Effects of substrates on the optical properties of monolayer WS2

Abstract

Two-dimensional (2D) transition-metal dichalcogenides such as WS2 have attracted an increasing attention in recent years due to their potentials in electronic and optical applications. It is well known that the properties of these 2D systems are sensitive to their surroundings especially substrates. In this paper, we have investigated the effects of sapphire and SiO2/Si substrates on the optical properties of monolayer WS2 using temperature-dependent Raman spectrum, power-dependent and time-resolved photoluminescence (PL). The related results demonstrate substrates exert profound impacts on the Raman and PL properties of WS2. In comparison with the WS2/sapphire sample, charge doping effect contributes to the higher first-order temperature coefficient of A1g mode and larger trion binding energy obtained in the WS2/SiO2/Si sample. Both deduced decay times τ0 and τ1of the WS2/sapphire sample, which correspond to the lifetime of trions and excitons, respectively, are much larger than those of the WS2/SiO2/Si sample. The exploration of the nonlinear optical properties of monolayer WS2 on different substrates provides significant guidance for future device design since the related devices will be used under various surroundings and excitation power density.