Hydrogenation of Phosphorus-Doped Polycrystalline Silicon Films for

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Surfaces, Interfaces, and Applications

Hydrogenation of Phosphorus-doped Polycrystalline Silicon Films for Passivating Contact Solar Cells Thien Ngoc Truong, Di Yan, Christian Samundsett, Rabin Basnet, Mike Tebyetekerwa, Li Li, Felipe Kremer, Andres Cuevas, Daniel MacDonald, and Hieu Nguyen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b19989 • Publication Date (Web): 17 Jan 2019 Downloaded from http://pubs.acs.org on January 18, 2019

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ACS Applied Materials & Interfaces

Hydrogenation of phosphorus-doped polycrystalline silicon films for passivating contact solar cells Thien N. Truong,1* Di Yan,1 Christian Samundsett,1 Rabin Basnet,1 Mike Tebyetekerwa,1 Li Li,2 Felipe Kremer,3 Andres Cuevas,1 Daniel Macdonald1,*, Hieu T. Nguyen1,* 1

Research School of Engineering, College of Engineering and Computer Science, The

Australian National University, Canberra, ACT 2601, Australia 2

Department of Electronic Materials Engineering, Research School of Physics and

Engineering, The Australian National University, Canberra, ACT 2601, Australia 3

Centre for Advanced Microscopy, The Australian National University, Canberra, ACT

2601, Australia *Corresponding

authors:

[email protected] [email protected] [email protected]

1

ACS Paragon Plus Environment

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Abstract We characterize and discuss the impact of hydrogenation on the performance of phosphorusdoped polycrystalline silicon (poly-Si) films for passivating contact solar cells. Combining various characterisation techniques including transmission electron microscopy, energydispersive X-ray spectroscopy, low-temperature photoluminescence spectroscopy, quasisteady-state photoconductance, and Fourier-transform infrared spectroscopy, we demonstrate that the hydrogen content inside the doped poly-Si layers can be manipulated to improve the quality of the passivating contact structures. After the hydrogenation process of poly-Si layers fabricated under different conditions, the effective lifetime and the implied open circuit voltage are improved for all investigated samples (up to 4.75 ms and 728 mV on 1 Ω.cm ntype Si substrates). Notably, samples with very low initial passivation qualities show a dramatic improvement from 350 μs to 2.7 ms and from 668 mV to 722 mV.

Keywords Hydrogenation, doped polycrystalline silicon, amorphous silicon, passivating contacts, photoluminescence.

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Introduction For decades, stacks consisting of a doped polycrystalline silicon (poly-Si) film and an ultrathin silicon oxide (SiOx) layer have been employed in microelectronic devices. They act as active layers in thin-film transistors due to benefits of gain amplification1–3, emitter efficiency enhancement4, resistance reduction5, etc. When a doped poly-Si/SiOx stack is applied to a crystalline Si (c-Si) solar cell, it forms a carrier selective junction and, at the same time, provides excellent surface passivation6–10. These advantages have prompted the development of novel solar cell structures featuring doped poly-Si/SiOx stacks as the carrier selective contacts11–15, enabling the achievement of very high open circuit voltages (Voc) of up to 733 mV and a light-to-electricity power conversion efficiency of 26.1%13. Doped poly-Si passivating contacts can be fabricated by various methods: in situ depositing doped poly-Si layers using a low-pressure chemical-vapour deposition (LPCVD)16 technique at intermediate temperatures (~630 oC), implanting dopants into such LPCVD layers13, implanting dopants into hydrogenated amorphous silicon (a-Si:H) deposited by a plasmaenhanced chemical-vapour deposition (PECVD) technique17,18 or adding dopants in-situ during the PECVD process8,19,20, depositing doped a-Si:H films by atmospheric-pressure chemical-vapour deposition (APCVD)21, or sputtering both the silicon and the dopant22. In all the above cases a high temperature annealing step is required to re-crystallize the Si film and activate the dopants; alternatively, a thermal dopant diffusion process into an intrinsic a-Si:H or poly-Si film can be performed23. In general, the doped poly-Si films often contain a high density of defects, as recently reported by Nguyen et al.24. These defects can potentially affect the quality of the passivating-contact structures and thus the overall performance of the solar cells. On the other hand, the benefits of hydrogenation processes are well-known for c-Si wafers and solar cells25–30. Hydrogenation via a forming gas annealing (FGA)31–33 step or via the deposition of hydrogen-rich thin films such as SiNx:H34–37 or Al2O3:H30,38,39 has been shown to lead to significant improvements in the electrical properties of silicon solar cells by deactivating recombination centres associated with various impurities and defects. Moreover, the use of FGA is also well-known for improving the interface between the c-Si substrate and the poly-Si/SiOx stack in passivating contact solar cells12,30. 3



