Issue
Eur. Phys. J. Appl. Phys.
Volume 89, Number 1, January 2020
Disordered Semiconductors: Physics and Applications
Article Number 10101
Number of page(s) 6
Section Semiconductors and Devices
DOI https://doi.org/10.1051/epjap/2020190299
Published online 27 March 2020

© EDP Sciences, 2020

1 Introduction

Decreasing the thickness of silicon (Si) wafer is an effective way to reduce material cost in crystalline Si (c-Si) solar cells, including Si heterojunction (SHJ) solar cells. Moreover, it is known to increase the open-circuit voltage of a solar cell [1], which is also advantageous. However, for a solar cell using a thinner Si wafer, higher-quality of surface passivation is required [2], other than advanced light trapping. Among materials for Si surface passivation layer, hydrogenated amorphous Si (a-Si:H) employed in SHJ solar cells has been recognized as an excellent material [3,4].

In this study, aiming to develop further Si surface passivation technique, we fabricated a-Si:H passivation layers on the surfaces of Si wafers by using triode-type plasma-enhanced chemical vapor deposition (PECVD) with gas-heating system [5], and discussed high-quality surface passivation for SHJ solar cells. The main features of the a-Si:H deposition technique are (1) selective transport of SiH3 radicals, favorable film-precursors, to substrate, (2) plasma damage-free, and (3) gas-heating effect. The first and the second features are realised by triode technique [6]. In the triode system, separation of plasma away from substrate is realized by means of a mesh electrode inserted between cathode and anode. This enables to eliminate species with short diffusion-length in SiH4 plasma, and then, SiH3 radicals with long diffusion-length both in SiH4 plasma and on the film-growing surface can be selectively transported to substrate. It is expected to be effective for high-quality a-Si:H deposition conformally on textured surfaces [7,8].

Concerning the third feature, the effects of gas-heating were demonstrated by the results of previous studies [5,9]: dangling-bond defect density of a-Si:H films grown at low substrate temperature (Tsub) can be reduced with gas-heating, while hydrogen content (CH) and bandgap (Eg) depend on Tsub, not on gas-heating, under conditions with a fixed Tsub. For Si surface passivation by using a-Si:H, epitaxial growth at a-Si:H/c-Si interface that occurs usually at a relatively high Tsub is known to be harmful [10,11]. That is why low Tsub-deposition of a-Si:H is advantageous to prevent the epitaxial growth. However, low Tsub-grown a-Si:H is generally very defective [12]. Then, to obtain high-quality a-Si:H passivation layers at a low Tsub, we focused on utilizing the triode-type PECVD technique with gas-heating.

2 Experimental

Intrinsic (i) a-Si:H passivation layers with a thickness of 6 or 12 nm were prepared on both sides of Si wafers by using our triode-type PECVD reactor with gas-heating system, shown in Figure 1. A novel configuration has been applied to gas-heating system in our reactor: a stainless steel wire mesh heated by Joule effect was placed outside of plasma generation area in order to minimize influence on plasma generation, whereas in the previous study [5], the triode mesh was Joule-heated. Thus, commonly used conditions for high-quality a-Si:H deposition are applicable in our system.

The structure of the samples was as follows: i a-Si:H (6 or 12 nm thick)/n-type c-Si (280 µm)/i a-Si:H (6 or 12 nm thick). Si wafers (float-zone (FZ), n-type (phosphorus-doped), <100>-oriented, ∼3.0 Ω cm, double-side-polished) with a thickness of 280 μm have been employed in this study. They were dipped in hydrofluoric acid (HF) solution (2%) for 60 s to remove the native oxide before the deposition of an a-Si:H passivation layer on both sides. The just HF-dipped Si wafer was immediately transferred to the load-lock of the PECVD system.

a-Si:H passivation layers were deposited by very-high-frequency (VHF)-PECVD with a frequency of 60 MHz. VHF power density was 30 mW/cm2. This was the minimal power density to maintain stable plasma under our deposition conditions. Pure monosilane (SiH4) was used as a source gas. Process gas pressure was 11 Pa. The distance between the cathode and the triode mesh was ∼20 mm, and that between the heated mesh and the substrate was fixed at ∼65 mm. The temperature of the heated mesh (Tmesh) measured by pyrometer was varied from 340 to 400 °C, and the temperature of the holder of substrate holder (Tholder) was kept at ∼100 °C. Note that the sensitivity of the thermometer was high for gas-heating, but low for heater-heating from below substrate holder, because of the positioning of the sensor. Therefore, it is probable that real substrate temperature (Tsub) was different from the measured Tholder, and that the difference would depend on conditions, e.g. Tmesh and distance between the mesh and the substrate.

