Atomistic Simulations of Device Physics in Monolayer Transition Metal Dichalcogenide Tunneling Transistors

Abstract

© 2015 IEEE.Ballistic transport characteristics of transition metal dichalcogenide (TMDC) tunneling FETs (TFETs) are investigated by atomistic simulations using nonequilibrium Green's function. It is revealed that TMDC TFETs have crystal orientation-dependent transport properties: larger current but smaller utmost limit of ION/IOFF ratio in the zigzag direction (ZD) than in the armchair direction (AD). The orientation-dependent transport is related to the atomistic arrangement in the transport direction and subband properties. A giant negative differential resistance can be obtained in the AD due to the transport valley in the conduction band (CB), while it does not exist in the ZD. Device performance is optimized by tuning doping density and dielectric oxide thickness. Higher source/drain doping concentration can enhance the current at all studied gate voltages but reduce the ION/IOFF ratio, while thinner dielectric oxide thickness can increase saturation current and decrease minimum current at the same time. We also studied the scaling behavior of TMDC TFETs and found that the OFF-state current difference between the two directions gets larger with the gate length. At last, ION as a function of ION/IOFF ratio of six kinds of monolayer M X2 (M = Mo and W; X = S, Se, and Te) TFETs are compared. The largest ON-state current is obtained in WTe2 TFETs at the same ION/IOFF ratio.