Excitons in 2D materials

The band structure in a semiconductor features a top valence band and the lowest conduction band.

The energy difference between these bands is the bandgap.

When shining light with energy larger than the bandgap, the electrons in the valence band are pumped up to the conduction band and leave holes in the valence band.

Electrons like to meet up with holes and form excitons!

The characteristic of the exciton is determined by the properties of the electron and the hole.

Electrons and holes can come from various sources and thus behave differently.

In some materials, the exciton is bright. While in some materials, the exciton is likely to be dark.

In artificial 2D materials, the brightness of the excitons is tunable.