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Functional Inorganic Materials and Devices
Ultra-violet light induced persistent and degenerated doping in MoS for potential photo-controllable electronics applications 2
Rongjie Zhang, Zhijian Xie, Chunhua An, Shuangqing Fan, Qiankun Zhang, Sen Wu, Linyan Xu, Xiaodong Hu, Daihua Zhang, Dong Sun, Jianhao Chen, and Jing Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07196 • Publication Date (Web): 31 Jul 2018 Downloaded from http://pubs.acs.org on July 31, 2018
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ACS Applied Materials & Interfaces
Ultra-violet light induced persistent and degenerated doping in MoS2 for potential photo-controllable electronics applications 1 1
1
Rongjie Zhang, 2Zhijian Xie, 1Chunhua An, 1Shuangqing Fan, 1Qiankun Zhang, 1Sen Wu,
Linyan Xu, 1Xiaodong Hu, 1Daihua Zhang, 2,3Dong Sun, 2,3Jian-Hao Chen, and 1Jing Liu*
State Key Laboratory of Precision Measurement Technology and Instruments, School of Precision Instruments and Opto-electronics Engineering, Tianjin University, NO. 92 Weijin Road, Tianjin, China, 300072 2
International Center for Quantum Materials, School of Physics, Peking University, NO. 5 Yiheyuan Road, Beijing, China, 100871 3
Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
Corresponding author email:
[email protected] ACS Paragon Plus Environment
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Abstract Efficient modulation of carrier concentration is fundamentally important for tailoring the electronic and photoelectronic properties of semiconducting materials. Photo-induced doping is potentially a promising way to realize such a goal for atomically thin nanomaterials in a rapid and defect-free manner. However, the wide applications of photo-induced doping in nanomaterials are severely constrained by the low doping concentration and poor stability that can be reached. Here, we propose a novel photo-induced doping mechanism based on external photoelectric effect of metal coating on nanomaterials to significantly enhance the achievable doping concentration and stability. This approach is preliminarily demonstrated by the MX2 (M is Mo or Re, X is S or Se) nanoflake modified through a simple process of sequentially depositing and annealing an Au layer on the surface of the flake. Under ultra-violet (UV) light illumination, the modified MX2 achieves degenerated n-type doping density of 1014 cm-2 rapidly according to the experimentally observed >104 times increasement in the channel current. The doping level persists after the removal of UV illumination with non-observable decrease over 1 day in vacuum (less than 23% over 7 days under ambient environment). This photo-induced doping approach may contribute a major leap to the development of photo-controllable nano-electronics.
Key words: transition metal dichalcogenides, photo-induced doping, external photoelectric effect, gold coating, persistent photo current.
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ACS Applied Materials & Interfaces
Introduction Efficient modulation of carriers in semiconducting materials is the foundation to implement various functional electronic
1,2
and optoelectronic devices
3-5
. As the thickness of semiconducting
materials decreases to the atomic scale, the efficient carrier modulation not only becomes more critical but also confronts numerous unprecedented challenges. Transition metal dichalcogenides (TMDs), a major subgroup of the atomically thin two-dimensional materials family, mainly possess semiconducting properties, and thus, necessitate competent methods to modulate the carrier concentration to enable nano-scale van der Waals homo/heterojunctions and functional devices 6,7. Conventional doping technologies that are applicable to TMDs, such as substitution of transition metal by other elements 8-11, ion implantation
12
, and plasma treatment
13,14
, may alter and/or in-
troduce abundant defects to the intrinsic lattice structure, which diminishes the carrier mobility of TMDs. Other defect-free doping approaches reported recently are based on charge transfer between TMDs and gases 15,16, ions 17, nanoparticles 18, etc. These methods, however, usually suffer from long-term stability issue 19,20 and involve enduring solution-based processes, which are hardly compatible with standard CMOS processes. In contrast, photo-induced doping is considered to be an effective approach to provide rapid and defect-free doping 21-23. The working mechanism of photo-induced doping is generally based on the formation of electron-hole pairs in the photo-absorption layer under the photo illumination and subsequent charge transfer into the conduction channel 21, which modulates the carrier concentration of the target material without increasing the Coulombic scattering from space charges. In order to preserve the doping effect after the removal of photo illumination, a dielectric layer is usually applied above the conduction channel to introduce interface carrier trap-states 21,24 to prevent electron-hole recombination. In this mechanism, the number of carriers generated in the photon-absorption layer and the populated trap-states density largely determine the achievable doping concentration 21. Previous works mainly use dielectric and semiconducting materials as the photon-absorption layer, which usually generate limited number of carriers and very low doping concentration can be realized by this approach. In addition, the trap-states may gradually release the trapped carriers 25, leading to the decay of doping concentration after removal of photo illumination. Therefore, photo-induced doping method is rarely applicable due to the doping concentration
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