Effects of nanoparticle incorporation on properties of microcrystalline films deposited using multi-hollow discharge plasma CVD
Highlights
► We studied the effects of Si nanoparticles on photo, dark conductivity of μc-Si film. ► Incorporation of nanoparticles decreases photo and dark conductivity. ► Nanoparticles increase photosensitivity due to their lower dark conductivity. ► Nanoparticles effects depend on their volume fraction of the film.
Introduction
Plasma enhanced chemical vapor deposition (PECVD) is widely used for production of microcrystalline silicon (μc-Si) thin films of amorphous silicon/microcrystalline silicon (a-Si/μc-Si) tandem solar cells [1], [2], [3], [4], [5], [6], [7]. In this PECVD process growth of the films has often been discussed in terms of contribution of SiH3 radicals and atomic hydrogen [8], even though contribution of other species such as ions and SiH2, Si2H4, Si2H5, and so on should be considered [9], [10], [11], [12]. Moreover Si nanoparticles produced in SiH4 plasmas can be incorporated into films [13], [14], [15], and such incorporation may change considerably their electronic [16], [17], [18], [19], [20], [21] and optical properties [22], [23], [24], [25] depending on the size, structure, and volume fraction of nanoparticles incorporated into films. So far little information about the effects of nanoparticle incorporation on properties of microcrystalline Si films has been reported.
Here we have studied such effects of nanoparticle incorporation using a multi-hollow discharge plasma CVD reactor with which films with and without nanoparticles can be simultaneously deposited. We report clear experimental results showing that incorporation of small amount of crystalline nanoparticles into films strongly affects electrical property of microcrystalline Si films.
Section snippets
Experimental
Si films were deposited using a multi-hollow discharge plasma CVD reactor by which incorporation of nanoparticles into films could be significantly suppressed in the upstream region by setting the gas flow velocity high enough to drive nanoparticles toward the downstream region as shown in Fig. 1 [15]. Thus Si films without incorporating nanoparticles were deposited in the upstream region, whereas Si films with incorporating nanoparticles were deposited in the downstream region. Multi-hollow
Results and discussion
Fig. 2 shows typical two dimensional images of films deposited for R = 30, the deposition time of 2 min and R = 40, the deposition time of 21 min respectively. Brown regions indicate the deposited regions. By analyzing these upstream and downstream films we studied effects of incorporation of nanoparticles into films as a parameter of dilution ratio R.
Fig. 3 shows dependence of (a) the deposition rate and (b) crystallinity XC of films on the distance z from the discharges as a parameter of dilution
Conclusions
Effects of incorporation of crystalline nanoparticles into Si films on their electrical and photoelectrical properties have been studied using multi‐hollow discharge plasma CVD. Following conclusions are obtained in this study.
- 1)
Films with nanoparticles show lower photo and dark conductivity than those without nanoparticles, whereas both films have nearly the same crystallinity.
- 2)
Films with nanoparticles have higher photosensitivity than the films without nanoparticles.
- 3)
Microcrystalline films of
Acknowledgments
This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT).
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