A contiguous block of a stack of two heterogeneous semiconductor layers is formed over an insulator region such as shallow trench isolation. A portion of the contiguous block is exposed to an etch, while another portion is masked during the etch. The etch removes an upper semiconductor layer selective to a lower semiconductor layer in the exposed portion. The etch mask is removed and the entirety of the lower semiconductor layer within the exposed region is metallized. A first metal semiconductor alloy vertically abutting the insulator region is formed, while exposed surfaces of the stack of two heterogeneous semiconductor layers, which comprises the materials of the upper semiconductor layer, are concurrently metallized to form a second metal semiconductor alloy. An inflection point for current and, consequently, a region of flux divergence are formed at the boundary of the two metal semiconductor alloys.