Electrical properties and boundary structures in cast-grown polycrystalline silicon

Annealing effects on grain boundaries (GBs) in polycrystalline Si (pc-Si) was studied using electron-beam-induced current (EBIC) measurement. Recombination velocities were determined for different boundary structures. Investigated boundary structures were electrically active Σ3, Σ9, Σ27a, and small angle (SA) boundaries. Recombination velocity at SA boundary is greater by an order than those of CSL boundaries. Compared between CSL boundaries in the as-grown wafer, the recombination velocities are greater in higher sigma numbers of GBs. The electrically active SΣ boundary was revealed to consist of two or more twin boundaries with dislocations. Recombination velocities at GBs except Σ27a decreased after annealing at 600 to 800°C. It is suggested that metal impurities diffused out from GBs at these temperatures. After annealing at 1000°C, recombination velocities of all the GBs drastically increased. Precipitation and increase in Secco-etch pit size were observed after annealing.