Layer-dependent Charge Transfer and inter-layer coupling in WSe2/Graphene Heterostructures
Abstract
Understanding interfacial interactions in two-dimensional (2D) heterostructures is essential for advancing optoelectronic and quantum technologies. We investigate metal-organic chemical vapor deposition (MOCVD)-grown WSe2 films (one to five layers) on graphene/SiC, directly compared to exfoliated WSe2 on SiO2, using Raman and photoluminescence (PL) spectroscopy complemented by atomic force microscopy (AFM). Raman measurements reveal compressive strain and interfacial charge transfer in WSe2/graphene heterostructures, evidenced by blue-shifted phonon modes and the emergence of higher-order interlayer breathing modes absent on SiO2. Concomitant shifts and attenuation of graphene's G and 2D modes with increasing WSe2 thickness indicate progressive p-type doping of graphene, while WSe2 phonon shifts point to n-type doping of the semiconductor, consistent with interfacial electron transfer. PL shows strong quenching for monolayer WSe2 on graphene due to ultrafast charge transfer and F"orster resonance energy transfer (FRET), with partial emission recovery in multilayers relative to SiO2-supported flakes. Exciton behavior differs strongly between substrates: on SiO2, A- and B-exciton energies vary markedly with thickness, whereas on graphene they remain nearly pinned. This stability reflects the combined effects of graphene's strong dielectric screening and charge-transfer-induced free-carrier screening, with strain playing a secondary role. These results establish graphene, unlike SiO2, as an active interfacial partner that stabilizes excitonic states and enables engineering of the optical response of 2D heterostructures.
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