Quantitative Thermal Characterization of Supported and Encapsulated 2D Semiconductors

Heat conduction in two-dimensional (2D) materials differs from their bulk counterparts due to the role of interfaces and microstructural defects, geometry-dependent phonon band structure, and phonon scattering at phase boundaries. For example, 2D semiconductors are placed in contact with dielectric gates and metal source and drain electrodes in practical applications, leading to significantly reduced thermal conductivity due to phonon scattering with the substrate and superstrate. Studies of the thermal conductivity of substrate-supported and encapsulated 2D materials are critical for managing heat dissipation in 2D field-effect transistors. This work reports the in-plane and cross-plane thermal conductivity measurements in MoS₂ and CrI₃ nanosheets, based on the combination of the frequency domain thermoreflectance (FDTR) and optothermal Raman spectroscopy (OTRS) techniques. Combining the two techniques overcomes the limitations of the individual methods by decoupling the in-plane and through-thickness thermal property measurements. We will show that this new measurement approach is suitable for quantitative characterization of the anisotropic thermal conductivity and thermal boundary conductance of supported and encapsulated quasi-2D and few-layer semiconducting films.