Main defect reactions behind phosphorus diffusion gettering of iron

Schön, Jonas; Vähänissi, Ville; Haarahiltunen, Antti; Schubert, Martin C.; Warta, Wilhelm; Savin, Hele

doi:10.1063/1.4904961

Cited by 16 publications

(19 citation statements)

References 29 publications

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“…and the references therein). A more recent model proposed by Schön et al was shown to explain a range of experimental results reported in the literature concerning the PDG of Fe . The dominant gettering mechanisms were attributed to the reactions of (a) Fe with oxygen complexes and (b) Fe with either electrically active or inactive P atoms .…”

Section: Resultsmentioning

confidence: 84%

“…As reported previously, an undoped polysilicon layer exhibits much weaker gettering effects, indicating the importance of heavy phosphorus doping on the gettering effectiveness . Phosphorus diffusion gettering (PDG) has been long known and applied in both microelectronics and photovoltaics, yet there are multiple explanations in the literature for the underlying physical mechanisms (see, e.g., refs and . and the references therein).…”

Section: Resultsmentioning

confidence: 92%

“…Heavy doping of the polysilicon layer by P atoms is confirmed by the SIMS [P] profile in Figure . It is interesting to note that the P concentration in the poly-Si layer is higher than the SIMS measured P concentrations in the c-Si surface regions for direct POCl 3 diffusion on c-Si wafers. − This may relate to the high density of grain boundaries in poly-Si, where dopant accumulation and precipitation take place. − The blocking effect of the interfacial SiO x on the diffusion of P atoms, and the thinner poly-Si layers compared to the doped c-Si surface regions (tens to a couple hundred of nanometers of poly-Si as compared to several hundred nanometers to a few micrometers in c-Si), may also contribute to a higher level of dopant supersaturation in the poly-Si layer.…”

Section: Resultsmentioning

confidence: 97%

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Direct Observation of the Impurity Gettering Layers in Polysilicon-Based Passivating Contacts for Silicon Solar Cells

Liu

Yan

Wong‐Leung

et al. 2018

ACS Appl. Energy Mater.

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The formation of certain types of doped polysilicon passivating contacts for silicon solar cells is recently reported to generate very strong impurity gettering effects, revealing an important additional benefit of this passivating contact structure. This work investigates the underlying gettering mechanisms by directly monitoring the impurity redistribution during the contact formation and subsequent processes, via a combination of secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), and minority carrier lifetime techniques. Microscopic features of the phosphorus and boron diffusion-doped polysilicon passivating contacts are also presented. Iron is used as a marker impurity in silicon to enable direct quantification of its concentration change in the bulk of the silicon wafers and in the surface layers that compose the contact structure. The results conclusively show that, for phosphorus-doped polysilicon passivating contacts, impurities are relocated from the silicon wafer bulk to the heavily phosphorus-doped polysilicon layer; while for the boron diffusion-doped polysilicon, the boron-rich layer (a silicon−boron compound) accounts for the majority of the gettering action.

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Section: Resultsmentioning

confidence: 84%

Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 97%

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Direct Observation of the Impurity Gettering Layers in Polysilicon-Based Passivating Contacts for Silicon Solar Cells

Liu

Yan

Wong‐Leung

et al. 2018

ACS Appl. Energy Mater.

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“…The POCl 3 diffusion process included a drive-in step at 780 C for 15 min. It was well established that phosphorus diffusion allowed efficient impurity gettering over a wide range of process conditions due to a high segregation coefficient for iron between the bulk silicon and a P-diffused layer, [8] which can be further enhanced using immobile oxygen complexes [19] and inactive dopants. [20] On the other hand, to achieve both comparable gettering levels and good emitter properties appeared challenging for boron diffusion.…”

Section: Methodsmentioning

confidence: 99%

Impurity Gettering by Boron‐ and Phosphorus‐Doped Polysilicon Passivating Contacts for High‐Efficiency Multicrystalline Silicon Solar Cells

Hayes

Martel

Alam

et al. 2019

Physica Status Solidi (a)

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Highly doped polysilicon (poly-Si) on ultra-thin oxide layers are highlighted as they allow both carrier collection efficiency with a low contact resistivity and an excellent surface passivation. Their integration at the rear surface of a highquality single-crystalline silicon solar cell allows to achieve a record conversion efficiency of 25.7% for a double-side contacted device. However, so far, only a very few studies investigate the interactions between poly-Si passivating contacts and low-quality cheaper silicon wafers. Thus, this study focuses on the external gettering response of both boron (B) and phosphorus (P) in situ doped poly-Si passivating contacts on high-performance multicrystalline silicon. Wafers are extracted from five ingot heights and experience P-and B-doped poly-Si passivating contact fabrication processes. Subsequently, the bulk carrier lifetime and interstitial iron (Fe i ) concentration are characterized and compared with conventional POCl 3 and BCl 3 thermal diffusion steps, and as-cut references. The P-doped poly-Si contact fabrication process results in gettering more than 99% of the Fe i , which leads to an increase in the bulk carrier lifetime. Interestingly, the B-doped poly-Si contact also develops a substantial external gettering action, and allows removing 96% of the Fe i from the bulk.

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“…For the case of iron with phosphorus-diffused emitters, the segregation effect appears to be caused by reactions involving vacancies [8]- [10], oxygen [11], [12], and inactive phosphorus [13], [14]. An implanted emitter typically contains less inactive phosphorus [15] and, with the avoidance of a phosphosilicate glass, possibly less vacancies and oxygen as well [12]. Ion implantation may also cause parasitic metal contamination in and of itself [16].…”

Section: Introductionmentioning

confidence: 99%

Impact of Iron Precipitation on Phosphorus-Implanted Silicon Solar Cells

Laine

Vähänissi

Morishige

et al. 2016

IEEE J. Photovoltaics

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Ion implantation is a promising method to implement a high-performance emitter for crystalline silicon solar cells. However, an implanted emitter redistributes and mitigates harmful metal impurities to a different degree than a diffused one. This paper quantitatively assesses the effect of iron contamination level on the bulk diffusion length and open-circuit voltage of phosphorus-implanted solar cells manufactured with varying gettering parameters. By synchrotron-based micro-X-ray fluorescence measurements, we directly observe a process-dependent iron precipitate size distribution in the implanted emitters. We show that controlling the iron precipitate size distribution is important when optimizing final cell performance and discover a tradeoff between large shunting precipitates in the emitter and a high density of recombination active small precipitates in the wafer bulk. We present a heterogeneous iron precipitation model capable of reproducing the experimentally measured size distributions. We use the model to show that the dominant gettering mechanism in our samples is precipitation and that implanted emitters with surface phosphorus concentrations around 2×10 19 cm −3 induce little-tono segregation-based gettering. Based on this finding, we discuss optimal gettering strategies for industrial silicon solar cells with implanted emitters.

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Main defect reactions behind phosphorus diffusion gettering of iron

Cited by 16 publications

References 29 publications

Direct Observation of the Impurity Gettering Layers in Polysilicon-Based Passivating Contacts for Silicon Solar Cells

Direct Observation of the Impurity Gettering Layers in Polysilicon-Based Passivating Contacts for Silicon Solar Cells

Impurity Gettering by Boron‐ and Phosphorus‐Doped Polysilicon Passivating Contacts for High‐Efficiency Multicrystalline Silicon Solar Cells

Impact of Iron Precipitation on Phosphorus-Implanted Silicon Solar Cells

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