Techniques for forming a metastable phosphorous P-doped silicon Si source drain contacts are provided. In one aspect, a method for forming n-type source and drain contacts includes the steps of: forming a transistor on a substrate; depositing a dielectric over the transistor; forming contact trenches in the dielectric that extend down to source and drain regions of the transistor; forming an epitaxial material in the contact trenches on the source and drain regions; implanting P into the epitaxial material to form an amorphous P-doped layer; and annealing the amorphous P-doped layer under conditions sufficient to form a crystalline P-doped layer having a homogenous phosphorous concentration that is greater than about 1.5×1021 atoms per cubic centimeter (at./cm3). Transistor devices are also provided utilizing the present P-doped Si source and drain contacts.