Layer-dependent dielectric modulation in WS2/GaN heterostructures

Controlling over the electronic structure of two-dimensional (2D) semiconductors is crucial to unlock their full potential in the applications in future nanodevices. Here, we demonstrate a layer-dependent dielectric modulation of electronic structures in multilayer ${\mathrm{WS}}_{2}/\mathrm{GaN}$ heterostructures. The results investigated by means of in situ scanning tunneling microscopy/spectroscopy and photoluminescence spectroscopy show that the fluctuations of the dielectric environment induced by local corrugation of the GaN surface dramatically tune the band structure of monolayer ${\mathrm{WS}}_{2}$ with a large downshift of the valence band maximum by about 1.12 eV. Under the shielding effect of the first-layer ${\mathrm{WS}}_{2}$, the dielectric environment shows a weak modulation effect on the second-layer, and even has negligible influence on the third- and fourth-layer ${\mathrm{WS}}_{2}$. The relationship between dielectric environment and interfacial distance is further simulated through first-principles calculations. The electrostatic potential energy, differential charge densities, and charge transfer of the ${\mathrm{WS}}_{2}/\mathrm{GaN}$ heterostructure under different interfacial distances reveal that the differences of charge redistributions between the ${\mathrm{WS}}_{2}/\mathrm{GaN}$ interface and ${\mathrm{WS}}_{2}$ interlayer are responsible for the layer-dependent dielectric modulation. This work offers some references for the design and fabrication of novel 2D optoelectronic devices.