Heteroepitaxial van der Waals semiconductor superlattices

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition metal dichalcogenide (TMDC) semiconductors offer diverse functionalities in monolayer (ML) form.
• Integration into van der Waals (vdW) superlattices (SLs) promises novel material structures.
• Achieving precise stacking of dissimilar MLs is crucial for exploring new properties.

Purpose of the Study:

• To report the atomic layer-by-layer epitaxial growth of vdW SLs with programmable stacking periodicities.
• To demonstrate the creation of vdW SLs using more than two kinds of dissimilar TMDC MLs.
• To achieve tunable 2D vdW electronic systems free of interlayer atomic mixing.

Main Methods:

• Kinetics-controlled vdW epitaxy in the near-equilibrium limit.
• Metal-organic chemical vapour deposition (MOCVD).
• Atomic layer-by-layer growth of MoS₂, WS₂, and WSe₂ MLs.

Main Results:

• Successfully grew vdW SLs with programmable stacking periodicities using multiple TMDC MLs.
• Achieved precise ML-by-ML stacking without interlayer atomic mixing.
• Demonstrated tunable 2D vdW electronic systems with type II band alignments.

Conclusions:

• The developed method enables the precise integration of diverse TMDC MLs into vdW SLs.
• Exploiting type II band alignments allows for the demonstration of valley-polarized carrier excitations.
• The observed valley-polarized carrier excitations scale with the number of stacked layers (n) in (MoS₂/WS₂)_n SLs.