InSe as a case between 3D and 2D layered crystals for excitons

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Indium selenide (InSe) is recognized for its potential in optoelectronic applications.
• The behavior of excitons significantly influences InSe's properties.
• Previous studies accepted a lower exciton binding energy for InSe.

Purpose of the Study:

• To investigate the luminescence properties of InSe under varying excitation power.
• To re-evaluate the exciton binding energy in InSe using P-band analysis.
• To explore the dimensionality and parameters of excitons in InSe.

Main Methods:

• Photoluminescence spectroscopy to observe exciton, biexciton, and P-band emissions.
• Analysis of energy and momentum conservation rules for the P-band.
• Theoretical calculations incorporating anisotropic material parameters.

Main Results:

• Observed sequential luminescence of exciton, biexciton, and P-band with increasing excitation power.
• Determined a revised exciton binding energy of ≥20 meV, higher than the previously accepted 14 meV.
• Identified a peak near the bandgap (~1.36 eV) influenced by the Sommerfeld factor.
• Theoretical calculations suggest a deviation from the pure three-dimensional exciton model in InSe.

Conclusions:

• The revised exciton binding energy is consistent with the robustness of excitons in InSe up to room temperature.
• Findings challenge the assumption of a purely three-dimensional exciton character in InSe.
• Accurate exciton characterization is vital for advancing InSe in nanophotonics.