Cathodoluminescence assessment of annealed silicon and a novel technique for estimating minority carrier lifetime in silicon

Fraser, Kieth; Falster, R.; Wilshaw, Peter R.

doi:10.1016/j.mseb.2008.05.006

Cited by 6 publications

(5 citation statements)

References 8 publications

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“…Controlling the distribution of iron in mc-Si by optimising thermal processing is necessary to maximise cell efficiency 23,24 and various groups have proposed that long annealing processes at moderate temperatures (300 C to 600 C) could improve overall performance by redistributing metallic impurities. [25][26][27] Although such studies have shown empirical improvements, the precise details of what happens to the supersaturated transition metals are not well understood.…”

Section: Introductionmentioning

confidence: 99%

The relaxation behaviour of supersaturated iron in single-crystal silicon at 500 to 750 °C

Murphy¹,

Falster²

2012

Journal of Applied Physics

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Section: Introductionmentioning

confidence: 99%

The relaxation behaviour of supersaturated iron in single-crystal silicon at 500 to 750 °C

Murphy¹,

Falster²

2012

Journal of Applied Physics

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“…Processes such as phosphorus diffusion gettering and aluminium gettering rely on higher impurity solubility in the gettering layer compared to in the silicon 7. Another approach is to use long low temperature (∼500 to 700 °C) anneals to redistribute impurities to regions where they are less detrimental to minority carrier lifetime 8, 9. This requires a delicate balance between low solubility (to prevent further contamination) and sufficiently high diffusivity, and studies have shown improvements in lifetime 8 and cell efficiency 9.…”

Section: Introductionmentioning

confidence: 99%

“…Another approach is to use long low temperature (∼500 to 700 °C) anneals to redistribute impurities to regions where they are less detrimental to minority carrier lifetime 8, 9. This requires a delicate balance between low solubility (to prevent further contamination) and sufficiently high diffusivity, and studies have shown improvements in lifetime 8 and cell efficiency 9. To improve both these gettering methods it is first necessary to know the solubility of iron in silicon itself.…”

Section: Introductionmentioning

confidence: 99%

“…However, processes are often performed at temperatures below 800 °C. As well as the long low temperature gettering anneals 8, 9, annealing at ∼650 °C is routinely used in IC silicon to annihilate thermal donor defects 11. It is therefore vital to understand how much iron can dissolve in silicon at these lower temperatures too, and this is the subject of this Letter.…”

Section: Introductionmentioning

confidence: 99%

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Contamination of silicon by iron at temperatures below 800 °C

Murphy

Falster

2011

Physica Rapid Research Ltrs

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Iron‐related defects are deleterious in silicon‐based integrated circuits and photovoltaics, ruining devices and acting as strong recombination centres. Unless great care is taken, iron contamination will result from high temperature processing and so it is essential to understand the degree to which this can occur. Iron solubility data above ∼800 °C have been summarised by Istratov et al. (Appl. Phys. A 69, 13 (1999)), but many processes are performed at lower temperatures for which solubility data are scarce. We have studied iron contamination below ∼800 °C. Iron concentrations in intention‐ ally contaminated air‐annealed Czochralski silicon samples were determined from the change in minority carrier lifetime due to photodissociation of FeB pairs measured by quasi‐steady‐state photoconductance. In the ∼600 to 800 °C temperature range the iron concentration was found to vary according to $ 1.3 \times 10^{21} \; {\rm exp} \;\left (‐ { {1.8\;{\rm eV} } \over {kT} } \right)\;{\rm cm}^{‐3}. It is therefore the case that significantly more iron can dissolve in silicon at these temperatures than extrapolation of higher temperature data suggests, with the enhancement being by a factor of >20 at 600 °C. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…Although this potentially requires longer annealing times, the advantage is that the solubility of many impurities is low and so in principle the processing can be performed under non-cleanroom conditions. We note that long low temperature annealing has been demonstrated to improve lifetime in mono-Si [8,9]. For mono-Si the gettering probably occurs externally at surfaces [8,10], whereas in mc-Si it is likely that long low temperature annealing will result in internal gettering.…”

Section: Introductionmentioning

confidence: 93%

Low Temperature Internal Gettering of Bulk Defects in Silicon Photovoltaic Materials

Al‐Amin

Murphy

2015

SSP

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Abstract. Multicrystalline silicon (mc-Si) substrates are widely used for photovoltaic cells. The minority carrier lifetime in mc-Si is affected by recombination associated with metallic impurities in many forms, such as point-like defects, precipitates and bound to or precipitated at structural defects such as dislocations. We have studied the effect of low temperature annealing on the lifetime and bulk iron concentration in as-received mc-Si wafers from different locations within a block. Lifetime measurements are made using a temporary iodine-ethanol surface passivation technique to minimize the occurrence of bulk hydrogenation which often occurs from dielectric films. In good wafers from the middle of the block the lifetime is reduced by annealing at 400 °C and 500 °C in a way which does not correlate with changes in bulk iron concentration. Lifetime improvements occur in relatively poor samples from the top and bottom of the block annealed at 300 °C, and also in samples from the bottom annealed at 400 °C. The improvement in bottom wafers correlates with iron loss from the bulk. Our work shows that under some conditions the lifetime in relatively poor as-grown wafers can be improved by low temperature internal gettering.

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Cathodoluminescence assessment of annealed silicon and a novel technique for estimating minority carrier lifetime in silicon

Cited by 6 publications

References 8 publications

The relaxation behaviour of supersaturated iron in single-crystal silicon at 500 to 750 °C

The relaxation behaviour of supersaturated iron in single-crystal silicon at 500 to 750 °C

Contamination of silicon by iron at temperatures below 800 °C

Low Temperature Internal Gettering of Bulk Defects in Silicon Photovoltaic Materials

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