WSe₂ Light-Emitting Tunneling Transistors with Enhanced Brightness at Room Temperature

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Monolayer transition metal dichalcogenides (TMDs) are direct bandgap semiconductors with potential for optoelectronics.
• Van der Waals heterostructures, like MoS2 between hexagonal boron nitride (hBN) and graphene, form light-emitting quantum wells (LEQWs).
• Existing MoS2 and MoSe2 LEQWs exhibit a significant drop in external quantum efficiency (EQE) from cryogenic to room temperatures.

Purpose of the Study:

• To compare the temperature-dependent performance of WSe2-based LEQWs with MoSe2-based LEQWs.
• To investigate the underlying physical mechanisms responsible for observed differences in EQE behavior.
• To explore the potential of WSe2 for high-performance room-temperature optoelectronic devices.

Main Methods:

• Fabrication of van der Waals heterostructures using WSe2 and MoSe2 monolayers.
• Characterization of light-emitting quantum wells (LEQWs) through photoluminescence spectroscopy.
• Temperature-dependent measurements of external quantum efficiency (EQE) from cryogenic to room temperature.

Main Results:

• WSe2 LEQWs demonstrate a remarkable increase in EQE with rising temperature, reaching 5% at room temperature.
• This room-temperature EQE in WSe2 is approximately 250 times higher than previously reported for MoS2 and MoSe2 LEQWs under ambient conditions.
• MoSe2 LEQWs exhibited a typical decrease in EQE with increasing temperature.

Conclusions:

• The distinct temperature dependence of WSe2 LEQWs is attributed to the inverted spin-orbit splitting of conduction band states compared to molybdenum dichalcogenides.
• This inverted splitting results in a dark lowest-energy exciton in WSe2, influencing its radiative recombination pathways.
• WSe2-based LEQWs present a promising platform for efficient room-temperature optoelectronic applications, overcoming limitations of current molybdenum-based systems.