Spatially Bandgap-Graded MoS2(1-x)Se2x Homojunctions for Self-Powered Visible-Near-Infrared Phototransistors

Hao Xu; Juntong Zhu; Guifu Zou; Wei Liu; Xiao Li; Caihong Li; Gyeong Hee Ryu; Wenshuo Xu; Xiaoyu Han; Zhengxiao Guo; Jamie H Warner; Jiang Wu; Huiyun Liu

doi:10.1007/s40820-019-0361-2

Spatially Bandgap-Graded MoS_2(1-x)Se_2x Homojunctions for Self-Powered Visible-Near-Infrared Phototransistors

Nanomicro Lett. 2020 Jan 18;12(1):26. doi: 10.1007/s40820-019-0361-2.

Authors

Hao Xu^#¹, Juntong Zhu^#², Guifu Zou³, Wei Liu^{4

5}, Xiao Li⁴, Caihong Li⁶, Gyeong Hee Ryu⁷, Wenshuo Xu⁷, Xiaoyu Han⁸, Zhengxiao Guo^{8

9

10}, Jamie H Warner⁷, Jiang Wu^{11

12}, Huiyun Liu⁴

Affiliations

¹ Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK. xuhaosilvia@gmail.com.
² School of Energy, Soochow Institute for Energy and Materials Innovations, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province, Soochow University, Suzhou, 215006, People's Republic of China.
³ School of Energy, Soochow Institute for Energy and Materials Innovations, and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province, Soochow University, Suzhou, 215006, People's Republic of China. zouguifu@suda.edu.cn.
⁴ Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK.
⁵ London Centre for Nanotechnology, University College London, London, WC1H 0AH, UK.
⁶ Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, 610054, People's Republic of China.
⁷ Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
⁸ Department of Chemistry, University College London, 20 Gordon St, Bloomsbury, London, WC1H 0AJ, UK.
⁹ Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China.
¹⁰ Zhejiang Institute of Research and Innovation, The University of Hong Kong, Qingshan Lake SciTech City, Hangzhou, People's Republic of China.
¹¹ Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK. jiangwu@uestc.edu.cn.
¹² Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, 610054, People's Republic of China. jiangwu@uestc.edu.cn.

^# Contributed equally.

Abstract

Ternary transition metal dichalcogenide alloys with spatially graded bandgaps are an emerging class of two-dimensional materials with unique features, which opens up new potential for device applications. Here, visible-near-infrared and self-powered phototransistors based on spatially bandgap-graded MoS_2(1-x)Se_2x alloys, synthesized by a simple and controllable chemical solution deposition method, are reported. The graded bandgaps, arising from the spatial grading of Se composition and thickness within a single domain, are tuned from 1.83 to 1.73 eV, leading to the formation of a homojunction with a built-in electric field. Consequently, a strong and sensitive gate-modulated photovoltaic effect is demonstrated, enabling the homojunction phototransistors at zero bias to deliver a photoresponsivity of 311 mA W^-1, a specific detectivity up to ~ 10¹¹ Jones, and an on/off ratio up to ~ 10⁴. Remarkably, when illuminated by the lights ranging from 405 to 808 nm, the biased devices yield a champion photoresponsivity of 191.5 A W^-1, a specific detectivity up to ~ 10¹² Jones, a photoconductive gain of 10⁶-10⁷, and a photoresponsive time in the order of ~ 50 ms. These results provide a simple and competitive solution to the bandgap engineering of two-dimensional materials for device applications without the need for p-n junctions.

Keywords: Graded bandgaps; Homojunctions; Phototransistors; Self-powered; Transition metal dichalcogenides.