Junctionless Silicon and In0.53Ga0.47As Transistors—Part II: Device Variability From Random Dopant Fluctuation

Random dopant fluctuation (RDF) variability in nanoscale junctionless FETs (JLFETs) utilizing either Si or In_0.53Ga_0.47As channels has been studied using technology computer-aided design (TCAD) simulations. The 15nm node Si and InGaAs JLFETs are equivalently designed and calibrated using nonequilibrium Green´s function simulations for statistical TCAD analysis. We find that n-InGaAs JLFETs exhibit reduced RDF variability compared with n-Si JLFETs in terms of threshold voltage, subthreshold swing, and drain-induced barrier lowering as a result of high degeneracy effects. By contrast, the variability of p-InGaAs JLFETs is comparable with that of n- and p-Si JLFETs because of the larger valence band density of states (DOS). The normalized variations in ON-state drive current are roughly equal (~16%) for all device types, because the major effects of degenerate screening on current transport effectively cancel one another. From these results, we find that high carrier degeneracy in small DOS materials can have a significant effect on the electrostatic integrity of JLFETs in the presence of RDF (especially in subthreshold), and that degenerately doped n-InGaAs devices are slightly (and inherently) more immune to RDF compared with Si JLFETs.