Layer thickness-dependent optical properties of GaTe

Gallium Telluride (GaTe) has emerged as a potential candidate for optoelectronic applications due to its outstanding optical properties. However, a comprehensive understanding of the thickness-dependent optical properties, particularly the bandgap and vibration modes, is still lacking. In this study, we investigated the dependence of bandgap and Raman-active modes on layer thickness by measuring micro-photoluminescence (PL) and micro-Raman spectroscopy of GaTe at 77 K. Our results revealed a significant dependence of bandgap and Raman-active modes on layer thickness, with the bandgap of GaTe flakes increasing from 1.736 to 2.09 eV as the thickness decreases from bulk to 1.5 nm. Furthermore, the quantum confinement effect led to a direct to indirect bandgap transition in few-layered GaTe. We also interpret interlayer coupling and long-range Coulomb interactions between layers resulted in the appearance of an extra Raman peak associated with the shear or breathing modes and structural change for GaTe-flakes with decreasing their thickness down to a few layers. Additionally, we observed a softening of A3g , A4g , and A5g modes and stiffening of others with reducing thickness. Our results provide a comprehensive understanding of the thickness dependence of optical properties in GaTe material.