Modeling the Effect of Interface Roughness on the Performance of Tunnel FETs

The sub-band formation in the triangular-like potential well in the channel of a tunnel field effect transistor (TFET) results in a delayed onset of the vertical band-to-band tunneling (BTBT) and in a reduction of the ON-current. Furthermore, the roughness of the oxide/semiconductor interface causes density-of-states (DOS) tails, i.e., a smoothing of the otherwise staircase-shaped 2D DOS in the TFET channel. The impact of interface roughness is modeled semi-classically using Ind's perturbation approach. The developed model for the combined effect of the channel quantization and interface roughness on TFET performance has been implemented in a commercial device simulator. Simulations of a TFET with predominantly vertical BTBT show that the sharp onset of tunneling, which ideally originates from the 2D-3D DOS matching, is smoothed by the interface roughness. This leads to a degradation of the sub-threshold swing of the transistor with increasing amplitude and decreasing auto-correlation length of the roughness.