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In principle, hydrogenation techniques could also be used to passivate defects within the doped poly-Si films themselves, in a similar manner to the c-Si substrates, and thus they could improve the overall performance of doped poly-Si/SiOx passivating contacts. In this work, we explore such possibilities. First, we investigate the microscopic structure of the doped poly-Si/SiOx/c-Si stacks and demonstrate that the doped poly-Si layer contains both amorphous and crystalline silicon phases. We then utilize the distinct luminescence properties of those amorphous and crystalline phases to unambiguously demonstrate bulk hydrogenation of the doped poly-Si film. After that, we assess the effects of hydrogenation on the film’s quality and on its ability to passivate the c-Si substrate, using various independent techniques, including

low-temperature

photoluminescence

(PL)

spectroscopy,

quasi-steady-state

photoconductance (QSSPC), and Fourier-transform infrared spectroscopy (FTIR). The results demonstrate that the hydrogen atoms can passivate non-radiative defects inside the doped poly-Si layer, and thus significantly improve the quality of the overall passivating-contact structure.

Experimental Details For this study, 1 Ω.cm, -oriented float-zone (FZ) n-type c-Si wafers with an initial thickness of ~275 µm were used. After removing possible surface damage in a Tetramethylammonium Hydroxide (TMAH) etching solution, ultra-thin layers of SiOx (~1.3 nm) were grown chemically on both sides. Subsequently, the samples were coated with 100nm layers of PECVD a-Si:H on both sides and subjected to phosphorus diffusion processes at two different temperatures (830 and 860 oC). The resultant phosphorus silicate glass (PSG) layers were removed by means of a diluted hydrofluoric solution (stage 1). Note that during this high temperature step a large fraction of the a-Si becomes polycrystalline, which means that, essentially, the poly-Si/SiOx selective contact structure is already formed. Subsequently, different hydrogenation treatments were performed. In the first of them, the samples were annealed at 500 oC for 30 minutes in a forming gas mixture consisting of argon and hydrogen (stage 2). They were then coated with 80-nm layers of PECVD SiNx:H on both sides, followed by the same forming gas annealing (FGA) process at 500 oC for 30 minutes (stage 3). Finally, the SiNx layers were removed by means of a concentrated HF solution and the samples were annealed again in nitrogen at 600 oC for 2 hours (stage 4). It is expected that after this step (stage 4), all hydrogen should have effused out of the doped poly-Si layers, 4


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thus permitting to investigate their performance in the absence of hydrogen. Figure 1 summarizes the process steps mentioned above. All measurements (PL, QSSPC, and FTIR) were done for each stage (1-4), after the SiNx layers were removed (if present) by a concentrated HF solution. Stage 1

Stage 2

Stage 3

Stage 4

830 (or 860 oC ) phosphorus doped polySi/SiOx/c-Si with PSG removed

Annealing 500oC FGA, 30 mins.

PECVD SiNx:H + 500oC FGA, 30 mins.

Annealing 600oC N2, 2 hrs.

QSSPC

PL

QSSPC

FTIR

TEM

PL

QSSPC

PL

QSSPC

PL

FTIR

Figure 1. Flow chart of the experimental processes. before all measurements if present.

