Air stable p-doping of WSe2 by covalent functionalization

Area of Science:

• Materials Science
• Solid State Physics
• Surface Chemistry

Background:

• Transition metal dichalcogenides (TMDCs) are promising 2D materials with tunable electronic properties.
• Achieving stable chemical doping in TMDCs, particularly for air-stable p-doping, remains a significant challenge.
• Contact resistance is a critical bottleneck for TMDC-based electronic devices.

Purpose of the Study:

• To investigate covalent functionalization as a method for air-stable chemical doping of TMDCs.
• To explore the p-doping of tungsten diselenide (WSe2) using nitrogen oxide (NOx) chemisorption.
• To demonstrate the impact of doping on the electrical properties and contact resistance of WSe2.

Main Methods:

• Chemisorption of NOx on WSe2 at 150 °C.
• Synchrotron-based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) for chemical state analysis.
• Ab initio simulations to identify favorable dopant species and configurations.
• Electrical measurements to quantify hole concentration and contact resistance.

Main Results:

• Formation of WSe(2-x-y)O(x)N(y) species on WSe2 surfaces and interfaces via NOx chemisorption.
• Identification of WSe2:NO at selenium vacancy sites as the predominant dopant species through spectroscopy and simulations.
• Achieved a maximum hole concentration of ~10^19 cm^-3, independent of WSe2 thickness.
• Demonstrated a 5-order-of-magnitude reduction in contact resistance between Pd and WSe2.

Conclusions:

• Covalent functionalization offers a viable route for air-stable chemical doping of TMDCs.
• NOx chemisorption effectively p-dopes WSe2, leading to degenerate semiconductor characteristics.
• The developed doping strategy significantly improves contact properties, paving the way for advanced TMDC electronics.