Equal-Bilayer MoSe₂ Grown by a Nucleation-Etching Strategy with High Carrier Mobility

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Bilayer transition metal dichalcogenides (TMDs) offer enhanced properties over monolayers, but uniform synthesis remains a challenge.
• Non-uniform bilayers lead to Schottky barriers, hindering carrier mobility and device performance.
• Controlling layer number uniformity is critical for predictable physical properties in TMDs.

Purpose of the Study:

• To develop a novel strategy for synthesizing uniform equal-bilayer (EB) molybdenum diselenide (MoSe2).
• To overcome the limitations of traditional layer-by-layer synthesis methods for bilayer TMDs.
• To improve the carrier mobility of MoSe2-based transistors by optimizing bilayer structure and metal contact.

Main Methods:

• Utilized a chemical vapor deposition (CVD) technique incorporating a nucleation-etching strategy.
• Controlled preferential second layer formation beneath the first layer.
• Observed preferential etching at overlapping grain boundary sites on the top layer.

Main Results:

• Successfully synthesized uniform equal-bilayer (EB) MoSe2 with 3R-stacking and high crystal quality.
• Achieved significantly improved metal contact with EB-MoSe2 compared to unequal bilayers.
• EB-MoSe2 transistors demonstrated an order of magnitude higher carrier mobility (104 cm^2 V^-1 s^-1) than UEB-MoSe2 transistors (12 cm^2 V^-1 s^-1).

Conclusions:

• The nucleation-etching strategy is a feasible method for synthesizing high-quality EB-TMDs.
• This approach effectively enhances carrier mobility in MoSe2 transistors.
• The findings are significant for the development of high-performance 2D optoelectronic devices.