Multicrystalline silicon (mc-Si) is one of the most important substrate materials for solar cells. The efficiency of the processed cells depends strongly on the concentration of impurities and structural defects in the material.  A detailed understanding of defect-related phenomena is necessary to control and reduce the concentration of defects in mc-Si crystals, which is the major challenge crystal growers are faced with. For a successful defect engineering, however, still too little is known about the mutual interaction between impurities, precipitates and dislocations during crystal growth as well as about the correlation between the formation of defects and growth conditions.

This paper presents results on the correlations between impurities, precipitates, and dislocations in mc-Si crystals grown from well-mixed and poorly mixed melts. The crystals were grown in a high-vacuum induction furnace by the vertical Bridgman method. The melt mixing was modified by changing the growth rate and the intensity of the melt flow. The crystals were sliced into vertical and horizontal samples, which were polished and etched to detect impurities, precipitates and dislocations. The impurity concentration was measured by FTIR spectroscopy. Precipitates and dislocations were analyzed by reflected light and IR-transmission microscopy. SEM and EDX were used to detect the morphology and composition of precipitates.

The results show that the formation of precipitates can be completely suppressed in growth from a well-mixed melt, whereas extended precipitated areas are observed in crystals grown from a poorly mixed melt. Mainly SiC and Si₃N₄  precipitates are found. Apparently, they are formed when the melt becomes supersaturated by carbon and nitrogen in front of the interface due to axial segregation during growth under poor mixing conditions. Within precipitated areas the dislocation density is increased, too. Often, a high dislocation density was detected in the direct neighborhood of a precipitate. This demonstrates that precipitates are an important source of dislocations in mc-Si.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29125 must be provided.