Anisotropy of impact ionization in WSe2 field effect transistors

Taeho Kang; Haeju Choi; Jinshu Li; Chanwoo Kang; Euyheon Hwang; Sungjoo Lee

doi:10.1186/s40580-023-00361-x

Anisotropy of impact ionization in WSe₂ field effect transistors

Nano Converg. 2023 Mar 17;10(1):13. doi: 10.1186/s40580-023-00361-x.

Authors

Taeho Kang^#^{1

2}, Haeju Choi^#^{1

2}, Jinshu Li^#^{1

2}, Chanwoo Kang^{1

2}, Euyheon Hwang^{3

4

5}, Sungjoo Lee^{6

7

8}

Affiliations

¹ SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 16419, South Korea.
² Department of Nano Science and Technology, Sungkyunkwan University, Suwon, 16419, South Korea.
³ SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 16419, South Korea. euyheon@skku.edu.
⁴ Department of Nano Science and Technology, Sungkyunkwan University, Suwon, 16419, South Korea. euyheon@skku.edu.
⁵ Department of Nano Engineering, Sungkyunkwan University, Suwon, 16419, South Korea. euyheon@skku.edu.
⁶ SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, 16419, South Korea. leesj@skku.edu.
⁷ Department of Nano Science and Technology, Sungkyunkwan University, Suwon, 16419, South Korea. leesj@skku.edu.
⁸ Department of Nano Engineering, Sungkyunkwan University, Suwon, 16419, South Korea. leesj@skku.edu.

^# Contributed equally.

Abstract

Carrier multiplication via impact ionization in two-dimensional (2D) layered materials is a very promising process for manufacturing high-performance devices because the multiplication has been reported to overcome thermodynamic conversion limits. Given that 2D layered materials exhibit highly anisotropic transport properties, understanding the directionally-dependent multiplication process is necessary for device applications. In this study, the anisotropy of carrier multiplication in the 2D layered material, WSe₂, is investigated. To study the multiplication anisotropy of WSe₂, both lateral and vertical WSe₂ field effect transistors (FETs) are fabricated and their electrical and transport properties are investigated. We find that the multiplication anisotropy is much bigger than the transport anisotropy, i.e., the critical electric field (E_CR) for impact ionization of vertical WSe₂ FETs is approximately ten times higher than that of lateral FETs. To understand the experimental results we calculate the average energy of the carriers in the proposed devices under strong electric fields by using the Monte Carlo simulation method. The calculated average energy is strongly dependent on the transport directions and we find that the critical electric field for impact ionization in vertical devices is approximately one order of magnitude larger than that of the lateral devices, consistent with experimental results. Our findings provide new strategies for the future development of low-power electric and photoelectric devices.

Keywords: 2D layered material; Carrier multiplication; Impact ionization; Steep switching; WSe2 field effect transistor.

Grants and funding

2022R1A2C3003068/National Research Foundation of Korea