Hydrogenation Mechanisms of Poly‐Si/SiO<sub><i>x</i></sub> Passivating Contacts by Different Capping Layers

Truong, Thien N.; Yan, Donghang; Chen, Wen‐Hao; Tebyetekerwa, Mike; Young, Matthew R.; Al‐Jassim, Mowafak; Cuevas, Andrés; Macdonald, Daniel; Nguyen, Hieu T.

doi:10.1002/solr.201900476

Cited by 15 publications

(18 citation statements)

References 34 publications

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“…Those findings, together with the fact that the samples, were previously exposed to a much longer high‐temperature step where most of the hydrogen should already have diffused out and only few SiH bonds should be present 32,44,46 support the hypothesis that here, mainly another defect formation process is taking place than the out‐diffusion of hydrogen.…”

Section: Discussionsupporting

confidence: 61%

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

Hollemann

Rienäcker

Soeriyadi

et al. 2021

Progress in Photovoltaics

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Stability of the passivation quality of poly-Si on oxide junctions against the conventional mainstream high-temperature screen-print firing processes is highly desirable and also expected since the poly-Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J 0 ) and interface state densities (D it ) of symmetrical samples with n-type poly-Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The D it values are (3 ± 0.2) Â 10 11 and (8 ± 2) Â 10 11 eV/cm 2 when fired at 620 C and 900 C, respectively. The activation energy in an Arrhenius fit of D it versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from Si H bonds at the poly-Si/SiO x interface is not the root cause of depassivation. Postfiring annealing at 425 C can improve the passivation again. Samples with SiN x capping layers show an increase in J 0 up to about 100 fA/cm 2 by firing, which can be attributed to blistering and is not reversed by annealing at 425 C. On the other hand, blistering does not occur in poly-Si samples capped with AlO x layers or AlO x /SiN y stacks, and J 0 values of 2-5 fA/cm 2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J 0 and D it : thermal stress at the SiO z interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.

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Section: Discussionsupporting

confidence: 61%

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

Hollemann

Rienäcker

Soeriyadi

et al. 2021

Progress in Photovoltaics

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“…Something similarly has been reported for a-Si:H(p) and a-Si:H(n) in silicon heterojunction (SHJ) interfaces [61]. In the SHJ structure, hydrogen effusion is more energetically favorable for p-type a-Si:H, when E F is close to the valence band, which induces lower thermal stability in comparison to n-type a-Si:H. For the hydrogenated p + poly-Si samples, it still needs to be clarified whether the observed lower thermal stability for p + poly-Si samples compared to n + poly-Si samples can be attributed to similar reasons [26], [27], [42], [62], [63]. Obviously, the overall passivation quality provided by the Al 2 O 3 /SiN x double capping layer approach is not significantly better than the Al 2 O 3 single-layer approach for p + poly-Si.…”

Section: Discussionmentioning

confidence: 99%

Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al₂O₃ Capping Layers

Yang

Loo

Stodolny

et al. 2022

IEEE J. Photovoltaics

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Hydrogenation of polycrystalline silicon (poly-Si) passivating contacts is crucial for maximizing their passivation performance. This work presents the application of Al 2 O 3 prepared by atomic layer deposition as a hydrogenating capping layer. Several important questions related to this application of Al 2 O 3 are addressed by comparing results from Al 2 O 3 single layers, SiN x single layers, and Al 2 O 3 /SiN x double layers to different poly-Si types. We investigate the effect of the Al 2 O 3 thickness, the poly-Si thickness, the poly-Si doping type, and the postdeposition annealing treatment on the passivation quality of poly-Si passivating contacts. Especially, the Al 2 O 3 /SiN x stack greatly enhances the passivation quality of both n + and p + doped as well as intrinsic poly-Si layers. The Al 2 O 3 layer thickness is crucial for the single-layer approach, whereas the Al 2 O 3 /SiN x stack is less sensitive to the thickness of the Al 2 O 3 layer. A thicker Al 2 O 3 layer is needed for effectively hydrogenating p + compared to n + poly-Si passivating contact. The capping layers can hydrogenate poly-Si layers with thicknesses up to at least 600 nm. The hydrogenation-enhanced passivation for n + poly-Si is found to be more thermally stable in comparison to p + poly-Si. These results provide guidelines on the use of Al 2 O 3 capping layers for poly-Si contacts to significantly improve their passivation performance. Index Terms-Atomic layer deposition (ALD) Al 2 O 3 , hydrogenation, passivation quality, polycrystalline silicon (poly-Si) passivating contacts, thermal stability. I. INTRODUCTIONC RYSTALLINE silicon (c-Si) solar cells with polycrystalline silicon (poly-Si) as passivating contacts enable Manuscript