After the deposition of an a-Si:H passivation layer on both sides, samples were annealed consecutively in forming gas (3% H2 in N2) atmosphere for 5 min at annealing temperatures (Tann) ranging from 200 to 250, 300 or 350 °C. (Exceptionally for the sample with 6 nm thick a-Si:H layers prepared with a Tmesh = 400 °C, post-deposition annealing at 350 °C was performed for 1 min as a test.)

Just after each annealing, the minority carrier effective lifetime (τeff) value of the samples was measured by quasi-steady-state photo-conductance (QSSPC) method [13] with Sinton Consulting WCT-120TS system, and the effective surface recombination velocity (S) of the samples was estimated to evaluate the surface passivation quality by [14]:(1)where τbulk and W are the bulk lifetime and wafer thickness, respectively. Here, τbulk was 8.8 ms for all the samples, and the minority carrier density for calculating the τeff and S was 1.0 × 1015 cm−3.

Spectroscopic ellipsometry was employed to determine the thickness and the bandgap (Eg) of the a-Si:H passivation layers. For observation of a-Si:H/c-Si interface and a-Si:H nanostructure, a high-resolution cross-sectional transmission electron microscopy (TEM) micrograph was acquired by a HITACHI High-Technologies H-9500 system with an acceleration voltage of 200 kV. The Si-hydrogen (H) bonding was investigated by Fourier-transform infrared spectroscopy (FT-IR) for ∼12 nm thick a-Si:H passivation layers deposited on both sides of a Si wafer. The H contents, CH SiH, CH SiH2, and CH SiH3, of the a-Si:H were determined from the integrated intensities of Si–H stretching-mode FT-IR absorption signals which were decomposed into three Gaussian distribution functions at around 2000 cm−1, 2080 cm−1, and 2140 cm−1, due to Si–H, Si=H2, and Si≡H3 bonds in a-Si:H, respectively. The total bonded H content (CH) was taken as the sum of CH SiH, CH SiH2, and CH SiH3. The proportionality constants used in this study were 9.0 × 1019 cm−2 for Si-H in a-Si:H and 2.2 × 1020 cm−2 for Si=H2 and Si≡H3 in a-Si:H [15].

The temperature-dependence of the τeff was also measured using a QSSPC system equipped with a substrate heater (Sinton Consulting WCT-120TS), for two samples with ∼12 nm thick a-Si:H passivation layers. The samples had been annealed at 250 °C, then air-exposed for a while, and annealed again at 250 °C before the measurements of the temperature-dependence of the τeff. The measurement temperatures ranged from 60 to 180 °C and measurements were carried out in air. The τeff was measured from a high temperature to minimize the effect of heat history of the c-Si wafer. The experimental details for the temperature-dependence of the τeff measurement are written elsewhere [16].

thumbnail Fig. 1

Our triode-type PECVD reactor with gas-heating system.

3 Results and discussion

3.1 Passivation quality and structural properties of the a-Si:H passivation layers

The total bonded H content (CH) and the proportion of (CH SiH2 + CH SiH3) in CH, (CH SiH2 + CH SiH3)/CH, are shown in Figure 2 as a function of Tmesh, where the CH SiH2 and the CH SiH3 are H contents in Si=H2 and Si≡H3 bonds, respectively, for as-deposited or 250 °C-annealed samples with ∼12 nm thick a-Si:H passivation layers. The data for an as-deposited sample with ∼8 nm thick a-Si:H layers prepared without gas-heating is also shown on the left side of the figure. The CH increases with increasing Tmesh from 340 to 400 °C. It was reported that the CH depends on Tsub, not on gas-heating [5]. Hence, the reason for the increase in CH with Tmesh is most probably that real Tsub would decrease with increasing Tmesh, even though the Tholder was fixed at 100 °C for all the samples. Real Tsub for the sample prepared without gas-heating would be the highest. It should be owing to bad positioning of the thermo-sensor, as mentioned in Section 2.

