Direct-Bandgap Bilayer WSe₂ /Microsphere Monolithic Cavity for Low-Threshold Lasing

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Monolayer transition metal dichalcogenides (TMDs) are promising 2D gain materials for light sources due to their direct bandgap and high photoluminescence quantum yield.
• However, monolayer TMDs exhibit weak emission and material degradation issues, limiting their integration into optical cavities.
• Existing 2D gain media face challenges in achieving efficient light emission and stable device performance.

Purpose of the Study:

• To develop a high-quality monolithic structure using bilayer tungsten diselenide (WSe2) on silica microsphere (MS) cavities.
• To enhance the photoluminescence intensity and optical confinement factor of WSe2 gain materials.
• To realize an ultralow threshold microlaser based on the novel WSe2/MS platform.

Main Methods:

• Directly growing single-domain WSe2 bilayers on single silica microsphere cavities.
• Utilizing the completely wrapped structure to induce an indirect-to-direct bandgap transition in WSe2 bilayers.
• Fabricating and characterizing the bilayer WSe2/MS microlaser device.

Main Results:

• Achieved a 60-fold increase in photoluminescence intensity due to the guided bandgap transition.
• Enhanced the optical confinement factor by over 20-fold through the monolithic structure.
• Realized a microlaser with an ultralow threshold of 0.72 W cm⁻², significantly lower than previous records.

Conclusions:

• Multilayer TMD materials can serve as effective 2D gain media for advanced light sources.
• The monolithic WSe2/MS platform offers a promising route for developing ultracompact and high-performance lasing devices.
• This study opens new avenues for integrated optoelectronics and photonic devices.