Abstract-Dual-junction solar cells formed by a GaAsP cell on a silicon bottom cell seem to be attractive candidates to materialize the long sought-for integration of III-V materials on Si for photovoltaic applications. In this study, we analyze several factors for the optimization of the bottom cell, namely, 1) the emitter formation as a result of phosphorus diffusion; 2) the growth of a high quality GaP nucleation layer; and 3) the process impact on the bottom subcell PV properties.