Semiconductor device having dopant deactivation underneath gate

A semiconductor device, comprising:

• a substrate;
• a channel region comprising a doped region in the substrate and an undoped epitaxial layer over the doped region, wherein the doped region comprises dopants of a first type, and a bottom surface of the undoped epitaxial layer is below a top-most surface of the substrate;
• a gate structure over the channel region, wherein sidewalls of the gate structure are aligned with sidewalls of the undoped epitaxial layer;
• a source in the substrate, wherein the source comprises dopants of a second type, and the channel region is in direct contact with the source;
• and
• a deactivated region in the substrate and underneath the gate structure, wherein the deactivated region includes the undoped epitaxial layer and a portion of the channel region.

A semiconductor device, comprising:

• a channel region comprising dopants of a first type in a substrate;
• an undoped epitaxial layer over the dopants of the channel region;
• a gate structure over the channel region;
• spacers along sidewalls of the gate structure;
• source/drain regions in the substrate on opposite sides of the gate structure, wherein each of the source/drain regions comprises dopants of second type, and an entirety of the spacers is over the source/drain regions;
• and
• a deactivated region underneath the gate structure wherein dopants within the deactivated region are deactivated, and the deactivated region comprises the undoped epitaxial layer and a portion of the channel region.