Methods of fabricating field effect transistors having a source region and a drain region separated by a channel region are provided which include: using a single mask step in forming a first portion(s) and a second portion(s) of at least one of the source region or the drain region, the first portion(s) including a first material selected and configured to facilitate the first portion(s) stressing the channel region, and the second portion(s) including a second material selected and configured to facilitate the second portion(s) having a lower electrical resistance than the first portion(s). One embodiment includes: providing the first material with a crystal lattice structure; and forming the second material by disposing another material interstitially with respect to the crystal lattice structure. Another embodiment includes forming the first portion and the second portion within at least one of a source cavity or a drain cavity of the semiconductor substrate.