Oxygen-induced controllable p-type doping in 2D semiconductor transition metal dichalcogenides
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Oxygen-induced controllable p-type doping in 2D semiconductor transition metal dichalcogenides Qijie Liang1,2, Jian Gou2, Arramel2, Qian Zhang3 (), Wenjing Zhang1 (), and Andrew Thye Shen Wee2,4 () SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China 2 Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore 3 Department of Materials Science and Engineering, National University of Singapore, Singapore 117574, Singapore 4 Centre for Advanced 2D Materials, National University of Singapore, Block S14, 6 Science Drive 2, Singapore 117546, Singapore 1
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 15 July 2020 / Revised: 4 August 2020 / Accepted: 4 August 2020
ABSTRACT Exposure to oxygen alters the physical and chemical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs). In particular, oxygen in the ambient may influence the device stability of 2D TMDs over time. Engineering the doping of 2D TMDs, especially hole doping is highly desirable towards their device function. Herein, controllable oxygen-induced p-type doping in a range of hexagonal (MoTe2, WSe2, MoSe2 and PtSe2) and pentagonal (PdSe2) 2D TMDs are demonstrated. Scanning tunneling microscopy, electrical transport and X-ray photoelectron spectroscopy are used to probe the origin of oxygen-derived hole doping. Three mechanisms are postulated that contribute to the hole doping in 2D TMDs, namely charge transfer from absorbed oxygen molecules, surface oxides, and chalcogen atom substitution. This work provides insights into the doping effects of oxygen, enabling the engineering of 2D TMDs properties for nanoelectronic applications.
KEYWORDS two-dimensional, transition metal dichalcogenides, oxygen induced doping, oxygen substitution, charge transfer
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Introduction
There has been significant progress in two-dimensional (2D) materials research, among which transition metal dichalcogenides (TMDs) have received extensive attention owing to their unique electronic, optoelectronic, chemical and thermal properties [1–5]. The absence of surface dangling bonds of 2D TMDs makes them favorable candidates for high performance field-effect transistors (FETs) that are immune to the short-channel effect, a critical issue facing conventional bulk semiconductors. Due to their ultrathin nature and reduced screening relative to bulk systems, the properties and device performance of 2D TMDs are more sensitive to the environment [6–8]. In particular, oxygen in the ambient, also as a constituent of water and other molecules, plays a vital role in determining the optical and electronic properties, as well as the device performance and lifetime of 2D TMDs [9–13]. For example, oxygen molecules adsorbed at sulphur vacancies in M
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