Phase-Engineered Synthesis of Ultrathin Hexagonal and Monoclinic GaTe Flakes and Phase Transition Study

GaTe is an important III-VI semiconductor with direct bandgap; thus, it holds great potential in the field of optoelectronics. Although it is known that GaTe can exist both in monoclinic and hexagonal phases, current studies are still exclusively restricted to the monoclinic phase of two dimensional (2D) GaTe owing to the difficulty in the fabrication of 2D hexagonal GaTe. Both monoclinic and hexagonal GaTe are demonstrated in this work, which can be selectively synthesized via a physical vapor deposition method, under precisely controlled growth temperatures. The pristine Raman and non-linear optical properties of hexagonal GaTe has been systematically explored for the first time; moreover, a novel selected-area phase transition from hexagonal to monoclinic of GeTe has been achieved via fs-laser irradiation. This work may pave the way for widely use of 2D GaTe in various fields in future.