsenic atoms in the boundaries NGB is more and more high when the doping increases. However the ratio NGB/N relative to the dope average concentration decreases.