Device isolation in finFET CMOS

Embodiments herein provide approaches for device isolation in a complimentary metal-oxide fin field effect transistor. Specifically, a semiconductor device is formed with a retrograde doped layer over a substrate to minimize a source to drain punch-through leakage. A set of replacement fins is formed over the retrograde doped layer, each of the set of replacement fins comprising a high mobility channel material (e.g., silicon, or silicon-germanium). The retrograde doped layer may be formed using an in situ doping process or a counter dopant retrograde implant. The device may further include a carbon liner positioned between the retrograde doped layer and the set of replacement fins to prevent carrier spill-out to the replacement fins.