Phase Modulation of 2D Semiconducting GaTe from Hexagonal to Monoclinic through Layer Thickness Control and Strain Engineering

Phase engineering offers a novel approach to modulate the properties of materials for versatile applications. Two-dimensional (2D) GaTe, an emerging III-VI semiconductor, can exist in hexagonal (<i>h</i>) or monoclinic (<i>m</i>) phases with fascinating phase-dependent properties (e.g., isotropic or anisotropic electrical transport). However, the key factors governing GaTe phases remain obscure. Herein, we achieve phase modulation of GaTe by tuning two previously overlooked factors: layer thickness and strain. The precise layer-controlled synthesis of GaTe from a monolayer (1L) to >10L is achieved via molecular beam epitaxy. A layer-dependent phase transition from <i>h</i>-GaTe (1-5L) to <i>m</i>-GaTe (>10L) is unambiguously unveiled by scanning tunneling microscopy/spectroscopy, driven by system energy minimization according to density functional theory calculations. Local phase transitions from ultrathin <i>h</i>-GaTe to <i>m</i>-GaTe are also obtained via introduced tensile strain. This work clarifies the factors influencing GaTe phases, providing valuable guidance for the phase engineering of other 2D materials toward the desired properties and applications.