Excitation-Dependent High-Lying Excitonic Exchange

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Monolayer transition metal dichalcogenides (TMDs) exhibit high light absorption and photoluminescence (PL), making them promising for optoelectronics.
• Interlayer charge transfer (CT) and energy transfer (ET) are key processes governing photocarrier relaxation in TMD heterostructures (HSs).
• Long-distance ET (tens of nm) is observed in TMDs, contrasting with the shorter-range CT process.

Purpose of the Study:

• To investigate the mechanisms of photocarrier relaxation in TMD heterostructures.
• To explore the role of interlayer hexagonal boron nitride (hBN) in mediating ET.
• To understand the influence of temperature on ET and PL emission.

Main Methods:

• Fabrication of WSe2/MoS2 heterostructures with an hBN interlayer.
• Photoluminescence (PL) spectroscopy to analyze emission characteristics.
• Temperature-dependent measurements to study the effect of electron-phonon scattering on ET.

Main Results:

• An efficient, long-distance ET from monolayer WSe2 to MoS2 was observed in the hBN-intercalated HS.
• The ET process is attributed to resonant overlapping of high-lying excitonic states between WSe2 and MoS2.
• Enhanced MoS2 PL emission was detected, demonstrating the effectiveness of the ET.
• Increasing temperature weakened the ET due to enhanced electron-phonon scattering, diminishing the MoS2 PL enhancement.

Conclusions:

• This work demonstrates an unconventional ET from a lower to higher optical bandgap material in TMD HSs.
• The findings provide new insights into long-distance ET mechanisms and their impact on photocarrier dynamics.
• The results highlight the potential for engineering ET pathways in TMD heterostructures for optoelectronic applications.