Dipole Orientation Shift of Ga₂Se₂ by Quantum Confinement

In the family of III-VI monochalcogenides M₂X₂ (M = Gallium, Indium; X = Sulfur, Selenide, etc), the interlayer interaction and the electronic band edges share the contribution of the same chalcognide atomic orbits. This makes quantum confinement and interlayer interaction play a subtle role in 2 dimensional (2D) monochalcogenides crystals. In this report we study the direction-resolved photoluminescence of 2D Ga₂Se₂ at various thickness. We observe that the in-plane dipole radiation survives but out-of-plane dipole radiation fades at 2D limit.