In n/i/n or p/i/p devices the gate controls the thermionic emission current . Aggressively scaled devices of this type suffer from charge pile-up in the channel [273,274], which deteriorates the off-current substantially and ultimately limits the achievable ratio . To overcome this obstacle a gate-controlled tunneling FET (T-CNT-FET) has been proposed .
In T-CNT-FET devices either a p/i/n or n/i/p doping profile can be used. The gate voltage modulates the band to band tunneling current. T-CNT-FETs benefit from a steep inverse sub-threshold slope and a better controlled off-current. In this section the effect of symmetric and asymmetric doping on the device characteristics is discussed.