  In this work, vertical tunnel field-effect transistors (v-TFETs) based on
vertically stacked heretojunctions from 2D transition metal dichalcogenide
(TMD) materials are studied by atomistic quantum transport simulations. The
switching mechanism of v-TFET is found to be different from previous
predictions. As a consequence of this switching mechanism, the extension
region, where the materials are not stacked over is found to be critical for
turning off the v-TFET. This extension region makes the scaling of v-TFETs
challenging. In addition, due to the presence of both positive and negative
charges inside the channel, v-TFETs also exhibit negative capacitance. As a
result, v-TFETs have good energy-delay products and are one of the promising
candidates for low power applications.
