Atomic Layer MoSTe Ternary Alloys: Two-Dimensional van der Waals Growth, Band gap Engineering, and Electrical Transport.

Ternary alloys in two-dimensional (2D) transition-metal dichalcogenides allow band gap tuning and phase engineering and change the electrical transport type. A process of 2D van der Waals epitaxial growth of molybdenum sulfide telluride alloys (MoSTe, 0 ≤ ≤ 1) is presented for synthesizing few-atomic-layer films on SiO substrates using metal-organic chemical vapor deposition. Raman spectra, X-ray photoelectron spectra, photoluminescence (PL), and electrical transport properties of few-atomic-layer MoSTe (0 ≤ ≤ 1) films are systematically investigated. The strong PL peaks at 80 K from MoSTe (0.45 ≤ ≤ 0.93) reveal a composition-controllable optical band gap ( = 1.55-1.91 eV at 80 K). Electrical transport properties of MoSTe alloys, where 0 ≤ ≤ 0.8 and 0.93 ≤ ≤ 1, exhibit p-type and n-type semiconducting behaviors, respectively. Remarkably, an increase in the Te composition of a few-atomic-layer MoSTe (0 ≤ ≤ 1) film left-shifts the threshold voltage of a MoSTe (0 ≤ ≤ 1) field-effect transistor. The narrower band gap energies of MoSTe films with higher Te content cause a decrease in the on/off current ratios.