Influence of band offset, nanostructuring, and applied electric field on the optoelectronic properties of vertically stacked MoS2/WS2 materials

Abstract

We theoretically investigate the electronic and optical properties of multilayer vertically stacked ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$ heterostructures, focusing on the role of the ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ band offset, number of monolayers in the heterostructure, effects of an applied electric field, and size reduction in lateral direction, leading to ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$-based nanowires and nanoplatelets. Given that different values of the ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}{\mathrm{WS}}_{2}$ band offset have been reported, we show that the band offset determines the ordering of the energy levels in the valence band and spin projections at the $K$ point of the Brillouin zone. These variations as function of the value of the band offset are suppressed in an external electric field. For multilayer ${\mathrm{MoS}}_{2}/{\mathrm{WS}}_{2}$-based nanostructures, our calculations reveal nanowires and nanoplatelets with S-atom edges exhibit a metallic character, but nanowires with one S-atom and other Mo/W edge show the band gap with electrons located in ${\mathrm{MoS}}_{2}$ and holes in ${\mathrm{WS}}_{2}$ layer. The band gap can be controlled by the size of the nanowire in lateral direction and number of layers. The calculated real part of optical conductivity show that the lowest optical transitions originate from the optical transitions in ${\mathrm{MoS}}_{2}$ layers. The electronic structure is obtained from a parametrized tight-binding model that includes nonorthogonal ${sp}^{3}{d}^{5}$ orbitals and spin orbit coupling. Our results are gauged with respect to those extracted from density functional theory and $GW$ methods to ensure the high quality of our predictions.