Morphological dependent exciton dynamics and thermal transport in MoSe₂ films

Thermal transport and exciton dynamics of semiconducting transition metal dichalcogenides (TMDCs) play an immense role in next-generation electronic, photonic, and thermoelectric devices. In this work, we synthesize distinct morphologies (snow-like and hexagonal) of a trilayer MoSe₂ film over the SiO₂/Si substrate via the chemical vapor deposition (CVD) method and investigated their morphological dependent exciton dynamics and thermal transport behaviour for the first time to the best of our knowledge. Firstly, we studied the role of spin-orbit and interlayer couplings both theoretically as well as experimentally via first-principles density functional theory and photoluminescence study, respectively. Further, we demonstrate morphological dependent thermal sensitive exciton response at low temperatures (93-300 K), showing more dominant defect-bound excitons (E_L) in snow-like MoSe₂ compared to hexagonal morphology. We also examined the morphological-dependent phonon confinement and thermal transport behaviour using the optothermal Raman spectroscopy technique. To provide insights into the nonlinear temperature-dependent phonon anharmonicity, a semi-quantitative model comprising volume and temperature effects was used, divulging the dominance of three-phonon (four-phonon) scattering processes for thermal transport in hexagonal (snow-like) MoSe₂. The morphological impact on thermal conductivity (k_s) of MoSe₂ has also been examined here by performing the optothermal Raman spectroscopy, showing k_s ∼ 36 ± 6 W m^-1 K^-1 for snow-like and ∼41 ± 7 W m^-1 K^-1 for hexagonal MoSe₂. Our research will contribute to the understanding of thermal transport behaviour in different morphologies of semiconducting MoSe₂, finding suitability for next-generation optoelectronic devices.