The SiN x layers were removed

Transmission electron microscope (TEM) images were captured using a JEOL JEM-2100F instrument. TEM lamellae were prepared by a focused-ion beam (FIB) milling technique. Element maps were obtained by energy-dispersive X-ray spectroscopy (EDS) accessories in the TEM system. Steady-state micro-PL (μ-PL) spectroscopy measurements were performed using a Horiba Labram system equipped with a confocal microscope. The incident laser beam was focused to a 5-m diameter spot onto the sample surface through a 50× objective lens, and emitted PL signals were directed to a monochromator. A liquid-nitrogen-cooled InGaAs array detector with a detection range between 750 nm and 1600 nm was used to collect steady-state PL signals. The excitation source for the PL measurements was a 405-nm solidstate laser. All PL measurements were performed at 80 K using a THMS600 Linkam stage. Minority carrier lifetime and implied open circuit voltage (iVoc) measurements were performed with a Sinton Instruments WCT-120 contactless photoconductance tester. FTIR experiments were taken in the range of 320 – 4000 cm-1 with a resolution of 4 cm-1.

Results and Discussions

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(a)

(b) Pt

Doped poly-Si

SiOx

c-Si substrate

(d) a-Si DP

Si

3 2 1

O

0

poly-Si Normalized PL intensity (a.u.)

Si SiOx

Doped poly-Si

4

SiOx interface

Intensity (a.u.)

c-Si DP

(c) 5

c-Si

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(e) 1.0

145 Distance (nm)

290

c-Si

0.5 doped poly-Si 0.0 750

1000 1250 1500 Wavelength (nm)

Figure 2. (a) High-angle annular dark-field (HAADF) image of the phosphorous-doped poly-Si/SiO x /c-Si structure. The sample was prepared by FIB milling with a capped platinum layer (bright Pt strip). The scale bar is 20 nm. (b) TEM-EDS elemental mapping of the sample (Si + O + Pt overlayed, Si: orange; O: yellow; Pt: green). The scale bar is 20 nm. (c) TEM-EDS line scan profiles of Si and O with clear peaks representing the SiO x interface. (d) High-resolution TEM image of the selected area, with corresponding diffraction patterns (DPs) from the poly-Si film and c-Si substrate. The scale bar is 2 nm. (e) PL spectra from the phosphorous-diffused poly-Si sample captured at 80 K using the excitation wavelength of 405 nm with a spot size of 5 µm in diameter. The diffusion process is at 860 o C.

First, we demonstrate that the a-Si:H film deposited by the PECVD technique is not fully recrystallized after the phosphorus diffusion process. Figure 2(a) shows a high-angle annular dark-field (HAADF) image of the 100-nm n-doped poly-Si/1.3-nm SiOx /c-Si structure. Figure 2(b) represents the corresponding elemental mapping of silicon (orange colour) and oxygen (yellow colour), clearly showing the position of the intermediate oxide layer. Such 6


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position can also be observed in the EDS line scan profiles of O and Si (Figure 2(c)), with very clear intensity peaks. Figure 2(d) shows a high-resolution TEM image of the interface. The interfacial oxide film can be observed as a thin stripe of amorphous structure between the poly-Si and c-Si, as noted in the figure. The doped poly-Si layer shows both crystalline and amorphous phases, whereas, as expected, the c-Si substrate shows a very uniform crystalline structure. To further confirm the co-existence of crystalline and amorphous phases in the doped poly-Si layer, X-ray diffraction patterns from both the c-Si substrate and the poly-Si layer are also given in Figure 2(d). The diffraction pattern from the doped poly-Si layer contains both amorphous and crystalline signatures, revealed by a series of concentric rings (for the amorphous phase) and discrete bright spots (for the crystalline phase) (see Figure 2(d), right corner), compared to the only bright-spot pattern from the c-Si substrate (Figure 2(d), left corner)40. In addition, Figure 2(e) shows a PL spectrum captured from the 100-nm n+ poly-Si/1.3-nm SiOx/c-Si sample at 80 K, excited with the 405-nm laser. The sharp peak located at ~1125 nm is the band-to-band emission from the c-Si substrate41. The spectrum also contains a very broad peak in the range 1300 - 1400 nm. This broad peak originates from the radiative defect states inside the doped poly-Si layer, as recently reported by Nguyen et al24. However, there is no PL emission from the amorphous Si phase in the doped poly-Si film, which is at stage 1 and not yet hydrogenated. Numerous works have reported a strong PL emission from a-Si:H films deposited on both cSi and glass substrates at low temperatures. The characteristic a-Si:H peak is much broader than the c-Si peak and its position varies between 850 nm and 950 nm depending on deposition conditions42–47 (see Figure S1, Supporting Information). Without hydrogen, amorphous Si films contain an extremely high density of defect states, which likely suppress the broad a-Si:H PL peak. To confirm this hypothesis, we capture the PL spectra from an aSi:H film deposited by PECVD at 300 oC on top of a SiOx/c-Si sample before and after an annealing step at 600 oC in N2 for 2 hours. At this temperature, the amorphous Si film is not recrystallized yet, but hydrogen atoms can be expected to escape out of it. The results in Figure 3 show that this is indeed the case, since the a-Si:H PL peak located at ~850 nm is completely quenched by the 600 oC N2 annealing step. Therefore, it is sensible to assume that after the even higher temperature (>800 0C) used for dopant diffusion, there will be 7



