Silicon Electrodeposition in a Water-Soluble KF–KCl Molten Salt: Properties of Si Films on Graphite Substrates
Kouji Yasuda, Tomonori Kato, Yutaro Norikawa, Toshiyuki Nohira
Abstract
The electrodeposition of crystalline Si films on graphite substrates was investigated in KF–KCl molten salts at 1073 K. The optimum K 2 SiF 6 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 CH 3 CN–TBAPF 6 –Fc at room temperature, the Si film electrodeposited on the graphite substrate at 100 mA cm −2 for 30 min in molten KF–KCl–K 2 SiF 6 (3.5 mol%) was found to be an n-type semiconductor. When SiCl 4 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 SiCl 4 gas (2.37 mol%) were confirmed to be p-type by photoelectrochemical measurements in CH 3 CN–TBAClO 4 –EVBr 2 . The characteristics of the electrodeposited Si film (p-type or n-type) is determined by the contaminating impurities (B, P, and Al).