Double Gate Tunnel Field Effect Transistor with Extended Source Structure and Impact Ionization Enhanced Current

The double gate tunnel field effect transistor with sandwiched SiGe/Si source extension is discussed. Here in addition to band-to-band tunneling for lower gate voltages, impact ionization sets in for higher gate voltages, boosting the ON state current by a factor of X. A sandwiched layer of Si between SiGe in the source is proposed to enable higher Ge mole fraction on the surface. SiGe is primarily used to exploit higher tunneling rate from the SiGe region and to utilize the large built-in electric field at the junction of SiGe with Si. Different encroachment of SiGe under the gates was explored to find that optimum performance is observed in the range of 2-4 nm extension. We also show that, impact ionization is confined to a very small region in the device and thus ON current increases without raising the reliability concern.