Ballistic Band-to-Band Tunneling in the OFF State in InGaAs MOSFETs

We present quantum transport simulation results for InAs and In_0.7Ga_0.3As double-gate MOSFETs by using an atomistic full-band basis to evaluate the tunneling currents in the OFF state. While InAs has the advantage of lower mass and higher injection velocity, it also has lower bandgap. For low gate bias, the overlap in energy of the valence band in the channel with the source/drain conduction bands results in band-to-band tunneling (BTBT) between source and drain, which clamps the OFF current. Such current can be reduced by increasing the bandgap of the material either by increasing confinement or by lowering the In content, for example, using In_0.7Ga_0.3As. Grading the doping of the source/drain region to create a wider barrier also reduces BTBT, but to a lesser extent.