Optical absorption in 2D MoS₂ monolayers conformally grown on 3D Si and SiO₂ nanocone arrays

We prepared 2D MoS₂ monolayers conformally coated on Si and SiO₂ nanocone (NC) arrays using metal organic chemical vapor deposition technique, and investigated the influences of the refractive indices of 3D NCs on the optical properties of 2D MoS₂ monolayers. The height, bottom diameter, and the period of the hexagonal Si NC array were 460, 250, and 300 nm, respectively. The SiO₂ NC array was prepared by thermal oxidation of the Si NC array. The photoluminescence and Raman intensities of the MoS₂ monolayer on the SiO₂ NC were higher than those on the Si NC, although the Si NC exhibited much lower optical reflectivity in the visible wavelength range compared with the SiO₂ NC. Numerical calculations showed that the strongly confined light in the high refractive index Si NC prevented a large electric field formation at the NC surface. In contrast, the weak light confinement in the low refractive index SiO₂ NC resulted in a large electric field intensity and enhanced absorption in the MoS₂ monolayer on the SiO₂ NC. This work demonstrates that the 2D MoS₂ and 3D Si hybrid nanostructures can provide a useful means to realize high-performance optoelectronic devices.