A method for fabricating a semiconductor device may include receiving a gated substrate comprising a substrate with a channel layer and a gate structure formed thereon, over-etching the channel layer to expose an extension region below the gate structure, epitaxially growing a halo layer on the exposed extension region using a first in-situ dopant and epitaxially growing a source or drain on the halo layer using a second in-situ dopant, wherein the first in-situ dopant and the second in-situ dopant are of opposite doping polarity. Using an opposite doping polarity may provide an energy band barrier for the semiconductor device and reduce leakage current. A corresponding apparatus is also disclosed herein.