Optimized Temperature in Phosphorous Diffusion Gettering Setup of Chromium Transition Metal in Solar Grade Multicrystalline p-Type Silicon Wafer

D. Bouhafs, N. Khelifati and Y. Kouhlane CRTSE, Division de Développement de Dispositifs de Conversion à Semiconducteurs, 2 Bvd Frantz Fanon, BP 140 Alger 7-Merveilles 16038, Algeria

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We have investigated in this work the effect of the temperature profile during homogeneous phosphorous diffusion gettering (PDG) on multicrystalline (mc-Si) silicon p-type wafers destined for photovoltaic solar cells. Temperatures were varied from 800°C to 950°C with time cycle of 90 minutes. Phosphorous profile of n+p junction was measured by secondary ion mass spectroscopy (SIMS) from 0.45 μm to 2.4 μm. Chromium concentration profile measured on the same samples by SIMS shows a high accumulated concentration of Cr atoms in the gettering layer at 900°C and 950°C, compared to samples obtained at 800°C and 850°C. The effective lifetime (τeff) of minority charge carriers characterized by quasi-steady state photoconductance (QSSPC) is in correlation with these results. From the QSSPC measurements we have observed an amelioration of τeff from 7 μs before PDG to 26 μs in the samples after PDG, processed at 900°C. This indicates the extraction of a non-negligible concentration (5×1014 cm-3 to 5×1015 cm-3) of Cr from the bulk to the surface gettering layer, as observed in the chromium SIMS profiles. A light degradation of τeff (18 μs) is observed in the samples treated at 950°C due probably to a partial dissolution of the metallic precipitates, especially at the grain boundaries and in the dislocations vicinity. The related τCr-Impurity lifetime value of about 8.5 μs is extracted, which is the result of interstitial Cri or CriBs pairs, proving their strongest recombination activity in silicon.

DOI: 10.12693/APhysPolA.129.690 PACS numbers: 88.40.jj, 81.05.Bx, 81.65.Tx, 87.15.Pc