Integrated circuits include fins including an upper/channel region and a lower/sub-channel region, the lower region having a first chemical composition and opposing sidewalls adjacent to an insulator material, and the upper region having a second chemical composition. A first width indicates the distance between the opposing sidewalls of the lower region at a first location is at least 1 nm wider than a second width indicating the distance between the opposing sidewalls of the upper region at a second location, the first location being within 10 nm of the second location (or otherwise relatively close to one another). The first chemical composition is distinct from the second chemical composition and includes a surface chemical composition at an outer surface of the opposing sidewalls of the lower region and a bulk chemical composition therebetween, the surface chemical composition including one or more of oxygen, nitrogen, carbon, chlorine, fluorine, and sulfur.