Abstract
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 I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sup> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> 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 I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> 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 I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio of six kinds of monolayer MX <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (M = Mo and W; X = S, Se, and Te) TFETs are compared. The largest ON-state current is obtained in WTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TFETs at the same ION/IOFF ratio.
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