The surface recombination velocity (S) for samples with 6 or 12 nm thick a-Si:H passivation layers prepared with different Tmesh is shown in Figure 3 as a function of post-deposition annealing temperature (Tann). The S for as-deposited samples which is plotted tentatively at a Tann of 20 °C increases with Tmesh. This would reflect a decrease in real Tsub with increasing Tmesh. For the samples with 6 or 12 nm thick a-Si:H layers prepared with gas-heating, the S was very high before post-deposition annealing, and then decreased exponentially with increasing Tann to 300 °C. The maximum Tann for the samples with 12 nm thick a-Si:H layers prepared with a Tmesh of 340 or 370 °C was 250 °C, thus the S might be reduced further if they had been annealed at 300 °C. On the other hand, for the sample with ∼8 nm thick a-Si:H layers prepared without gas-heating, the S before annealing was lower than that obtained for the samples with a-Si:H layers prepared with gas-heating, and decreased exponentially with a looser slope when increasing the Tann to 250 °C. The relation between the S and the Tann for the samples prepared with or without gas-heating, or rather with different real Tsub is in accordance with the results reported previously for samples prepared with different Tsub [11].

As a result, relatively low S values of 1.15 and 2.64 cm/s have been obtained for the samples with 12 and 6 nm thick a-Si:H layers, respectively, prepared with a Tmesh of 370 °C. This Tmesh coincides with the Tmesh corresponding to the maximum (CH SiH2 + CH SiH3)/CH in Figure 2. This is consistent with the previous studies [17,18] which argue that use of underdense i a-Si:H with high CH SiH2/CH SiH ratio as a passivation layer is advantageous, because a highly disordered microstructure of the material inhibits an undesirable epitaxial growth at the a-Si:H/c-Si interface. Figure 4 shows TEM cross-sectional image for the sample with ∼12 nm thick a-Si:H layers prepared with a Tmesh of 370 °C which gave the minimum S of 1.15 cm/s after post-deposition annealing at 250 °C. No epitaxial growth is likely to be observed in the image.

It is well known that CH SiH2, CH SiH3, and CH as well as defect density increase with decreasing Tsub, for a-Si:H prepared at a Tsub below ∼250 °C [12,19] and that a-Si:H containing SiHx(x= 2,3) bonding is void-rich [20]. Such a low Tsub-grown a-Si:H ought to inhibit an epitaxial growth at the a-Si:H/c-Si interface, and then, structural relaxation of the a-Si:H is taking place during post-deposition annealing [11], leading to reduced defect density [19,21]. That results in high-quality surface passivation. The a-Si:H passivation layers of the sample corresponding to the maximum (CH SiH2 + CH SiH3)/CH and to the minimum S should be such a low Tsub-grown underdense material, and thus the importance to inhibit an epitaxial growth at the a-Si:H/c-Si interface is suggested in this study, as well.

Incidentally, the (CH SiH2 + CH SiH3)/CH is not the highest for the sample prepared with a Tmesh of 400 °C which would correspond to the lowest Tsub. This can be attributed to the effect of gas-heating [5,9]. Also, the triode technique is known to be effective for reducing the CH SiH2/CH [22]. That is to say, the technique employed in this study is not favorable to obtain a high (CH SiH2 +CH SiH3)/CH value. This might indicate that this technique can be utilized alternatively to form an a-Si:H bilayer passivation structure [18,23] consisting of an underdense interfacial layer and a denser overlaying layer: the interfacial layer prepared by conventional method or the triode technique, and the overlaying layer prepared using gas-heating and the triode technique. However, the relatively low S values obtained for our unoptimized samples imply the potency of this deposition technique for Si surface passivation using an a-Si:H single layer passivation structure. That should be owing to the effects of gas-heating and the triode technique.

Hence, for Si surface passivation using this deposition technique, inhibition of an epitaxial growth by using a low Tsub is necessary, and further, optimization of gas-heating and the triode technique together with the Tsub for obtaining simultaneously higher film quality and abrupt interface is important. For inhibition of an epitaxial growth, in addition, a very small fraction of H atoms reaching the film-growing surface, which is realized in the triode system due to the following gas phase reaction: SiH4 + H → SiH3 + H2, may be beneficial. Further optimization should improve the passivation quality by using this technique. Nevertheless, further studies, with precise monitoring and controlling of Tsub, are needed to elucidate the impact of gas-heating and the triode technique on Si surface passivation.

