Silicon Electrodeposition in a Water-Soluble KF–KCl Molten Salt: Properties of Si Films on Graphite Substrates

Abstract

The electrodeposition of crystalline Si films on graphite substrates was investigated in KF–KCl molten salts at 1073 K. The optimum K₂SiF₆ concentration and current density to obtain adherent, compact, and smooth films were investigated using surface and cross-sectional scanning electron microscopy. The crystallinity of the deposited Si films was measured by X-ray diffraction and electron backscatter diffraction techniques. By photoelectrochemical measurements in CH₃CN–TBAPF₆–Fc at room temperature, the Si film electrodeposited on the graphite substrate at 100 mA cm−₂ for ₃0 min in molten KF–KCl–K₂SiF₆ (3.5 mol%) was found to be an n-type semiconductor. When SiCl₄ was used as the Si source, the melt with a higher molar ratio of KF deposited smoother Si films on the graphite substrates. The Si films electrodeposited in molten KF–KCl after the introduction of SiCl₄ gas (2.37 mol%) were confirmed to be p-type by photoelectrochemical measurements in CH₃CN–TBAClO₄–EVBr₂. The characteristics of the electrodeposited Si film (p-type or n-type) is determined by the contaminating impurities (B, P, and Al).