essentially no hydrogen left in the bulk of the poly-Si layer, which explains the absence of an a-Si:H PL peak in Figure 2(e).

1.0

PL Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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a-Si:H/SiOx/c-Si as deposited

a-Si:H

a-Si:H/SiOx/c-Si annealed

0.5

c-Si c-Si

0.0 800

1000

1200

1400

1600

Wavelength (nm)

Figure 3. PL spectra from an a-Si:H/SiO x /c-Si sample before (as deposited by PECVD) and after annealing in nitrogen at 600 o C for 2 hours. The PL spectra are captured at 80K using a 405-nm excitation laser. The c-Si PL peak at around 1125-nm is not observed due to the fact that the 405-nm laser light is mostly absorbed in the 100-nm layer of amorphous silicon film.

The fact, confirmed by TEM and X-ray diffraction, that there are both amorphous and crystalline phases in the doped poly-Si layer, but the amorphous phase does not emit the PL signal commonly attributed to a-Si:H, provides us with a unique opportunity to evaluate the effects of hydrogenation on the doped poly-Si layer. PL spectra captured from a doped polySi sample at various stages (stages 1-4 in Figure 1) are given in Figure 4(a). The spectra at stage 1 (after dopant diffusion) and stage 2 (after FGA) are nearly identical, suggesting that annealing in forming gas at 500 oC does not affect significantly the bulk properties of the doped poly-Si layer and the poly-Si/SiOx interface, although it is known to improve the SiOx/c-Si interface12,30. However, the spectrum at stage 3 (annealed in the presence of a hydrogen-rich SiNx film) shows a very clear peak located at ~900 nm, which matches the characteristic emission from a-Si:H in previous studies47. This is strong evidence that the amorphous Si phase has been hydrogenated. Also, the intensity of the peak corresponding to luminescence from the poly-Si layer increases after the hydrogenation step, indicating that non-radiative defects inside the poly-Si film have also been passivated. In addition, the intensity of the c-Si peak also increases, which indicates an improvement of surface passivation, leading to a higher excess carrier concentration in the c-Si. Although the recombination level at room temperature should be different from that at 80K, the c-Si PL 8


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signal from the hydrogenated sample should be still higher than that from the nonhydrogenated sample at room temperature, as evidenced by the higher effective carrier lifetime in Figure 4(d). (b) c-Si

1-doped poly-Si/SiOx/c-Si

4-Annealing 600oC, 2hrs.

0.5 a-Si:H doped poly-Si

0.0 750

1000

1250 Wavelength (nm)

Diffused at 830oC Diffused at 860oC

1.0

0.5

0.0

1500

1 - doped poly-Si/ SiOx/c-Si

2 - FGA

3 - SiNx:H+FGA 4 - Annealing 600oC, 2hrs.

