Gallium phosphide epitaxial films for silicon-based multi-junction solar cells grown by liquid phase epitaxy

The growth of thin layers of III-V semiconductors on a silicon platform for multijunction solar cell applications has the benefits of reduced materials cost and standing on the well-developed silicon integrated circuit and solar cell technology. A prime candidate for developing such a platform is gallium phosphide (GaP) because it has a 0.37% lattice mismatch with Si which is favorable for epitaxial growth. Using liquid phase epitaxy (LPE), we grew GaP films on Si (111) substrates. These GaP/Si structures were characterized for physical properties and further processed into solar cells. In order to investigate the affect of GaP growth on a Si solar cell, we also grew GaP layers on Si solar cells fabricated by a phosphorus diffusion process and compared this structure with a baseline Si solar cell with no GaP layer. The GaP/Si and Si solar cell devices were measured for quantum efficiency and IV characteristics and compared to baseline solar cells without a GaP layer. A GaP layer grown on a Si solar cell deteriorated the current and efficiency. A GaP layer grown on a p-type substrate had lower V_OC but currents comparable to that of the baseline Si solar cell.