Evolution of Grain Structures and Morphological Observation of Crystal-Melt Interface during Electric Molten Zone Crystallization of Silicon and Silicon-Germanium Alloy Wafers

The evolution of grain structures, especially the types of grain boundaries (GBs), during directional solidification is crucial to the electrical properties of multicrystalline silicon used for solar cells. To study this, the electric molten zone crystallization (EMZC) of silicon wafers at different drift speeds from 2 to 6 mm/min was considered. It was found that <111> orientation was dominant at the lower drift velocity, while <112> orientation at the higher drift velocity. Most of the non-∑GBs tended to aligned with the thermal gradient, but some tilted toward the unfavorable grains having higher interfacial energies. On the other hand, the tilted ∑3 GBs tended to decrease during grain competition, except at the higher speed, where the twin nucleation became frequent. The competition of grains separated by ∑GBs could be viewed as the interactions of GBs that two coherent ∑3n GBs turned into one ∑3n GB following certain relations as reported before. On the other hand, when ∑ GBs met non-∑ GBs, non-∑ GBs remained which explained the decrease of ∑ GBs at the lower speed. Nakajima et al. has recently proposed multicrystalline SiGe with microscopic compositional distribution as a novel annual photovoltaic material. We also studyed the evolution of grain structures of multicrystalline SiGe at different Ge concentration from 0 to 12.45 at. % was considered. It was found that <111> orientation still was dominant at high Ge concentration. Nakajima et al. has recently proposed multicrystalline SiGe with microscopic compositional distribution as a novel annual photovoltaic material. We also studyed the evolution of grain structures of multicrystalline SiGe at different Ge concentration from 0 to 12.45 at. % was considered. It was found that <111> orientation still was dominant at high Ge concentration.