Influence of Hydrogen on the Mechanism of Permanent Passivation of Boron–Oxygen Defects in p-Type Czochralski Silicon

Nampalli, Nitin; Hallam, Brett; Abbott, Malcolm; Wenham, Stuart

doi:10.1109/jphotov.2015.2466457

Cited by 29 publications

(21 citation statements)

References 17 publications

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“…The permanent recovery kinetics in low‐hydrogen samples (and in hydrogenated samples as well ) is well described by a simple exponential reduction in the room‐temperature reciprocal lifetime: 1/ τ = a + b exp(− R de t ) thus yielding a definite rate constant R de . An example , for anneal at 185 °C/1 sun is shown in Fig.…”

Section: Permanent Deactivation Modelmentioning

confidence: 99%

“…The first one deals with samples subjected to rapid thermal processing (RTP) at a relatively high T , such as 750 °C that imitates the contact firing in solar cell fabrication. These samples – if they have been coated with a hydrogen‐rich nitride prior to firing – tend to show a relatively fast deactivation by subsequent illuminated anneal.…”

Section: Introductionmentioning

confidence: 99%

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Permanent deactivation of boron-oxygen recombination centres in silicon

Voronkov

Falster

2016

Phys. Status Solidi B

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The major B–O recombination centres in p‐type silicon (labelled SRC) are known to be permanently deactivated at elevated temperature in the presence of excess electrons. This process is accelerated by hydrogen but it occurs also in low‐hydrogen material which is the main concern of the present article. A close inspection of the experimental data shows that: (i) the deactivation rate constant Rde is proportional to the electron concentration n and thus completely controlled by the electron lifetime τ and (ii) the value of τ at elevated T is insensitive to SRC; this is controlled by BO2 defects that reconstruct, in the presence of excess electrons, from the initial latent configuration into a recombination‐active one (FRC). This scenario accounts for the reported dependence of Rde on temperature, light intensity and the material parameters.

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Section: Permanent Deactivation Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Permanent deactivation of boron-oxygen recombination centres in silicon

Voronkov

Falster

2016

Phys. Status Solidi B

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“…In contrast to LeTID, an increase in peak firing temperature and cooling rate is known to decrease the magnitude of BO-LID, 33,34 which is opposite to the trend observed here. However, an increase in non-BO related LID has been observed in Cz silicon at peak firing temperatures above $650 C. 33,35 While such effects have been attributed to LeTID, 36,37 the possibility of Cu-LID being responsible for such LID effects has not been specifically precluded in such studies. It must be noted that there exist other empirical differences between LeTID and Cu-LID (e.g., SRH properties 29,38,39 and activation energy of degradation 31,38 ).…”

Section: à3mentioning

confidence: 99%

Rapid thermal anneal activates light induced degradation due to copper redistribution

Nampalli

Laine

Colwell

et al. 2018

Applied Physics Letters

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While it is well known that copper impurities can be relatively easily gettered from the silicon bulk to the phosphorus or boron–doped surface layers, it has remained unclear how thermally stable the gettering actually is. In this work, we show experimentally that a typical rapid thermal anneal (RTA, a few seconds at 800 °C) used commonly in the semiconductor and photovoltaic industries is sufficient to release a significant amount of Cu species from the phosphorus-doped layer to the wafer bulk. This is enough to activate the so-called copper-related light-induced degradation (Cu-LID) which results in significant minority carrier lifetime degradation. We also show that the occurrence of Cu-LID in the wafer bulk can be eliminated both by reducing the RTA peak temperature from 800 °C to 550 °C and by slowing the following cooling rate from 40–60 °C/s to 4 °C/min. The behavior is similar to what is reported for Light and Elevated Temperature degradation, indicating that the role of Cu cannot be ignored when studying other LID phenomena. Numeric simulations describing the phosphorus diffusion and the gettering process reproduce the experimental trends and elucidate the underlying physical mechanisms.

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“…One theory was proposed, suggesting that the fast cooling rates reduce the concentration of interstitial boron-oxygen pairs (B i -O 2 ) and increase the sinking efficiency of boron nano-precipitates, which then determines the rate constant for regeneration [80]. However, subsequent studies have confirmed the critical role of the presence of a hydrogen-containing dielectric layer during firing and that the firing process alone cannot lead to complete suppression of B-O defect formation, nor is it purely caused by exposure to plasma processing [87,122,123].…”

Section: Alternative Theory For Permanent Deactivation and Confusion mentioning

confidence: 99%

“…Higher defect formation rates enable the use of higher processing temperatures without sacrificing the effectiveness of LID mitigation [89,93]. The increased temperatures can lead to a further acceleration of the processes due to the exponential dependence of the reaction rates on processing temperature as well as the increase in carrier concentrations and lifetime at higher temperatures [133,135]. However, if an excessively high temperature is used, an incomplete regeneration will result [87].…”

Section: Role Of Defect Formationmentioning

confidence: 99%

Eliminating Light-Induced Degradation in Commercial p-Type Czochralski Silicon Solar Cells

et al. 2017

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This paper discusses developments in the mitigation of light-induced degradation caused by boron-oxygen defects in boron-doped Czochralski grown silicon. Particular attention is paid to the fabrication of industrial silicon solar cells with treatments for sensitive materials using illuminated annealing. It highlights the importance and desirability of using hydrogen-containing dielectric layers and a subsequent firing process to inject hydrogen throughout the bulk of the silicon solar cell and subsequent illuminated annealing processes for the formation of the boron-oxygen defects and simultaneously manipulate the charge states of hydrogen to enable defect passivation. For the photovoltaic industry with a current capacity of approximately 100 GW peak, the mitigation of boron-oxygen related light-induced degradation is a necessity to use cost-effective B-doped silicon while benefitting from the high-efficiency potential of new solar cell concepts.

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Influence of Hydrogen on the Mechanism of Permanent Passivation of Boron–Oxygen Defects in p-Type Czochralski Silicon

Cited by 29 publications

References 17 publications

Permanent deactivation of boron-oxygen recombination centres in silicon

Permanent deactivation of boron-oxygen recombination centres in silicon

Rapid thermal anneal activates light induced degradation due to copper redistribution

Eliminating Light-Induced Degradation in Commercial p-Type Czochralski Silicon Solar Cells

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