Broadband Optical Properties of Few-layer Large-area MoS₂

We combined broadband optical spectroscopy with first-principles calculations and band-nesting analysis to investigate the optical properties of few-layer large-area MoS₂ (4, 6, 8, and 18L) deposited on quartz substrates. The real and imaginary part of the dielectric function was investigated covering infra-red, visible, and ultraviolet energies (0.8-6.5 eV) using Transmittance spectroscopy. We have assigned the prominent optical transitions in the high energy range between 3-6 eV, namely the D and E transitions, with strong inter-band transitions. The D peak at 3.0 eV is revealed in thicker many-layer films, and the E peak at 4.5 eV is observed for all thicknesses. Comparing with theory results, we identified and assigned the E peak in the dielectric function at 4.5 eV to Γ to Γ transitions in the band structure from Mo-xy to S-p_x orbitals. Another inference during our comparative studies is that A,B peaks are excitonic, C is mixed with excitonic and non-excitonic interband transitions, and D and E are entirely due to interband transitions. Finally, we will present band-nesting analysis to understand why the electronic structure of few-layer MoS₂ supports strong light-matter interactions leading to the high dielectric constants at the few-layer level.