Tuning the band alignment and electronic properties of XSe2/WSi2N4 (X=Mo,W) van der waals heterostructures with high carrier mobility

We investigate the electronic structure and optoelectronic properties of XSe2/WSi2N4 (X = Mo, W) van der Waals heterostructures (vdWHs) based on the first-principles calculations. The MoSe2(WSe2)/WSi2N4 vdWHs exhibit semiconductor properties with the direct bandgap of 1.26 (1.16) eV and type-Ⅰ band alignment, which have potential applications in light-emitting diodes and quantum-well lasers. The hole carrier mobility of vdWHs reaches the order of 104, which is much better than that of isolated layers, and the carrier mobility of WSe2/WSi2N4 vdWH is better overall than that of MoSe2/WSi2N4 vdWH. Furthermore, The XSe2/WSi2N4 vdWHs exhibit a wide absorption range from the visible to the ultraviolet and better optical absorption than isolated layers. Besides, the interlayer coupling, biaxial strain and external electric fields (Eex) allows flexible adjustment of the electronic structure and the type of band alignment of the XSe2/WSi2N4 vdWHs. In particular, Eex allows the vdWHs to achieve the band alignments of type-Ⅰ, type-Ⅱ and type-Ⅲ and the transitions of the direct-indirect bandgap. Our results demonstrate the great potential of the XSe2/WSi2N4 vdWHs for applications in optoelectronic devices.