**Author details**

density, which is given by the *G*<sup>&</sup>lt; Green's function, the exact Green's function *G* both determines and is determined by the potential *ϕ*. The coupling between Green's function and the Poisson's equation needs to be solved self-consistently. The Hamiltonian in a tight binding (TB) form can be obtained from the Wannier bases naturally. This procedure is called the maximally localized Wannier functions (MLWFs) method [76]. Or it can be obtained by the effective-mass approximation (EMA) and the kp methods. These methods have been successfully utilized to predict the quantum transport behaviors of the devices based on many traditional and 2-D materials [77–87]. It should be noted that in the first principles calculations periodic boundary condition is necessary. As mentioned above, the TFET performance can be improved significantly by vdWHs that are not suitable for the first

We have given a literature survey on recently developed TFETs based on 2-D materials and their vdWHs. Compared with conventional MOSFETs, TFETs mainly work through the BTBT mechanism, resulting in large *I*ON/*I*OFF ratios within small

heterojunctions should be adopted in the TFET design. Then, various novel TFETs based on the vdWHs are studied from structures to working mechanisms. We have also presented the quantum transport simulation method based on the NEGF formalism. However, no 2-D materials vdWH TFET in the experiments exhibits a satisfactorily overall performance. There is still a long way to realize 2-D TFET application. However, we hold an optimistic attitude toward vdWH TFET.

J.C. acknowledges support in part from the Natural Science Foundation of Jiangsu Province under grant number BK20180456 and from the Key Laboratory for Information Science of Electromagnetic Waves (MoE) under grant numbers

supply voltages. To boost the on- and off-state behaviors simultaneously,

principles calculations.

*Integrated Circuits/Microchips*

**Acknowledgements**

**Conflict of interest**

The authors declare no conflict of interest.

EMW201906.

**56**

**7. Conclusions**

Jiang Cao School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, China

\*Address all correspondence to: jiang.cao@njust.edu.cn

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
