2H/1T′ phase WS2(1−x)Te2x alloys grown by chemical vapor deposition with tunable band structures

Abstract

Two-dimensional (2D) transition-metal tellurides have recently emerged as a nontrivial material for novel physical properties. Alloying tellurium with other 2D sulfides/selenides will give rise to new interesting phenomena and find broad opportunities in device applications. However, the growth of Te-based alloys to date is largely limited. Here, we demonstrate a chemical vapour deposition (CVD) method to synthesize monolayer WS2(1−x)Te2x alloys with a wide range of Te composition (x = 0–1.0) via modulating the concentration of hydrogen gas. The substitutional Te-doping at chalcogen sites would lead to a structural phase transition from semiconducting 2H to semimetallic 1T′ phase at high Te ratio (≥50%). Accordingly, the optical band gaps of the alloys have redshifted from 1.97 to 1.67 eV in 2H phase and directly quenched in 1T′ phase. Besides, Te dopants were microscopically observed a random distribution within 2H structure, while S atoms displayed the anisotropic ordering in 1T′ phase. This alloy engineering can also effectively modulate the conductivity behavior of devices. Our work provides a facile method to control the composition and phase in alloying process, which expands the library of 2D materials and inspires the fundamental studies for nanoelectronics and nanophotonics applications.