Controllable Doping Characteristics for WS_xSe_y Monolayers Based on the Tunable S/Se Ratio

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition metal dichalcogenides (TMDs) are 2D materials with unique electronic properties and potential for device applications.
• Previous research has focused on synthesizing various TMD monolayers, but doping behavior remains less explored.
• Tungsten chalcogenide (WS_xSe_y) monolayers offer tunable electronic properties.

Purpose of the Study:

• To investigate the doping behavior of WS_xSe_y monolayers synthesized via chemical vapor deposition (CVD).
• To control the sulfur (S) to selenium (Se) ratio in WS_xSe_y monolayers and observe its effect on electronic properties.
• To explore the tunability of the optical band gap in WS_xSe_y monolayers.

Main Methods:

• Synthesis of WS_xSe_y monolayers using the CVD process.
• Controlled variation of the S:Se ratio by adjusting sulfur powder heating temperatures.
• Characterization of electronic states using energy band diagrams.
• Analysis of doping behavior through Raman spectroscopy (observing peak shifts).

Main Results:

• Increasing the Se component induced a transition from p-type to n-type behavior in WS_xSe_y monolayers.
• Enhanced S component led to clearer p-type characteristics.
• Raman spectra showed red shifts (WS₂-related peaks) indicating n-doping and blue shifts (WSe₂-related peaks) indicating p-doping.
• The optical band gap was precisely tunable from 1.97 eV to 1.61 eV.

Conclusions:

• The S:Se ratio in WS_xSe_y monolayers is a critical factor in determining their doping type (n-type or p-type).
• Raman spectroscopy effectively probes the doping behavior of these 2D materials.
• Tunable doping and band gap offer significant design flexibility for future electronic and optical devices.