The type and distribution of grown-in defects formed in Cz grown silicon depends strongly on the growth parameters, like the furnace design, pull speed and crucible/seed rotation during crystal pulling. From the theory of Voronkov [1] a transition from self-interstitial rich material to a vacancy rich material happens when the v/G ratio (v is the growth rate and G is the thermal gradient) at the solidification front reach a critical value. The material quality from material that is solidified under conditions close to a critical v/G ratio can vary strongly from almost defect free (denuded zone) to regions where large oxygen precipitates are formed (OiSF-ring or p-band). A large problem for the solar cell producers is that the oxygen precipitates formed in the p-band often acts as recombination centres and decrease the efficiency of the solar cell significantly [2, 3]. Effort should therefore be use on investigations of the relation between growth conditions and the formation of the p-band and how it is possible to reduce its negative impact.

The aim of this work is to combine numerical and experimental techniques to study the effect of growth rate variations on the defect formation. Therefore, two n-type Cz-Si ingots have been grown with varying growth rates. Pull speed has been varied to cover different growth regimes. Experimental methods used for characterization of the p-band were Cu-decoration, wet oxidation flow by preferential etching [4]. Numerical simulations of the growth of the two crystals have been achieved. The predicted position of the p-band has been compared to the experimental observation and discussed. 

 References

[1] V.V. Voronkov, J. Crystal Growth 59 (1982) 625.

[2] J. Haunschild, J. Broisch, I. E. Reis, S. Rein, 26th European PV Solar Energy Conference and Exhibition, 5-9 September 2011, Hamburg, German

[3] J. Haunschild, I.E. Reis, J. Geilker, S. Rein, Phys. Status Solidi RRL. 5 (2011) 199-201.

[4] M. Juel, Y. Hu, V. S. Koien, M. Jomâa, S. Zhang, E. Øvrelid, The 6th International workshop on Crystalline Silicon for Solar Cells, October 8-11, 2012, Aix-les-bains, France.

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