Direct-indirect bandgap transition in monolayer MoS₂ induced by an individual Si nanoparticle

MoS₂ is promising for the next generation of electronic and optoelectronic devices by virtue of its unique optical, electrical and mechanical properties. Bandgap engineering of it is an interesting topic. However, the reported factors including temperature, defect, strain and external electric field are difficult to handle precisely. Here, we demonstrated direct-indirect bandgap transition in monolayer MoS₂ induced by an individual Si nanoparticle. We observed photoluminescence (PL) emission with obvious spectral redshift and broadening in the MoS₂/Si heterostructures after depositing Si nanoparticles onto the surface of monolayer MoS₂. Raman spectra of heterostructures show measurable shifts in contrast with the bare MoS₂. Energy transfer between MoS₂ and Si nanoparticles did not happen, which is demonstrated by scattering spectra of MoS₂/Si heterostructures. In addition, the natural oxide layer presented on the surface of Si nanoparticles can effectively prevent the carrier transferring from Si nanoparticles to MoS₂. Thus, we attribute the direct-indirect bandgap transition of monolayer MoS₂ to the strain induced by Si nanoparticles controlled by their sizes. The PL intensity of MoS₂/Si heterostructure depends on the size of Si nanoparticles, resulting from the enhanced optical absorption of monolayer MoS₂ based on Mie resonances of Si nanoparticles. The MoS₂/Si heterostructure is promising for photodetector and circuit integration.