Note that the film growth rate depends on Tmesh or the electric current applied to the mesh (Imesh): it increases from 0.007 to 0.010 nm/s with increasing Imesh from 0 to 55 A. It is confirmed that there was no deposition without plasma generation, even with an Imesh of 55 A. The same tendency was also observed previously for samples deposited on glass substrates. In our system, the Joule-heated mesh possibly gives a positive bias effect to the triode mesh, and then, the plasma confined between the cathode and the triode mesh might become spread toward the heated mesh. Although the growth rate of ∼0.01 nm/s is low, this disadvantage is less serious compared to the case of a-Si:H thin film solar cells, because a very small thickness of approximately 4 nm is required for an a-Si:H passivation layer in order not to increase series resistance as well as parasitic light absorption. Still, higher growth rate will be preferred for industrial fabrication, and it should be realized by optimization of the process conditions.

thumbnail Fig. 2

Total bonded hydrogen content (CH) and (CH SiH2 +CH SiH3)/CH versus mesh temperature (Tmesh), where the CH SiH2 and the CH SiH3 are hydrogen contents in Si = H2 and Si≡H3, respectively, for as-deposited or 250 °C-annealed samples with ∼12 nm thick a-Si:H layers. The data for an as-deposited sample with ∼8 nm thick a-Si:H layers prepared without gas-heating is also shown on the left side of the figure.

thumbnail Fig. 3

Surface recombination velocity (S) versus post-deposition annealing temperature (Tann) for samples with 6 or 12 nm thick a-Si:H passivation layers prepared with different mesh temperature (Tmesh). Note that the thickness of the sample prepared without gas-heating was exceptionally ∼8 nm.

thumbnail Fig. 4

TEM cross-sectional image for the sample with ∼12 nm thick a-Si:H layers prepared with a mesh temperature (Tmesh) of 370 °C.

3.2 Temperature-dependence of minority carrier lifetime (τeff)

Figure 5 shows temperature-dependence of the minority carrier effective lifetime (τeff) for Sample (1) prepared with gas-heating turned on before deposition starts and for Sample (2) prepared with gas-heating turned on after deposition starts. The Tmesh, the H content (CH), the bandgap (Eg), and the valence band offset (ΔEv) for the two samples are summarized in Table 1. The higher CH and Eg suggest lower Tsub for Sample (1). Since the thermometer was more sensitive for gas-heating than for heater-heating from below substrate holder because of the positioning of the sensor, as mentioned in Section 2, the real Tsub would be lower for Sample (1). The Eg values of the a-Si:H in Table 1 are relatively narrow for an a-Si:H. This would lead to more parasitic absorption loss compared to films deposited with conventional PECVD when integrated into SHJ solar cells.

It was demonstrated by the results from previous study, ΔEv affects τeff and temperature-dependence of τeff, according to surface recombination model [16]. The behavior of τeff for different ΔEv shown in Figure 5 is qualitatively in good agreement with the result of the simulation in the previous study [16]. Although the effect of ΔEv on the temperature-dependence of τeff is similar to the result of the previous report, the temperatures corresponding to the maximum τeff, T(τmax), are different. In the previous report, T(τmax) decreases with decreasing the Eg of the passivation layer and T(τmax) for the Eg of 1.76 eV is smaller than 60 °C. On the other hand, our experimental results showed that T(τmax) for the Eg of 1.67 eV and 1.62 eV are 100 °C and 70 °C, respectively. This difference between our results and the results shown in the previous report can be explained by the following two possible reasons.

The first possible reason is the difference of interface defect density. As reported in the previous report, the temperature-dependence of τeff is strongly influenced by interface defect density when ΔEv is small. Higher interface defect density leads to higher T(τmax). The τeff of our sample is smaller than that of the sample shown in the previous report, suggesting that interface defect density of our sample is higher than that of the sample shown in the previous reports, probably due to the difference of the thickness of the passivation layer, other than the difference in τbulk. The fact that our samples had been slightly degraded due to air exposure before the measurement of the temperature-dependence of τeff should also be one reason: the degraded τeff values recovered incompletely by annealing, thus the τeff decreased by 25–35% from the initial values due to air exposure. This effect is a possible explanation for why our experimental results show higher T(τmax). The other possible explanation is that electron affinity of our passivation layer and the passivation layer reported in the previous report is different. If the electron affinity of the passivation layer is larger by 0.15 eV for our samples, T(τmax) of our samples are quantitatively in good agreement with the previous report. This is due to the increase of the ΔEv by increasing the electron affinity. The electron affinity of a-Si:H estimated experimentally is 3.93 ± 0.07 eV [24], and the conduction band offset reported previously is 0.15 ± 0.07 eV [25], then, electron affinity of a-Si:H may vary in this range. Thus, the difference of the electron affinity could also be one possible explanation for why our experimental results show higher T(τmax), and it might be one possible reason for high-quality surface passivation, as well.

thumbnail Fig. 5

Temperature-dependence of the minority carrier effective lifetime (τeff) for Sample (1) prepared with gas-heating turned on before deposition starts and for Sample (2) prepared with gas-heating turned on after deposition starts.

