An apparatus including a transistor device on a substrate including an intrinsic layer including a channel; a source and a drain on opposite sides of the channel; and a diffusion barrier between the intrinsic layer and each of the source and the drain, the diffusion barrier including a conduction band energy that is less than a conduction band energy of the channel and greater than a material of the source and drain. A method including defining an area of an intrinsic layer on a substrate for a channel of a transistor device; forming a diffusion barrier layer in an area defined for a source and a drain; and forming a source on the diffusion barrier layer in the area defined for the source and forming a drain in the area defined for the drain.