Broad band modulation of two-dimensional Mo1-x W x S2 by variational compositions

Abstract

Precisely tuning bandgap enables tailored design of materials, which is of crucial importance for optoelectronic devices. Towards this end, ternary Mo1-x W x S2 monolayers with continually variational transition metal compositions are synthesized by precisely control of the precursors and growth temperatures in the chemical vapor deposition process, and thus to manipulate the bandgap of the monolayers. Energy dispersive x-ray spectroscopy demonstrates that the composition of the ternary Mo1-x W x S2 monolayers can be effectively modulated by the precursors and synthesizing temperatures. Frequency and intensity of the Raman and photoluminescent peaks of the Mo1-x W x S2 monolayers are continually modulated by the variational Mo and W compositions. The maximum of 0.148 eV bandgap modulation is achieved by modulating the transition metal compositions, which is highly consistent to the calculated 0.158 eV by first-principles theory. Photodetectors based on the Mo1-x W x S2 monolayers are fabricated and U-shape of photoresponse characteristics are demonstrated as x change from 0 to 1 under the same measurement conditions. The estimated photocurrent, photoresponsivity and external quantum efficiency show that the minimum values appear at the composition of x = 0.5, while the maximum values appear at x = 1. The results illustrate an excellent level of control on the band structure of two-dimensional ternary Mo1-x W x S2 by precisely control of the transition metal compositions.