Rеvuе des Energies Renouvelables
Volume 14, Numéro 4, Pages 665-674
2011-12-31

Improvement Of Charge Carrier Lifetime In Heat Exchange Method Multicrystalline Silicon Wafers By Extended Phosphorous Gettering Process



Authors : Bouhafs D. . Boumaour M. . Moussi A. . Abaïdia S.e.h. . Khelifati N. . Palahouane B. .

Abstract

External phosphorous diffusion gettering were applied using homogenous and extended schemes on multicrystalline silicon (Mc-Si) wafers obtained from solar grade (SOG) silicon feedstock by the heat exchange method (HEM) growth technique. X-ray fluorescence (XRF) characterization shows the presence of transition metals like Chromium (Cr), manganese (Mn) and iron (Fe) in the analyzed as-cut Mc-Si substrates with a predominance of Mn and Fe elements. Before and after gettering process, we have observed that the Cr atoms concentration drop from 4.1015 at.cm-3 in the as-cut Mc-Si samples to 2.5 1015 at.cm-3 with homogeneous gettering and to 3.1014 at.cm-3 in the wafer undergoes extended gettering. The quasi-steady-state photo conductance (QSSPC) technique is used to characterize the minority charge carrier’s lifetime τn before and after gettering process. It was found that the response of Mc-Si wafers is better (form point of view of lifetime improvement) to the extended process but in some regions it is less effective and the homogenous process give the best amelioration due probably to the spatial distribution of crystalline defects and metallic precipitates densities. With τ n initial values before gettering in the range of 2.5-8 μsec, we have measured lifetime values in the range of 15 to 37 μsec with extended process and from 10 to 30 μsec with the homogenous one which ensure cell efficiencies in the range of 15 to 16%.

Keywords

Multicrystalline silicon, Gettering, Metallic impurities, Lifetime carrier.

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