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 chalcogenide atomic orbits. This makes quantum confinement and interlayer interaction play a subtle role in two-dimensional (2D) monochalcogenides crystals. In this report, we study the direction-resolved photoluminescence of 2D Ga2Se2 at various thicknesses. We observe that the in-plane dipole radiation survives, but out-of-plane dipole radiation fades at 2D limits.