After forming a gate structure over a semiconductor fin that extends upwards from a semiconductor substrate portion, a sigma cavity is formed within the semiconductor fin on each side of the gate structure. A semiconductor buffer region composed of an un-doped stress-generating semiconductor material is epitaxially growing from faceted surfaces of the sigma cavity. Finally, a doped semiconductor region composed of a doped stress-generating semiconductor material is formed on the semiconductor buffer region to completely fill the sigma cavity. The doped semiconductor region is formed to have substantially vertical sidewalls for formation of a uniform source/drain junction profile.