Table 1

Comparison of Sample (1) and Sample (2).

4 Conclusion

We fabricated a-Si:H passivation layers on the surfaces of Si wafers by using triode-type PECVD with gas-heating system [5], for SHJ solar cell application. The sample corresponding to the maximum (CH SiH2 + CH SiH3)/CH exhibits the highest passivation quality among the samples prepared with different Tmesh and/or Tsub. This suggests that using SiHx(x=2,3)-rich a-Si:H grown at low Tsub as a passivation layer is advantageous to inhibit an undesirable epitaxial growth at the a-Si:H/c-Si interface, consistently with the previous studies [17,18].

The (CH SiH2+CH SiH3)/CH of a-Si:H was found to be reduced with gas-heating as well as the triode technique. Thus, the importance to use a low Tsub and to optimize gas-heating and the triode technique, for obtaining simultaneously higher film quality and abrupt interface, is suggested. Low S values obtained for our unoptimized samples imply the potency of this deposition technique. Nevertheless, further studies, with precise monitoring and controlling of Tsub, are needed to elucidate the impact of gas-heating and the triode technique on Si surface passivation.

Besides, temperature-dependent τeff for our samples might suggest large ΔEv resulted from relatively large electron affinity for an a-Si:H, which might be one possible reason for high-quality surface passivation.

Acknowledgments

The authors would like to thank Professor A. Matsuda of Osaka University as well as Professor Y. Ichikawa of Tokyo City University, for beneficial suggestions on the gas-heating system in triode-type PECVD reactor. They would like to thank also Dr. K. Nakada of Tokyo Tech for helpful support on experimental points in the laboratory.

Author contribution statement

Conceptualization, designing deposition system, and sample preparation, C. Niikura; Characterization and data analysis, C. Niikura, Y. Shiratori; Writing - original draft, C. Niikura; Writing - review and editing, S. Miyajima, Y. Shiratori; Supervision, S. Miyajima; Resources, S. Miyajima, C. Niikura.

