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

## TL;DR

This paper investigates the excitonic properties of indium selenide (InSe), revealing a higher exciton binding energy than previously thought and questioning its assumed 3D nature, with implications for nanophotonics.

## Contribution

It provides a revised exciton binding energy for InSe and challenges the assumption of its purely three-dimensional excitonic character.

## Key findings

- Exciton binding energy is at least 20 meV, higher than the accepted 14 meV.
- Observation of exciton, biexciton, and P band with increasing excitation power.
- Evidence of a near bandgap peak suggests non-3D excitonic behavior.

## Abstract

We demonstrate the successive appearance of the exciton, biexciton, and P band of the exciton-exciton scattering with increasing excitation power in the photoluminescence of indium selenide layered crystals. The strict energy and momentum conservation rules of the P band are used to reexamine the exciton binding energy. The new value $\geq 20$ meV is markedly higher than the currently accepted 14 meV, being however well consistent with the robustness of excitons up to room temperature. A peak controlled by the Sommerfeld factor is found near the bandgap ($\sim 1.36$ eV), which puts the question on the pure three-dimensional character of the exciton in InSe, which has been assumed up to now. Our findings are of paramount importance for the successful application of InSe in nanophotonics.