Stage

(c)

(d) 0.75

6

Minority carrier lifetime (ms)

2.5 Diffused at 830oC Diffused at 860oC 2.0

1.5

1.0

5 4

0.70

3 2

0.65 o

Diffused at 830 C Diffused at 860oC Diffused at 830oC Diffused at 860oC

1 0


2 - FGA

3 - SiNx:H+FGA 4 - Annealing 600oC, 2hrs.

Stage

Implied VOC(V)

PL intensity (a.u.)

2-FGA 3-SiNx:H+FGA

Integrated a-Si:H PL peak (a.u.)

(a) 1.0

Integrated doped poly-Si PL peak (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



2 - FGA

3 - SiNx:H+FGA

0.60 4 - Annealing 600oC, 2hrs.

Stage

Figure 4. (a) PL spectra from phosphorus-diffused poly-Si samples at various stages, captured at 80K using the excitation laser of 405 nm. The phosphorus diffusion temperature is 860 0 C. (b) Integrated PL intensity from the hydrogenated amorphous silicon peak and (c) the doped polycrystalline silicon peak. The integrated intensity of the a-Si:H peak is taken from 750-1000 nm, whereas that of the doped poly-Si peak is taken from 1250-1550 nm after subtracting the contribution of the a-Si:H peak in this wavelength range. (d) Minority-carrier lifetime and implied open circuit voltage of the samples at various stages. The minority carrier density is 1×10 1 5 cm - 3 .

To consolidate these conclusions, we bring the sample to stage 4 (annealing in nitrogen at 600 oC for 2 hours). As shown above, this annealing process removes most of hydrogen from the doped poly-Si layer (from both the crystalline and amorphous phases). As can be seen in Figure 4(a), the emitted PL spectrum goes back to the shape it had at stages 1 and 2, in which the a-Si:H peak is absent and only the doped poly-Si peak is present. Figure 4(b) and 4(c) 9



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show the integrated PL intensities from the a-Si:H peak, taken from 750-1000 nm to avoid overlapping with the c-Si peak, and the doped poly-Si peak, taken from 1250-1550 nm after subtracting the contribution from the a-Si:H peak in this wavelength range (see Figure S2, Supporting Information), at the different experimental stages. It can be seen that the effects of hydrogenation are very clear for both PL peaks and at different diffusion temperatures. It is also noticeable that at the higher diffusion temperature a higher fraction of the amorphous phase has been recrystallized, thus yielding lower a-Si:H PL intensities after hydrogenation. However, Figure 4(c) shows that the doped poly-Si PL intensity at 860 oC is still lower than that at 830 oC. There are, in fact, two competing effects of radiative and non-radiative defects. The doped poly-Si PL peak originates from the radiative defects. The fact that this PL peak is smaller for the higher diffusion temperature (860 oC) could indicate a lower overall defect concentration inside the 860 oC doped poly-Si film, compared to the 830 oC case. However, within the same film, after hydrogenation, the non-radiative defects should be hydrogenated, yielding the higher intensity of the doped poly-Si PL peak. Next we investigate the impact of hydrogenation on the effective minority carrier lifetime (at a minority carrier density of 1×1015 cm-3) and the implied open circuit voltage (iVoc) (at 1-sun intensity) of silicon wafers coated on both sides with a poly-Si/SiOx passivating contact. The results are shown in Figure 4(d). After FGA (stage 2), the passivation quality increases for both phosphorus diffusion temperatures, even though there is little change in the PL spectrum from the doped poly-Si layer itself, as shown in Figure 4(a). These two pieces of evidence indicate that only the SiOx/c-Si interface is improved by the FGA step at stage 2. After stage 3, however, hydrogen atoms from the SiNx:H have been introduced into both the poly-Si film and the SiOx/c-Si interface, thus resulting in a further improvement of the passivation quality. The improvement is particularly important for the sample prepared at 830 oC diffusion temperature, because its initial effective lifetime and iVoc were very low (340 μs and 668 mV, respectively). After hydrogenation, both the lifetime and iVoc increase significantly (>2.5 ms and >720 mV, Figure 4d). These observations were also made for samples where the FGA step of stage 2 was skipped, that is, for samples that went directly from the formation of the doped poly-Si film (stage 1) to the SiNx-assisted hydrogenation process (stage 3) (see Figure S3, Supporting Information).

