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Oxidation precursor dependence of atomic layer deposited Al2O3 films in a-Si:H(i)/Al2O3 surface passivation stacks.

Xiang Y, Zhou C, Jia E, Wang W - Nanoscale Res Lett (2015)

Bottom Line: For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used.Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives.In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, No. 6 Beiertiao, Zhongguancun, Beijing, 100190 China.

ABSTRACT
In order to obtain a good passivation of a silicon surface, more and more stack passivation schemes have been used in high-efficiency silicon solar cell fabrication. In this work, we prepared a-Si:H(i)/Al2O3 stacks on KOH solution-polished n-type solar grade mono-silicon(100) wafers. For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used. Interface trap density spectra were obtained for Si passivation with a-Si films and a-Si:H(i)/Al2O3 stacks by a non-contact corona C-V technique. After the fabrication of a-Si:H(i)/Al2O3 stacks, the minimum interface trap density was reduced from original 3 × 10(12) to 1 × 10(12) cm(-2) eV(-1), the surface total charge density increased by nearly one order of magnitude for PE-ALD samples and about 0.4 × 10(12) cm(-2) for a T-ALD sample, and the carrier lifetimes increased by a factor of three (from about 10 μs to about 30 μs). Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives. In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

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Effective lifetime for n-type Si capped with Al2O3films before and after annealing. The thickness of Al2O3 films is about 20 nm and the annealing process is done at 450°C for 10 min in air. The substrate temperature (Sub-T) and the number of ALD cycles are also shown here.
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Fig2: Effective lifetime for n-type Si capped with Al2O3films before and after annealing. The thickness of Al2O3 films is about 20 nm and the annealing process is done at 450°C for 10 min in air. The substrate temperature (Sub-T) and the number of ALD cycles are also shown here.

Mentions: For the reference samples (Ф100 mm) covered by Al2O3 films on both sides, the effective minority carrier lifetimes before and after annealing are shown in Figure 2. The T-ALD samples have higher effective minority carrier lifetimes just before deposition, but the advantage is lost after annealing contrasted with PE-ALD samples, especially for the Al2O3 deposition at the low substrate temperature of 100°C. The samples with the high substrate temperature of 200°C for both deposition types show higher effective minority carrier lifetimes after annealing (1,647 μs for PE-ALD deposition, 1,232 μs for T-ALD deposition). The reasons for the different performances in the effective minority carrier lifetime for the two ALD deposition Al2O3 films are considered as follows: First, Dit of PE-ALD Al2O3 film-passivated Si surfaces is higher than that of T-ALD Al2O3 film-passivated Si surfaces due to the presence of vacuum ultraviolet radiation in the O2 plasma. Thus PE-ALD interfaces need an annealing step to improve performance. Second, the fixed charge densities in T-ALD Al2O3 films are lower than those in PE-ALD Al2O3 films [2]. The fixed charge density is related to field-effect passivation. The origin of the negative fixed charge in the Al2O3 film is considered to be related to the effect of the interfacial SiOx film which is formed during the ALD deposition [16].Figure 2


Oxidation precursor dependence of atomic layer deposited Al2O3 films in a-Si:H(i)/Al2O3 surface passivation stacks.

Xiang Y, Zhou C, Jia E, Wang W - Nanoscale Res Lett (2015)

Effective lifetime for n-type Si capped with Al2O3films before and after annealing. The thickness of Al2O3 films is about 20 nm and the annealing process is done at 450°C for 10 min in air. The substrate temperature (Sub-T) and the number of ALD cycles are also shown here.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385324&req=5

Fig2: Effective lifetime for n-type Si capped with Al2O3films before and after annealing. The thickness of Al2O3 films is about 20 nm and the annealing process is done at 450°C for 10 min in air. The substrate temperature (Sub-T) and the number of ALD cycles are also shown here.
Mentions: For the reference samples (Ф100 mm) covered by Al2O3 films on both sides, the effective minority carrier lifetimes before and after annealing are shown in Figure 2. The T-ALD samples have higher effective minority carrier lifetimes just before deposition, but the advantage is lost after annealing contrasted with PE-ALD samples, especially for the Al2O3 deposition at the low substrate temperature of 100°C. The samples with the high substrate temperature of 200°C for both deposition types show higher effective minority carrier lifetimes after annealing (1,647 μs for PE-ALD deposition, 1,232 μs for T-ALD deposition). The reasons for the different performances in the effective minority carrier lifetime for the two ALD deposition Al2O3 films are considered as follows: First, Dit of PE-ALD Al2O3 film-passivated Si surfaces is higher than that of T-ALD Al2O3 film-passivated Si surfaces due to the presence of vacuum ultraviolet radiation in the O2 plasma. Thus PE-ALD interfaces need an annealing step to improve performance. Second, the fixed charge densities in T-ALD Al2O3 films are lower than those in PE-ALD Al2O3 films [2]. The fixed charge density is related to field-effect passivation. The origin of the negative fixed charge in the Al2O3 film is considered to be related to the effect of the interfacial SiOx film which is formed during the ALD deposition [16].Figure 2

Bottom Line: For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used.Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives.In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Solar Thermal Energy and Photovoltaic System, Institute of Electrical Engineering, Chinese Academy of Sciences, No. 6 Beiertiao, Zhongguancun, Beijing, 100190 China.

ABSTRACT
In order to obtain a good passivation of a silicon surface, more and more stack passivation schemes have been used in high-efficiency silicon solar cell fabrication. In this work, we prepared a-Si:H(i)/Al2O3 stacks on KOH solution-polished n-type solar grade mono-silicon(100) wafers. For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used. Interface trap density spectra were obtained for Si passivation with a-Si films and a-Si:H(i)/Al2O3 stacks by a non-contact corona C-V technique. After the fabrication of a-Si:H(i)/Al2O3 stacks, the minimum interface trap density was reduced from original 3 × 10(12) to 1 × 10(12) cm(-2) eV(-1), the surface total charge density increased by nearly one order of magnitude for PE-ALD samples and about 0.4 × 10(12) cm(-2) for a T-ALD sample, and the carrier lifetimes increased by a factor of three (from about 10 μs to about 30 μs). Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives. In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

No MeSH data available.


Related in: MedlinePlus