Distribution of Light Elements in Multicrystalline Silicon for Solar Cells Grown by Directional Solidification

Abstract

We investigated the relationship between the formation of small grains and the distribution of precipitates such as Si3normalN4 and SiON in a multicrystalline silicon ingot grown by the unidirectional solidification method. Si3normalN4 precipitates were mainly observed inside the small grain region, while SiON was mainly precipitated outside the small grain region. SiON started to precipitate before the formation of Si3normalN4 precipitates. Therefore, precipitation of SiON before precipitation of Si3normalN4 is a candidate in the formation of small grains.

Formation of Si2N2O Microcrystalline Precipitates near the Quartz Crucible Wall Coated with Silicon Nitride in Cast-Grown Silicon

“…The existence of the Si 2 N 2 O phase of silicon oxynitride in multicrystalline Si was previously suggested. [7][8][9][10] However, it has not yet been determined whether these precipitates are amorphous or crystalline and whether their stoichiometry is in fact Si 2 N 2 O. In the present study, we show crucial evidence of the formation of stoichiometric Si 2 N 2 O microcrystalline precipitates inside of the Si ingot.…”

“…Lu et al 7) observed broad absorption peaks at 900-1005 cm À1 , suggesting that silicon oxynitrides with different nitrogen/oxygen ratios exist in their sample. Moreover, Matsuo et al 9) observed the infrared peak of silicon oxynitride in cast-grown multicrystalline Si and determined the composition from the peak position to SiN 1:1 O 0:36 , which is rather close to Si 2 N 2 O. However, these studies discussed the chemical reactions on the basis of amorphous silicon oxynitride.…”

“…On the other hand, Si 2 N 2 O can be formed by a reaction between SiO and N 2 near the crucible wall. According to the thermodynamic phase diagram of the SiO 2 -Si 3 N 4 system, [7][8][9]20) SiO 2 appears if the oxygen partial pressure in Si is high and Si 3 N 4 appears if the nitrogen partial pressure is high. Under the condition that both the partial pressures of N and O are high, Si 2 N 2 O would be formed according to…”

Complementary Distribution of NN and NNO Complexes in Cast-Grown Multicrystalline Silicon for Photovoltaic Cells

“…6) Recently, many researchers have studied O, C, and N precipitates in mc-Si by Fourier transform infrared spectroscopy (FTIR). [7][8][9][10] Lu et al 9) investigated the relationship between the N precipitates, Si 3 N 4 , and the O precipitates, SiO 2 , in polycrystalline sheet silicon. Precipitates consisting of N and O, such as the oxynitride Si 2 N 2 O, have also been reported.…”

“…Precipitates consisting of N and O, such as the oxynitride Si 2 N 2 O, have also been reported. 10) However, the formation mechanisms of the N precipitates such as Si 3 N 4 and Si 2 N 2 O have not yet been elucidated.…”