Microcrystalline silicon thin-film, which is one of the promising materials for solar cells, is grown by plasma-enhanced chemical vapor deposition. It is desirable to elucidate the atomistic growth mechanisms to control the defect density and crystal grains. In this study, we simulated the thin-film silicon growth of H-terminated Si(001) by continuous SiH3 and SiH2 radical irradiation using our developed crystal growth simulator based on quantum chemical molecular dynamics method.1 During the SiH3 deposition process, the growth mechanism consists of two stages. The first SiH3 radical abstracts a terminating hydrogen atom, and a dangling bond and a SiH4 molecule are generated. Then, the second SiH3 radical is adsorbed on the dangling bond. Therefore, the two SiH3 radicals are necessary to form a new Si-Si bond. On the other hand, a SiH2 radical can be directly adsorbed on a H-terminated site without hydrogen abstraction. We found that the SiH2 direct adsorption consists of two-step chemical reaction: (1) the SiH2 radical abstracts the hydrogen atom and produces a dangling bond and SiH3 radical, and then (2) the SiH3 radical is adsorbed on the dangling bond. It accounts for the PVD-like process suggested in the experimental results and is in agreement with our density functional calculations. Therefore, one SiH2 radical is sufficient to form a new Si-Si bond. The different growth mechanisms provide the fact that the growth rate for SiH2 radicals is higher than that for SiH3 radicals. However, SiH2 deposition produces a defective silicon film due to a polymer formation. We suggest that SiH3 deposition prompts a layer-by-layer growth and produces a high quality film.2 1 T. Kuwahara et al., J. Phys. Chem. C. 116, 12525 (2012).2 T. Kuwahara et al., submitted.

Quantum chemical molecular dynamics study on film growth mechanisms of microcrystalline silicon solar cells

246th National Meeting (2013)

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