Substrate induced infrared carrier scattering in graphene

초록

The infrared (IR) optical response of graphene is governed by free-carrier dynamics that are strongly influenced by the surrounding dielectric environment. Although graphene has been extensively studied at visible and near-IR frequencies, the temperature evolution of its IR carrier dynamics remains largely unexplored. Here we investigate monolayer graphene on SiO 2/Si and hexagonal boron nitride (hBN)/SiO 2/Si using temperature-dependent IR spectroscopic ellipsometry between 4 K and 300 K. From Drude analysis of the ellipsometric spectra, we extract the complex dielectric function and key transport parameters of the IR free carriers. In contrast to the behavior typically observed in dc transport, the optically derived resistivity decreases with increasing temperature for both substrates. Despite comparable carrier densities, graphene on hBN exhibits systematically reduced scattering rates and a stronger temperature evolution of the IR Drude response compared with graphene on SiO 2. These results reveal that substrate-induced scattering plays a dominant role in determining the IR carrier dynamics of graphene, particularly at low temperatures where intrinsic phonon scattering is suppressed. Our work establishes IRSE as a powerful contact-free probe of carrier transport in two-dimensional materials and highlights the importance of dielectric-environment engineering for low-loss graphene-based IR photonic devices.

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