Disentangling Light-Induced Charge Transfer, Heating, and Strain Effects in WS2/Graphene Heterostructures

Heterostructures formed by 2D transition metal dichalcogenides (TMDCs) and graphene are not only fundamentally important for the exploration of novel interface physics but also indispensable for various optoelectronic devices. Often multiple effects such as charge transfer (CT), heating, and strain are present simultaneously and their interplay significantly impacts the properties of such heterostructures. However, the identification and separation of these three individual effects are challenging and have not been demonstrated in 2D heterostructures. Here, through a concurrent analysis of the Raman modes and photoluminescence spectra from graphene and WS2 in temperature- and power-dependent measurements, this work has succeeded in disentangling the effects of light-induced CT, heating, and strain effects in WS2/graphene heterostructure on SiO2/Si substrate. Without disentangling these effects, the light-induced carrier density in graphene (WS2) would have been underestimated (overestimated) by up to 62% (73%) in this situation. More importantly, a positive temperature coefficient of the G-mode Raman shift is obtained without excluding the strain and CT effects, contrary to the negative coefficient due to the intrinsic thermal effect. This study demonstrates the importance of disentangling the individual effects and the approach paves the way for a comprehensive understanding of electrical, thermal, and mechanical properties of TMDC/graphene heterostrucutres.