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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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Related in: MedlinePlus

O 1 s XPS spectra of Al2O3films. Films were deposited by T-ALD (a) and by PE-ALD (b). The solid black lines represent the fitted curves.
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Fig4: O 1 s XPS spectra of Al2O3films. Films were deposited by T-ALD (a) and by PE-ALD (b). The solid black lines represent the fitted curves.

Mentions: Figure 4a,b show the O 1 s core level spectra of Al2O3 films deposited by PE-ALD and T-ALD before and after annealing. Two components are de-convoluted form O 1 s peak - one centered at approximately 531.8 eV corresponding to Al-OH of AlOOH or Al(OH)3 and the other centered at approximately 530.7 eV corresponding to O-Al-O bonds of Al2O3. The fitted component curves (Al2O3, red line) in Figure 4b show that O-Al-O bonds have a higher occupation area than Al-OH bonds (Al-OH, blue line) in the PE-ALD-deposited film, and the area ratio (AAl2O3/AAl-OH) increases from 3:2 to 3:1 after annealing. By contrast with PE-ALD film, the area ratio of the T-ALD-deposited film is lower. But the variation trends of PE-ALD- and T-ALD-deposited films are similar after annealing, and the area ratio of the T-ALD film also increases from 3:7 to 5:4, showed in Figure 4a. The increase of the T-ALD area ratio after annealing is attributed to the residual O-H bonds breaking at high temperature. The bond breaking releases the interstitial H atoms which diffuse into the Al2O3 film and the Al2O3/Si interface [21], and saturate the dangling bonds of the silicon surface as discussed above. Simultaneously, the residual O-H bond breaking also releases Al atoms to form more O-Al-O bonds of Al2O3. By contrast with the PE-ALD film, the lower area ratio of the T-ALD film indicates that the reaction activity of H2O is lower than that of plasma O and residual OH group absorbed during reaction between TMA and H2O. In another aspect, the relatively stable area ratios for PE-ALD film before and after annealing are due to the high reaction activity of plasma O, which allows for a higher reaction ratio with TMA.Figure 4


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)

O 1 s XPS spectra of Al2O3films. Films were deposited by T-ALD (a) and by PE-ALD (b). The solid black lines represent the fitted curves.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig4: O 1 s XPS spectra of Al2O3films. Films were deposited by T-ALD (a) and by PE-ALD (b). The solid black lines represent the fitted curves.
Mentions: Figure 4a,b show the O 1 s core level spectra of Al2O3 films deposited by PE-ALD and T-ALD before and after annealing. Two components are de-convoluted form O 1 s peak - one centered at approximately 531.8 eV corresponding to Al-OH of AlOOH or Al(OH)3 and the other centered at approximately 530.7 eV corresponding to O-Al-O bonds of Al2O3. The fitted component curves (Al2O3, red line) in Figure 4b show that O-Al-O bonds have a higher occupation area than Al-OH bonds (Al-OH, blue line) in the PE-ALD-deposited film, and the area ratio (AAl2O3/AAl-OH) increases from 3:2 to 3:1 after annealing. By contrast with PE-ALD film, the area ratio of the T-ALD-deposited film is lower. But the variation trends of PE-ALD- and T-ALD-deposited films are similar after annealing, and the area ratio of the T-ALD film also increases from 3:7 to 5:4, showed in Figure 4a. The increase of the T-ALD area ratio after annealing is attributed to the residual O-H bonds breaking at high temperature. The bond breaking releases the interstitial H atoms which diffuse into the Al2O3 film and the Al2O3/Si interface [21], and saturate the dangling bonds of the silicon surface as discussed above. Simultaneously, the residual O-H bond breaking also releases Al atoms to form more O-Al-O bonds of Al2O3. By contrast with the PE-ALD film, the lower area ratio of the T-ALD film indicates that the reaction activity of H2O is lower than that of plasma O and residual OH group absorbed during reaction between TMA and H2O. In another aspect, the relatively stable area ratios for PE-ALD film before and after annealing are due to the high reaction activity of plasma O, which allows for a higher reaction ratio with TMA.Figure 4

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