Carbon doping of WS2 monolayers: Bandgap reduction and p-type doping transport

Fu Zhang; Yanfu Lu; Daniel S Schulman; Tianyi Zhang; Kazunori Fujisawa; Zhong Lin; Yu Lei; Ana Laura Elias; Saptarshi Das; Susan B Sinnott; Mauricio Terrones

doi:10.1126/sciadv.aav5003

Carbon doping of WS₂ monolayers: Bandgap reduction and p-type doping transport

Sci Adv. 2019 May 24;5(5):eaav5003. doi: 10.1126/sciadv.aav5003. eCollection 2019 May.

Authors

Fu Zhang^{1

2}, Yanfu Lu¹, Daniel S Schulman¹, Tianyi Zhang^{1

2}, Kazunori Fujisawa^{2

3}, Zhong Lin^{2

3}, Yu Lei¹, Ana Laura Elias^{2

3}, Saptarshi Das^{2

4}, Susan B Sinnott^{1

2

5}, Mauricio Terrones^{1

2

3

5}

Affiliations

¹ Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
² Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA.
³ Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA.
⁴ Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA 16802, USA.
⁵ Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA.

Abstract

Chemical doping constitutes an effective route to alter the electronic, chemical, and optical properties of two-dimensional transition metal dichalcogenides (2D-TMDs). We used a plasma-assisted method to introduce carbon-hydrogen (CH) units into WS₂ monolayers. We found CH-groups to be the most stable dopant to introduce carbon into WS₂, which led to a reduction of the optical bandgap from 1.98 to 1.83 eV, as revealed by photoluminescence spectroscopy. Aberration corrected high-resolution scanning transmission electron microscopy (AC-HRSTEM) observations in conjunction with first-principle calculations confirm that CH-groups incorporate into S vacancies within WS₂. According to our electronic transport measurements, undoped WS₂ exhibits a unipolar n-type conduction. Nevertheless, the CH-WS₂ monolayers show the emergence of a p-branch and gradually become entirely p-type, as the carbon doping level increases. Therefore, CH-groups embedded into the WS₂ lattice tailor its electronic and optical characteristics. This route could be used to dope other 2D-TMDs for more efficient electronic devices.