Interference‐Enhanced Broadband Absorption of Monolayer MoS 2 on Sub‐100 nm Thick SiO 2 /Si Substrates: Reflection and Transmission Phase Changes at Interfaces

The optical characteristics of MoS 2 monolayers on SiO 2 /Si substrates with an SiO 2 thickness ranging from 40 to 130 nm are investigated. The measured Raman and optical reflection spectra of the MoS 2 monolayers vary considerably depending on the SiO 2 thickness. The Raman peak intensity of the MoS 2 monolayer on the substrate with an 80 nm thick SiO 2 layer is four times larger than those in the cases of 40‐ and 130 nm thick SiO 2 layers, indicating a significant difference in the absorption at the excitation wavelength. The incident light undergoes anomalous phase changes upon reflection and transmission at the highly absorbing MoS 2 /nonabsorbing SiO 2 or air interfaces. The phase changes at these interfaces in conjunction with those induced by the propagation of light in the SiO 2 layer cause complex interference, which dramatically tunes the absorption spectrum of the MoS 2 layer with changing SiO 2 thickness. Neither wavelength nor the incident angle of light strongly affects the interface phase change. Thus, the MoS 2 monolayers on sub‐100 nm thick SiO 2 /Si substrates exhibit broadband omnidirectional absorption in the visible range. This work demonstrates that SiO 2 /Si wafers, which are the most popular substrates, allow the optical responses of MoS 2 monolayers to be optimized for optoelectronic applications.