Ultrafast Exciton Dynamics in Few-Layer MoTe₂ near the Direct-Indirect Bandgap Transition

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition metal dichalcogenides (TMDs) are explored for optoelectronics and quantum computing.
• The 2H semiconducting phase of molybdenum ditelluride (MoTe2) is promising for optical devices.
• Photophysics of ultrathin MoTe2 films near the direct-to-indirect bandgap transition are underexplored.

Purpose of the Study:

• Investigate charge carrier kinetics in ultrathin MoTe2 films.
• Quantify the influence of film thickness on photophysics.
• Understand carrier decay mechanisms in relation to defect states.

Main Methods:

• Fabrication of ultrathin MoTe2 using atomic layer deposition (ALD) and chemical vapor deposition (CVD).
• Time-resolved optical spectroscopy to analyze charge carrier dynamics.
• Examination of samples with thicknesses from monolayers to bilayers.

Main Results:

• A proposed mechanism involves fast relaxation and excitonic state formation.
• Excitonic decay occurs via bulk and surface defect trap states.
• Surface trapping decay rate decreases with increasing film thickness.

Conclusions:

• Both bulk and surface defect states significantly impact MoTe2 carrier lifetimes.
• Controlling interface defect states is critical for heterojunction optical devices.
• Understanding carrier dynamics is essential for MoTe2-based device implementation.