AVS 63rd International Symposium & Exhibition
    2D Materials Focus Topic Thursday Sessions
       Session 2D-ThA

Paper 2D-ThA8
Passivation of Transition Metal Chalcogenide Surface via Sulfur Layer to Enhanced Metal Contact

Thursday, November 10, 2016, 4:40 pm, Room 103B

Session: Surface Chemistry, Functionalization, Bio and Sensor Applications of 2D Materials
Presenter: JunHong Park, Univeristy of California, San Diego
Authors: J.H. Park, Univeristy of California, San Diego
A. Rai, University of Texas at Austin
I.J. Kwak, Univeristy of California, San Diego
S. Bhattacharjee, Indian Institute of Science, Bangalore
K. Ganapathi, Indian Institute of Science, Bangalore
N. Bhat, Indian Institute of Science, Bangalore
S.K. Banerjee, University of Texas at Austin
A.C. Kummel, University of California, San Diego
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The performance of FETs based on transition metal chalcogenide (TMD) is limited by the contact resistance between metal and TMD channels, resulting from the interface degradation during metal deposition on TMDs, metal reaction at defect sites or work function differences between TMDs and metals. In this presentation, the amorphous sulfur layers are formed on MoS2 to protect the surface of MoS2 during metal deposition and form an interfacial layer between MoS2 and metal. The MoS2 (bulk) flake is emerged into ammonium sulfide 40 % (NH4)2S in H2O at 523 K (technique of Karr et al). Afterwards, the sulfur treated MoS2 (bulk) is transferred into a UHV chamber to observe the atomic and electronic transformations of the surface via scanning tunneling microscopy (STM) and spectroscopy (STS). In the STM and STS, the sulfur-treated surface band gap is measured 1.85 ± 0.03 eV, while the bare MoS2 bulk has 1.27 ± 0.02 eV band gap, consistent with existence of sulfur layer on MoS2. Annealing the sample at 623 K for 60 mins results an increase in the band gap to 2.30 ± 0.03 eV. Additional annealing at 793 K of sulfur treated MoS2 results in observation of crystalline sulfur clusters on MoS2. However, this sulfur layer can be desorbed from MoS2 by just direct hearing to 793 K for 1 hr without intermediate step, Afterward, no missing sulfur atoms are observed nor any surface residues; however, there are sulfur clusters inside of the large native defects. The amorphous sulfur layer can be used as interface control for contact deposition. The MoS2 devices were fabricated to elucidate the impact of sulfur treatments on MoS2 FETs. After sulfur treatment of multilayer MoS2, the metal contacts are defined by electron beam lithography and deposition, afterwards the samples were annealed at 673 K for 15 mins. In the electronic measurements, the contact resistance of multilayer MoS2 and metal decrease to half of non-treated MoS2 FET. The present sulfur treatment can expand to other TMD materials to improve the contact of TMDs and metal by providing both defect passivation and an interfacial control monolayer to prevent TMDA reaction and an ultrathin metal-sulfide interfacial control layer.