Methods for fabricating a fin in a fin field effect transistor (FinFET), include exposing a single crystal fin structure coupled to a substrate of the FinFET. The single crystal fin structure is of a first material. The method further includes implanting a second material into the exposed single crystal fin structure at a first temperature. The first temperature reduces amorphization of the single crystal fin structure. The implanted single crystal fin structure comprises at least 20% of the first material. The method also includes annealing the implanted fin structure at a second temperature. The second temperature reduces crystal defects in the implanted fin structure to form the fin.