Circuit fabrication methods are provided which include, for example: providing one or more gate structures disposed over a substrate structure, the substrate structure including a first region and a second region; forming a plurality of U-shaped cavities extending into the substrate structure in the first region and the second region thereof, where at least one first cavity of the plurality of U-shaped cavities is disposed adjacent in one gate structure in the first region; and expanding the at least one first cavity further into the substrate structure to at least partially undercut the one gate structure, without expanding at least one second cavity of the plurality of U-shaped cavities, where forming the plurality of U-shaped cavities facilitates fabricating the circuit structure. In one embodiment, the circuit structure includes first and second transistors, having different device architectures, the first transistor having a higher mobility characteristic than the second transistor.