Influence of Extended Defects and Native Impurities on the Electrical Properties of Directionally Solidified Polycrystalline Silicon

Abstract

The electrical properties of dislocations and grain boundaries (GB) in directionally solidified polycrystalline silicon were extensively studied as a function of the carbon, oxygen, and nitrogen content, as well as of the relative grain orientation. As a first result of this study we obtained the experimental evidence that the oxygen and carbon content are not independent variables of the material. Therefore, the density and the electrical activity of dislocations are shown to be strongly dependent on the amount of oxygen‐carbon compensation. As a second result, experimental evidence was also achieved which demonstrated that grain boundaries are strongly passivated and that recombination losses at GB do not present any relevant relationship with mutual crystallographic orientations of the grains. It appears, therefore, that a careful choice of the growth and postgrowth conditions yields a material which behaves like crucible grown single‐crystal silicon.

Characterization of mc-Si directionally solidified in travelling magnetic fields

“…A major issue to look at is the presence of oxygen, carbon and nitrogen impurities. For instance it is well known that an increase of oxygen and a decrease of the carbon concentration result in lower dislocation densities [9]. Main sources of the carbon impurity concentrations are the feedstock and the graphite made hot-zone of the furnace, while oxygen may dissolve from the silica crucible.…”

Carbon concentration and particle precipitation during directional solidification of multicrystalline silicon for solar cells

“…When the content of carbon exceeds its solubility limit in silicon, it will precipitate to form silicon carbide (SiC) particles in a directional solidification process. It has been experimentally proved that dislocation density is a function of carbon concentration in multicrystalline silicon [4]. SiC precipitates can cause severe ohmic shunts in solar cells [5] and result in nucleation of new grains in silicon ingots.…”

The carbon distribution in multicrystalline silicon ingots grown using the directional solidification process

“…One of the major impurities in silicon feedstock is carbon. Pizzini et al [3] showed that the density and electrical activity of dislocations in an mc-Si ingot is strongly dependent on the carbon concentration [4]. The carbon concentration in the silicon crystal is lower than the one in the silicon melt, because the segregation coefficient of carbon is less than one [4,5].…”