A semiconductor structure includes a fin upon a semiconductor substrate. A clean epitaxial growth surface is provided by forming a buffer layer upon fin sidewalls and an upper surface of the fin. The buffer layer may be epitaxially grown. Diamond shaped epitaxy is grown from the buffer layer sidewalls. In some implementations, the diamond shaped epitaxy may be subsequently merged with surrounding dielectric. A dopant concentration of the surrounding dielectric may be higher than a dopant concentration of the diamond shaped epitaxy.