Surface-Roughness-Induced Variability in Nanowire InAs Tunnel FETs

We present a comparative study of the surfaceroughness (SR)-induced variability at low supply voltage V_DD = 0.3 V in nanowire InAs tunnel FETs and strained-silicon (sSi) MOSFETs. By exploiting a 3-D full-quantum approach based on the Non-Equilibrium Green´s Function formalism, we show that the I_on variability in InAs tunnel FETs is much smaller than the I_off variability, whereas for V_DD = 0.3 V, the sSi MOSFETs working in the subthreshold regime present similar I_on and I_off variability. We explain the smaller Ion compared with Ioff variability of InAs tunnel FETs by noting that in the source depletion region, where tunneling mainly occurs for V_GS = V_DD, microscopic subband fluctuations induced by SR are small compared to macroscopic band bending due to the built-in potential of the source junction and to the gate bias. This results in SR-induced variability that is larger in InAs tunnel FETs than in sSi MOSFETs.