Probing interlayer excitons in a vertical van der Waals p-n junction using a scanning probe microscopy technique

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) semiconductors exhibit unique optoelectronic properties due to quantum confinement.
• Interlayer excitons in van der Waals (vdW) heterostructures are crucial for advanced electronic applications.

Purpose of the Study:

• To investigate interlayer excitons in a vertical p-n junction of n-type MoS2 and p-type GaSe.
• To explore the potential of these heterostructures for optoelectronics and light harvesting.

Main Methods:

• Fabrication of a MoS2/GaSe vdW heterostructure on highly ordered pyrolytic graphite (HOPG) as a bottom contact.
• Characterization using current sensing atomic force microscopy (CSAFM) with home-built Au tips.
• Electrical measurements including diode characterization and photocurrent mapping.
• Theoretical validation using density functional theory (DFT) and experimental confirmation via photoluminescence (PL) spectroscopy.

Main Results:

• The MoS2/GaSe p-n junction exhibited strong rectification (10^4 at ±1 V) and photovoltaic effects (fill factor 0.55).
• DFT calculations predicted an interface-specific state at 1.5 eV, confirmed by PL measurements showing excitonic transitions.
• Photocurrent mapping demonstrated efficient extraction of excitons under 785 nm excitation.

Conclusions:

• The study successfully demonstrates the formation and efficient extraction of interlayer excitons in a MoS2/GaSe vdW heterostructure.
• This work presents a viable pathway for developing next-generation 2D optoelectronic devices and light harvesters.