A method for forming a transfer gate includes (i) forming a dielectric pillar on a surface of a semiconductor substrate and (ii) growing an epitaxial layer on the semiconductor substrate and surrounding the dielectric pillar. The dielectric pillar has a pillar height that exceeds an epitaxial-layer height of the epitaxial layer relative to the surface. The method also includes removing the dielectric pillar to yield a trench in the epitaxial layer. A pixel includes a doped semiconductor substrate having a front surface opposite a back surface. The front surface forms a trench extending a depth zT with respect to the front surface within the doped semiconductor substrate along a direction z perpendicular to the front surface and the back surface. The pixel has a dopant concentration profile, a derivative thereof with respect to direction z being discontinuous at depth zT.