Toward a tandem gallium phosphide on silicon solar cell through liquid phase epitaxy growth

Three layers of GaP were epitaxially grown on Si(111) using liquid phase epitaxy (LPE) to demonstrate a path to fabrication of a GaP/Si tandem solar cell. Utilizing a Sn melt with Bi, Mg, and Si additives, direct epitaxial growth on a Si substrate occurred. This was followed by two further epitaxial growths, eliminating Si in the melt, with each layer decreasing in Si concentration. Scanning electron and optical microscopy and electron dispersive spectroscopy were performed in order to determine the characteristics of the growth layers. A fourth layer growth of GaP was attempted utilizing a Ga melt, and the existing structure was able to withstand contact with Ga without dissolution. Epitaxial layers of GaP with a decrease in Si concentration from 10-15% to 6%, then to less than 3%, were accomplished, thereby demonstrating a path to fabrication of a GaP/Si tandem cell using LPE.