Band-gap engineering and optoelectronic properties of 2D WSi2N4 nanosheets: A first principle calculations

The successful growth of centimeter-scale monolayer films of MoSi2N4 and WSi2N4 has attracted great interest (Science 369, 670, 2020). Here, we systematically investigate the effects of biaxial and uniaxial strain on the electronic structures of WSi2N4 nanosheets with different layers of monolayer(ML), bilayer(BL) and trilayer(TL), respectively, by using first-principles calculations. In addition, combined with the non-equilibrium Green’s function methods, the photoelectronic response of WSi2N4 ML is also explored. The results indicate that: 1) The biaxial and uniaxial strain can flexibly increase or decrease the band gap of WSi2N4 nanosheets. Particularly, tensile strain realizes the transition of WSi2N4 nanosheets from semiconductor to metal. 2) The tensile strain effectively improves the optical properties of WSi2N4 nanosheets in the visible light region, and the red/blue shift of the absorption peaks is observed in the optical spectrum by tensile/compressive strain. 3) The pin-junction photodiode of WSi2N4 ML generates sizeable photocurrents under illumination, showing a strong photoelectronic response to purple light. Furthermore, the biaxial tensile strain significantly enhances the photoelectric performance of the WSi2N4 photodiode and effectively modulates its detection range in the visible region. Hence, our findings suggest that WSi2N4 nanosheets are a promising multifunctional material for nanoelectronic and optoelectronic applications.