In some implementations, the method further includes reducing a width of the fin structure before forming the doped amorphous silicon layer. In such implementations, a thickness of the doped amorphous layer is about equal to an amount of the fin structure removed when reducing the width of the fin structure, and the knock-on implantation process causes the doped amorphous silicon layer to become a part of the fin structure. In some implementations, the knock-on implantation process causes a portion of the doped amorphous silicon layer to become a part of the fin structure. In such implementations, the method further includes oxidizing a remaining portion of the doped amorphous silicon layer, and removing the oxidized portion of the doped amorphous silicon layer.

Yet another exemplary method includes forming a fin structure. The fin structure includes a channel region defined between a source region and a drain region. The fin structure further includes a material having a crystalline structure. The method further includes forming a gate structure over the channel region of the fin structure. The method further includes forming a doped layer over the source region and the drain region of the fin structure. The doped layer includes the material having a non-crystalline structure. The method further includes performing a knock-on implantation process to drive a dopant from the doped layer into the source region and the drain region of the fin structure, wherein the knock-on implantation process converts a portion of the doped layer into the material having the crystalline structure.