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).