Heteroepitaxial silicon thin films on flexible polycrystalline metal substrates for crystalline photovoltaic solar cells: A comparison between physical vapor deposition and plasma-enhanced chemical vapor deposition

Heteroepitaxial silicon thin films on low-cost and flexible metal foil substrates is a potential route to inexpensive, high-efficiency electronic devices. Here, we report epitaxial growth of Si thin films on low cost and polycrystalline Ni-alloy based flexible tape as base substrate, using single-crystalline like Ge templates overlying CeO₂/LaMnO₃/MgO buffer layers. Comparison of Si film quality, deposited by two methods namely physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), was conducted. Both approaches result in Si films with similar in-plane texture as evidenced by the X-ray diffraction (XRD) phi-scan results, but Si films deposited by PVD showed more twins defects in z111} plane. Furthermore, Si films deposited by PECVD showed a substantial improvement in the out-of-plane texture as determined by XRD θ-2θ scan, reflection high-energy electron diffraction (RHEED) and Raman spectroscopy. The broader FWHM of PVD Si (400) peak is caused by the higher residual strain and smaller crystallite size. Cross-section transmission electron micrographs revealed relatively a lower dislocation density of Si films compared with Si films previously demonstrated on γ-Al₂O₃.