  2D material based tunnel FETs are among the most promising candidates for low
power electronics applications since they offer ultimate gate control and high
current drives that are achievable through small tunneling distances during the
device operation. The ideal device is characterized by a minimized tunneling
distance. However, devices with the thinnest possible body do not necessarily
provide the best performance. For example, reducing the channel thickness
increases the depletion width in the source which can be a significant part of
the total tunneling distance. Hence, it is important to determine the optimum
channel thickness for each channel material individually. In this work, we
study the optimum channel thickness for three channel materials: WSe$_{2}$,
Black Phosphorus (BP), and InAs using full-band self-consistent quantum
transport simulations. To identify the ideal channel thickness for each
material at a specific doping density, a new analytic model is proposed and
benchmarked against the numerical simulations.
