Electroeposition of B- and Ni-Doped Silicon from Low-Fluoride Halide Melts

In this study, the effect of dopants such as nickel (Ni) and boron (B) on the structure of deposited silicon obtained from a KCl-CsCl-K ₂ SiF ₆ melt was analyzed. Using cyclic voltammetry, the rate-limiting stages of the process were determined and hypotheses were put forward regarding the mechanism of the influence of dopants on the electrochemical behavior of the system. In the considered systems with different NiO concentrations, silicon deposition is limited at the stage of substance delivery to the cathode surface. Based on the data obtained during the processing of voltammograms, the rate constants of chemical reactions were calculated, based on which conclusions were drawn about the process mechanisms. Thus, the highest process rate is achieved in a system with 0.2 wt. % NiO, in which lnk at a potential scan rate of 1 V/s was − 3.9. Thermodynamic phase diagrams calculated for the operating temperature of the electrolyte allowed us to predict the possible phase composition of the intermetallic compounds obtained during electrolysis. A series of electrolysis experiments were performed, yielding samples of silicon doped with boron or nickel. The morphology of the resulting cathode deposits was studied using scanning electron microscopy. The cathode deposits obtained with the NiO additive are a mixture of fine fibers and silicon crystals, while those with the KBF ₄ additive form long, thin needles spherical crystals with the beginnings of a fibrous structure form on their lateral surfaces. Based on the data obtained, hypotheses were formulated regarding the mechanism by which the additives influence the cathode deposition process.