References

  1. S.Y. Herasimenka, W.J. Dauksher, S.G. Bowden, Appl. Phys. Lett. 103, 053511 (2013) [Google Scholar]
  2. S. Tohoda, D. Fujishima, A. Yano, A. Ogane, K. Matsuyama, Y. Nakamura, N. Tokuoka, H. Kanno, T. Kinoshita, H. Sakata, M. Taguchi, E. Maruyama, J. Non-Cryst. Solids 358, 2219 (2012) [CrossRef] [Google Scholar]
  3. K. Masuko, M. Shigematsu, T. Hashiguchi, D. Fujishima, M. Kai, N. Yoshimura, T. Yamaguchi, Y. Ichihashi, T. Mishima, N. Matsubara, T. Yamanishi, T. Takahama, M. Taguchi, E. Maruyama, S. Okamoto, IEEE J. Photovolt. 4, 1433 (2014) [CrossRef] [Google Scholar]
  4. K. Yoshikawa, W. Yoshida, T. Irie, H. Kawasaki, K. Konishi, H. Ishibashi, T. Asatani, D. Adachi, M. Kanematsu, H. Uzu, K. Yamamoto, Solar Energy Mater. Solar Cells 173, 37 (2017) [CrossRef] [Google Scholar]
  5. G. Ganguly, H. Nishio, A. Matsuda, Appl. Phys. Lett. 64, 3581 (1994) [Google Scholar]
  6. A. Matsuda, T. Kaga, H. Tanaka, K. Tanaka, J. Non-Cryst. Solids 59-60, 687 (1983) [CrossRef] [Google Scholar]
  7. T. Matsui, K. Maejima, A. Bidiville, H. Sai, T. Koida, T. Suezaki, M. Matsumoto, K. Saito, I. Yoshida, M. Kondo, Jpn. J. Appl. Phys. 54, 08KB10 (2015) [Google Scholar]
  8. C. Niikura, A. Chowdhury, B. Janthong, P. Sichanugrist, M. Konagai, Appl. Phys. Express 9, 042301 (2016) [CrossRef] [Google Scholar]
  9. Y. Hishikawa, M. Sasaki, S. Tsuge, S. Tsuda, Jpn. J. Appl. Phys. 33, 4373 (1994) [Google Scholar]
  10. H. Fujiwara, M. Kondo, Appl. Phys. Lett. 90, 013503 (2007) [Google Scholar]
  11. S. De Wolf, M. Kondo, Appl. Phys. Lett. 90, 042111 (2007) [Google Scholar]
  12. A. Matsuda, Plasma Phys. Control. Fusion 39, A431 (1997) [Google Scholar]
  13. R.A. Sinton, A. Cuevas, Appl. Phys. Lett. 69, 2510 (1996) [Google Scholar]
  14. D.K. Schroder, Semiconductor Material and Device Characterization (John Wiley & Sons, Inc., Hoboken, 1990) [Google Scholar]
  15. A.A. Langford, M.L. Fleet, B.P. Nelson, W.A. Lanford, N. Maley, Phys. Rev. B 45, 13367 (1992) [Google Scholar]
  16. M. Inaba, S. Todoroki, K. Nakada, S. Miyajima, Jpn. J. Appl. Phys. 55, 04ES04 (2016) [Google Scholar]
  17. W. Liu, L. Zhang, R. Chen, F. Meng, W. Guo, J. Bao, Z. Liu, J. Appl. Phys. 120, 175301 (2016) [Google Scholar]
  18. H. Sai, P.-W. Chen, H.-J. Hsu, T. Matsui, S. Nunomura, K. Matsubara, J. Appl. Phys. 124, 103102 (2018) [Google Scholar]
  19. D.K. Biegelsen, R.A. Street, C.C. Tsai, J.C. Knights, Phys. Rev. B 20, 4839 (1979) [Google Scholar]
  20. J.C. Knights, Jpn. J. Appl. Phys. 18, 101 (1979) [Google Scholar]
  21. S. Yamasaki, S. Kuroda, K. Tanaka, Solid State Commun. 50, 9 (1984) [Google Scholar]
  22. S. Shimizu, M. Kondo, A. Matsuda, J. Appl. Phys. 97, 033522 (2005) [Google Scholar]
  23. Y. Zhang, C. Yu, M. Yang, L.-R. Zhang, Y.-C. He, J.-Y. Zhang, X.-X. Xu, Y.-Z. Zhang, X.-M. Song, H. Yan, Chin. Phys. Lett. 34, 038101 (2017) [CrossRef] [Google Scholar]
  24. H. Matsuura, T. Okuno, H. Okushi, K. Tanaka, J. Appl. Phys. 55, 1012 (1984) [Google Scholar]
  25. R. Varache, J.P. Kleider, W. Favre, L. Korte, J. Appl. Phys. 112, 123717 (2012) [Google Scholar]

Cite this article as: Chisato Niikura, Yuta Shiratori, Shinsuke Miyajima, Si surface passivation by using triode-type plasma-enhanced chemical vapor deposition with thermally energized film-precursors, Eur. Phys. J. Appl. Phys. 89, 10101 (2020)

All Tables

Table 1

Comparison of Sample (1) and Sample (2).

All Figures

thumbnail Fig. 1

Our triode-type PECVD reactor with gas-heating system.

In the text
thumbnail Fig. 2

Total bonded hydrogen content (CH) and (CH SiH2 +CH SiH3)/CH versus mesh temperature (Tmesh), where the CH SiH2 and the CH SiH3 are hydrogen contents in Si = H2 and Si≡H3, respectively, for as-deposited or 250 °C-annealed samples with ∼12 nm thick a-Si:H layers. The data for an as-deposited sample with ∼8 nm thick a-Si:H layers prepared without gas-heating is also shown on the left side of the figure.

In the text
thumbnail Fig. 3

Surface recombination velocity (S) versus post-deposition annealing temperature (Tann) for samples with 6 or 12 nm thick a-Si:H passivation layers prepared with different mesh temperature (Tmesh). Note that the thickness of the sample prepared without gas-heating was exceptionally ∼8 nm.

In the text
thumbnail Fig. 4

TEM cross-sectional image for the sample with ∼12 nm thick a-Si:H layers prepared with a mesh temperature (Tmesh) of 370 °C.

In the text
thumbnail Fig. 5

Temperature-dependence of the minority carrier effective lifetime (τeff) for Sample (1) prepared with gas-heating turned on before deposition starts and for Sample (2) prepared with gas-heating turned on after deposition starts.

In the text

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