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1

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

100%

Bouhafs D., Khelifati N., Kouhlane Y.

Acta Physica Polonica A

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2016

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vol. 129

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issue 4

690-693

EN

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 (τ_{eff}) 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 τ_{eff} 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 τ_{eff} (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 τ_{Cr-Impurity} lifetime value of about 8.5 μs is extracted, which is the result of interstitial Cr_{i} or Cr_{i}B_{s} pairs, proving their strongest recombination activity in silicon.

2

Adequate Method for Decoupling Bulk Lifetime and Surface Recombination Velocity in Silicon Wafers

76%

Khelifati N., Bouhafs D., Mebarek-Azzem A., El-Hak Abaidia S., Palahouane B., Kouhlane Y.

Acta Physica Polonica A

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2016

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vol. 130

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issue 1

188-190

EN

In this paper, we present an appropriate method of decoupling surface and bulk recombination processes in silicon wafers. The study was carried out using the surface passivation of multicrystalline silicon wafers by ethanolic solution of iodine at different molarities varying between 0.01 M and 0.1 M. The effect of the concentration of ethanolic iodine solution on surface passivation effectiveness was investigated by using quasi steady state photo-conductance technique. Reproducible experiments have shown that the best passivation is reached for a molarity of around 0.02 M. The carrier lifetime after passivation at 0.02 M has been improved by more than one order of magnitude, compared to that of the same wafer before the passivation. Using an adequate modeling of minority carrier lifetime curves τ (Δ n), based on Hornbeck-Haynes model, surface recombination velocity was calculated. The minimum values of surface recombination velocity have been found to be approximately 120 cm/s for 0.02 M. The modeling results indicate that the minority carrier lifetime improvement can be easily correlated with the decrease of the surface recombination velocity for a fixed bulk lifetime τ_{b}=115 μs.

3

Investigation of Degradation of Electrical Properties after Thermal Oxidation of p-Type Cz-Silicon Wafers

76%

Maoudj M., Bouhafs D., Bourouba N., Khelifati N., El Amrani A., Boufnik R., Hamida Ferhat A.

Acta Physica Polonica A

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2017

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vol. 132

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issue 3

725-727

EN

In this study we conducted thermal oxidation of Czochralski p-type <100> silicon wafers. The oxidation was carried out at temperatures in the range of 850-1000°C, in a gas mixture of N₂:O₂, in order to deposit a thin layer (10 nm) of thermal silicon dioxide (SiO₂), generally used in the surface passivation of solar cells. The measurements of effective minority carriers lifetime τ_{eff} using the quasi-steady-state photoconductance have shown degradation of different samples after oxidation process. The calculation of surface recombination velocity after the oxidation process at different temperatures, gave the same value of 40 cm s¯¹, showing a low surface recombination velocity and, therefore, a good surface passivation. Finally, a study based on sample illumination technique, allowed us to conclude that our samples are dominated by bulk Shockley-Read-Hall recombination, caused by Fe-related centers, thereby causing the degradation of the lifetime of minority carriers.

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3 Acta Physica Polonica A

1 2017

2 2016

3 Bouhafs D.

3 Khelifati N.

2 Kouhlane Y.

1 Boufnik R.

1 Bourouba N.

1 El Amrani A.

1 El-Hak Abaidia S.

1 Hamida Ferhat A.

1 Maoudj M.

1 Mebarek-Azzem A.

1 Palahouane B.

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

Adequate Method for Decoupling Bulk Lifetime and Surface Recombination Velocity in Silicon Wafers

Investigation of Degradation of Electrical Properties after Thermal Oxidation of p-Type Cz-Silicon Wafers