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Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system.

Lien SY, Yang CH, Wu KC, Kung CY - Nanoscale Res Lett (2015)

Bottom Line: Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters.Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (V oc) and short-circuit current (J sc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively.The electrical performance of the optimized PERC with the V oc of 0.647 V, J sc of 38.2 mA/cm(2), fill factor of 0.776, and the efficiency of 19.18% can be achieved.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, DaYeh University, No. 168, Xuefu Road, Changhua, 515 Taiwan.

ABSTRACT
Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (V oc) and short-circuit current (J sc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the V oc of 0.647 V, J sc of 38.2 mA/cm(2), fill factor of 0.776, and the efficiency of 19.18% can be achieved.

No MeSH data available.


Related in: MedlinePlus

Injection level dependent minority carrier lifetime for the stacked passivation film. Si/3 nm-SiO2/8 nm-Al2O3/70 nm-SiNx:H film and Si/3 nm-SiO2/6 nm-Al2O3/70 nm-SiNx:H film.
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Fig6: Injection level dependent minority carrier lifetime for the stacked passivation film. Si/3 nm-SiO2/8 nm-Al2O3/70 nm-SiNx:H film and Si/3 nm-SiO2/6 nm-Al2O3/70 nm-SiNx:H film.

Mentions: For further improvement for the blistering problem, we reduce the thickness of Al2O3 to lower than 10 nm and increase the annealing temperature to 650°C, giving an enough thermal budget prior to the capping of the SiNx:H film. The out-gassing phenomenon can be found. Here, the blister number can further decrease, approaching near blister free. Some voids existing within the Al2O3 film are caused by the out-gassing effusion. However, the subsequent deposition of SiNx:H prepared by ICPCVD would provide abundant hydrogen atoms to fill the dangling bonds via the voids. The post-anneal (450°C for 20 min) performed after the deposition of SiNx:H is able to activate the passivation of the triple-layer stacked structure [19]. Figure 6 shows the injection level dependent minority carrier lifetime for the stacked passivation film of Si/3 nm-SiO2/8 nm-Al2O3/70 nm-SiNx:H film and of Si/3 nm-SiO2/6 nm-Al2O3/70 nm-SiNx:H film. The effective lifetime is calculated from the photoluminescence intensity by the self-consistent calibration method proposed by Trupke et al. [20]. Both the triple-layer stacked films have the same structure except the thickness of the Al2O3 film. The former one has a higher average lifetime of 315 μs compared to the latter one of 147 μs. Two major factors, negative fixed charge and blisters, are found to influence the lifetime of the Al2O3 films. Generally, reducing the thickness of the Al2O3 films to lower than 10 nm and increasing a post-annealing temperature to higher than 650°C can make blisters out-gassed. In this case, both 6- and 8-nm Al2O3 films are blister free, indicating the lifetime is determined only by negative fixed charge. According to our previous research and some references [21,22], the negative fixed charge may accumulate to enhance the passivation effect as the thickness increases. Hence, the sample with an 8-nm-thick Al2O3 layer has a higher lifetime, displaying stronger field-effect passivation than the sample with a 6-nm-thick Al2O3 layer. The optimized lifetime of 315 μs is about three times higher than 107.2 μs of the stacked film without SiNx:H. Note that the thickness of the Al2O3 within the triple-layer stacked film is reduced to lower than 10 nm, decreasing its field-effect passivation. However, according to some investigation of [23-26], they demonstrate that a thin Al2O3 of about 10 nm is still sufficient for providing an excellent level of surface passivation. Despite the field-effect passivation may become weaker in this case, the chemical passivation from SiNx:H dominates the whole performance strongly. For a short summary, hydrogen atom indeed plays a critical role in combing with the Al2O3 film as the passivation stacks.Figure 6


Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system.

Lien SY, Yang CH, Wu KC, Kung CY - Nanoscale Res Lett (2015)

Injection level dependent minority carrier lifetime for the stacked passivation film. Si/3 nm-SiO2/8 nm-Al2O3/70 nm-SiNx:H film and Si/3 nm-SiO2/6 nm-Al2O3/70 nm-SiNx:H film.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Fig6: Injection level dependent minority carrier lifetime for the stacked passivation film. Si/3 nm-SiO2/8 nm-Al2O3/70 nm-SiNx:H film and Si/3 nm-SiO2/6 nm-Al2O3/70 nm-SiNx:H film.
Mentions: For further improvement for the blistering problem, we reduce the thickness of Al2O3 to lower than 10 nm and increase the annealing temperature to 650°C, giving an enough thermal budget prior to the capping of the SiNx:H film. The out-gassing phenomenon can be found. Here, the blister number can further decrease, approaching near blister free. Some voids existing within the Al2O3 film are caused by the out-gassing effusion. However, the subsequent deposition of SiNx:H prepared by ICPCVD would provide abundant hydrogen atoms to fill the dangling bonds via the voids. The post-anneal (450°C for 20 min) performed after the deposition of SiNx:H is able to activate the passivation of the triple-layer stacked structure [19]. Figure 6 shows the injection level dependent minority carrier lifetime for the stacked passivation film of Si/3 nm-SiO2/8 nm-Al2O3/70 nm-SiNx:H film and of Si/3 nm-SiO2/6 nm-Al2O3/70 nm-SiNx:H film. The effective lifetime is calculated from the photoluminescence intensity by the self-consistent calibration method proposed by Trupke et al. [20]. Both the triple-layer stacked films have the same structure except the thickness of the Al2O3 film. The former one has a higher average lifetime of 315 μs compared to the latter one of 147 μs. Two major factors, negative fixed charge and blisters, are found to influence the lifetime of the Al2O3 films. Generally, reducing the thickness of the Al2O3 films to lower than 10 nm and increasing a post-annealing temperature to higher than 650°C can make blisters out-gassed. In this case, both 6- and 8-nm Al2O3 films are blister free, indicating the lifetime is determined only by negative fixed charge. According to our previous research and some references [21,22], the negative fixed charge may accumulate to enhance the passivation effect as the thickness increases. Hence, the sample with an 8-nm-thick Al2O3 layer has a higher lifetime, displaying stronger field-effect passivation than the sample with a 6-nm-thick Al2O3 layer. The optimized lifetime of 315 μs is about three times higher than 107.2 μs of the stacked film without SiNx:H. Note that the thickness of the Al2O3 within the triple-layer stacked film is reduced to lower than 10 nm, decreasing its field-effect passivation. However, according to some investigation of [23-26], they demonstrate that a thin Al2O3 of about 10 nm is still sufficient for providing an excellent level of surface passivation. Despite the field-effect passivation may become weaker in this case, the chemical passivation from SiNx:H dominates the whole performance strongly. For a short summary, hydrogen atom indeed plays a critical role in combing with the Al2O3 film as the passivation stacks.Figure 6

Bottom Line: Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters.Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (V oc) and short-circuit current (J sc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively.The electrical performance of the optimized PERC with the V oc of 0.647 V, J sc of 38.2 mA/cm(2), fill factor of 0.776, and the efficiency of 19.18% can be achieved.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, DaYeh University, No. 168, Xuefu Road, Changhua, 515 Taiwan.

ABSTRACT
Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (V oc) and short-circuit current (J sc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the V oc of 0.647 V, J sc of 38.2 mA/cm(2), fill factor of 0.776, and the efficiency of 19.18% can be achieved.

No MeSH data available.


Related in: MedlinePlus