10


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It is interesting to note that the performance of passivating contacts formed at the higher temperature of 860 oC is even better than that of layers formed at 830 oC, both before and after hydrogenation. This shows that there is a complex interplay between levels of crystallinity, doping and hydrogenation. It is clear, however, that the presence of hydrogen in the poly-Si film is correlated with achieving high quality passivation. After stage 4 (annealed again in N2 at 600 oC for 2 hours), the lifetimes and iVoc drop dramatically due to the absence of hydrogen inside the films. However, the effective carrier lifetime at stage 4 is less than that at stage 1. This suggests that there should be other unknown mechanisms that could influence the overall carrier lifetime. For example, after being annealed at 600 oC, the float-zone sample may experience the “dead zone” thermal activating defects according to Grant et al.48 Finally, we also verify the presence of Si-H bonds in the poly films using FTIR measurements, as shown in Figure 5. Comparing the absorbance spectra of the doped polySi/SiOx/c-Si stacks with and without hydrogenation, the sample with hydrogenation clearly shows the stretching mode of Si-H bonds at around 2100 to 2200 cm-1, consistent with the reported value in the literature49–52. This observation is valid for all the hydrogenated samples, prepared at various dopant diffusion temperatures. (a) 830 oC

(b) 860 oC Si-H

1.0

Absorbance (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.5

0.0

Without hydrogenation With hydrogenation

-0.5

1900

2000

2100

2200

2300

Wavenumber (cm-1)

Figure 5. FTIR spectra of the samples phosphorus diffused at (a) 830 o C and (b) 860 o C with and without hydrogenation. The negative baselines are due to the different backgrounds between the calibration c-Si wafer and the investigated samples.

Conclusion In summary, we have identified significant hydrogenation effects in the bulk of phosphorusdoped polycrystalline silicon layers and their application for improving solar cell passivating 11



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contacts. The silicon films were found to contain both amorphous and crystalline phases, each yielding a distinct luminescence peak at low measurement temperatures. We have then employed various independent characterization techniques to verify the presence of hydrogen inside the films after the hydrogenation process. The results have demonstrated that hydrogen can be introduced into the doped silicon films to improve the quality of the poly-Si/SiOx passivating contacts. We have corroborated the technique on various initial low-quality doped polycrystalline silicon films, all of which have been improved significantly after the hydrogenation process. These characterization and hydrogenation techniques open an exciting avenue for optimizing passivating-contact structures.

Acknowledgments This work has been supported by the Australian Renewable Energy Agency (ARENA) through Research Grant RND017 and the Australian Centre for Advanced Photovoltaics (ACAP) Collaboration Grant. The authors acknowledge the facility and technical support from the Australian National Fabrication Facility (ANFF), ACT Node and the Australian Microscopy & Microanalysis Research Facility at the Centre of Advanced Microscopy, The Australian National University. The authors thank Dr Ziv Hameiri at the University of New South Wales for performing FTIR measurements. H.T.N. acknowledges the fellowship support from the ACAP. M.T. acknowledges the research support from the Australian Government Research Training Program (RTP) Scholarship.

Author Contributions H.T.N. conceived the idea, designed the overall experiments, and supervised the project. D.M. co-supervised the project. T.N.T. fabricated samples and performed measurements. D.Y., C.S., R.B., M.T., L.L., and F.K. contributed to the material fabrication, characterisation and experimental setup. A.C. and D. M. contributed to the data analysis. T.N.T. and H.T.N. analysed the data and wrote the manuscript. All authors contributed to the discussion of the results and reviewed the manuscript.

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Graphic for manuscript: 405 nm 1.0

a-Si:H c-Si

PL

H 0.5

0.0

Si

Hydrogenation

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


800

poly-Si

1000 1200 1400 Wavelength (nm)

1600

P Poly-Si SiOx c-Si

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Hydrogenation of Phosphorus-Doped Polycrystalline Silicon Films for

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