Tunnel field effect transistors

A semiconductor device comprising:

• a first drain region of a first conductivity type disposed in a first region of a substrate;
• a first source region of a second conductivity type disposed in said substrate, said second conductivity type being opposite said first conductivity type;
• a first channel region of the first conductivity type electrically coupled between said first source region and said first drain region;
• a first gate stack overlying said first channel region;
• a first doped region of the first conductivity type disposed between the first source region and the first drain region, wherein the first doped region is doped to a lower doping than the first source region, and wherein at least a portion of the first doped region is in direct contact with a bottom surface of the first channel region;
• and
• a second doped region of the second conductivity type disposed between the first source region and the first drain region, wherein the second doped region is doped to a higher doping than the first doped region, wherein at least a portion of the second doped region is in direct contact with the bottom surface of the first channel region, and
• wherein a tunnel junction is formed at the intersection between the first source region and the first channel region, wherein the first channel region has a lower dopant concentration than a dopant concentration of the first source region so that, at the tunnel junction between the first source region and the first channel region, a net doping concentration varies abruptly from the first source region to the first channel region.