A method is presented for controlling an electric field from a gate structure. The method includes forming a hardmask over a fin stack including a plurality of layers, forming a first dielectric layer over the hardmask, forming a sacrificial layer over the first dielectric layer, etching the sacrificial layer to expose a top surface of the first dielectric layer, depositing a second dielectric layer in direct contact with exposed surfaces of the first dielectric layer and the sacrificial layer, removing a layer of the plurality of layers of the fin stack to define an air gap within the fin stack, and forming triangle-shaped epitaxial growths within the air gap defined within the fin stack.