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“…Therefore, the deposited Si films are partially recrystallized, and the hydrogen that may have been incorporated inside the films has effused out during the deposition. 38 However, regardless of whether the hydrogen is present in the as-deposited films or not, after the required high-temperature ex situ diffusion step (>800 C), the subsequent passivating contacts show no trace of hydrogen in the captured PL spectra (i.e., no a-Si:H peak) for all the deposition methods (Figure 2D-F). The PL spectra show clear c-Si substrate peaks ($1125 nm) and broad radiative defect peaks from poly-Si layers ($1200-1500 nm) for all samples.…”

Section: Luminescence Properties and Hydrogen Contentmentioning

confidence: 99%

“…Also, the iV oc results may be improved by the use of hydrogenation techniques such as depositing hydrogenated silicon nitride (SiN x :H) or hydrogenated aluminium oxide (AlO x :H) capping layers and annealing in forming gas (FGA). 34,38,[46][47][48] The passivation quality of the poly-Si/SiO x stacks depends strongly on the poly-Si film properties. Each film has its unique response to the diffusion step, as shown in previous sections.…”

Section: Surface Morphologiesmentioning

confidence: 99%

Morphology, microstructure, and doping behaviour: A comparison between different deposition methods for poly‐Si/SiO_x passivating contacts

Truong

Yan

Nguyen

et al. 2021

Progress in Photovoltaics

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Crystallographic structures, optoelectronic properties, and nanoscale surface morphologies of ex situ phosphorus-doped polycrystalline silicon (poly-Si)/SiO x passivating contacts, formed by different deposition methods (sputtering, plasmaenhanced chemical vapour deposition [PECVD], and low-pressure chemical vapour deposition [LPCVD]), are investigated and compared. Across all these deposition technologies, we noted the same trend: higher diffusion temperatures yield films that are more crystalline but that have rougher surface morphologies due to bigger surface crystal grains. Also, the recrystallization process of the as-deposited Si films starts from the SiO x interface, rather than from the film surface and bulk. However, there are some distinct differences among these technologies. First, the LPCVD method yields the lowest deposition rate, roughest surfaces, and smallest degree of crystallinity on finished poly-Si films. In contrast, the PECVD method has the highest deposition rate and smoothest surfaces for both as-deposited Si and annealed poly-Si films. Second, as-deposited sputtered and PECVD Si films contain only an amorphous phase, whereas as-deposited LPCVD films already has some crystalline phase. Third, the LPCVD phosphorus in-diffusion into the substrate depends strongly on the initial film thickness, whereas for the other two methods, it is weakly dependent on thickness. Finally, the passivation quality of every poly-Si film type has different responses to the film thickness and diffusion temperature, suggesting that the ex situ doping optimization should be performed independently.

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Hydrogenation Mechanisms of Poly‐Si/SiO_x Passivating Contacts by Different Capping Layers

Cited by 15 publications

References 34 publications

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al₂O₃ Capping Layers

Morphology, microstructure, and doping behaviour: A comparison between different deposition methods for poly‐Si/SiO_x passivating contacts

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Hydrogenation Mechanisms of Poly‐Si/SiOx Passivating Contacts by Different Capping Layers

Cited by 15 publications

References 34 publications

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al2O3 Capping Layers

Morphology, microstructure, and doping behaviour: A comparison between different deposition methods for poly‐Si/SiOx passivating contacts

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Hydrogenation Mechanisms of Poly‐Si/SiO_x Passivating Contacts by Different Capping Layers

Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al₂O₃ Capping Layers

Morphology, microstructure, and doping behaviour: A comparison between different deposition methods for poly‐Si/SiO_x passivating contacts