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Epitaxial growth of silicon by PECVD from SiF4/H2/Ar gas mixtures for photovoltaics

Abstract : This doctoral work aimed to assess the potential of low-temperature (200-300°C) epitaxy by plasma-enhanced chemical vapor deposition (PECVD) using SiF4/H2/Ar gas mixtures for the emitter formation in nPERT solar cells. The first part of this PhD thesis concerned the identification and the optimization of the process conditions to perform lowly strained intrinsic epi-layers with a smooth epi/wafer interface. We also investigated the causes of epitaxy breakdown and found out that a twinning-induced mechanism was responsible. Subsequently we focused on the growth mechanisms by studying the initial stages of growth and a Volmer-Weber growth mode has been highlighted. Finally, the process conditions for intrinsic epitaxy were transferred from a researchPECVD reactor to a 6 inch semi-industrial one. Inhomogeneity and growth rate issues have been tackled by fluid dynamics simulations resulting in the design of a new shower head. Boron-doped epi-layers grown at 300°C with an as-deposited hole concentration of 4.1019 cm-3 and a doping efficiency up to 70 % have been achieved keeping a low mosaicity and a low variation of the lattice parameter. The growth rate in these conditions reached 1.1 Å/s, i.e 15 times higher than what obtained at the beginning of this PhD for boron-doped epi-layers. Finally, the passivation of epitaxial layers has been investigated and lifetimes up to 160 μs for a 200 nm thick intrinsic layer passivated with
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Ronan Leal. Epitaxial growth of silicon by PECVD from SiF4/H2/Ar gas mixtures for photovoltaics. Materials Science [cond-mat.mtrl-sci]. Université Paris Saclay (COmUE), 2017. English. ⟨NNT : 2017SACLX038⟩. ⟨tel-02969502⟩

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