Since the discovery of graphene, 2D layered materials have sustained a surge in research interest. Researchers have focused on those with high carrier mobility and other unique electronic and optical properties, which may help realize future nanoelectronics and optoelectronic devices.

To bring these materials one step closer to applications, Wu et al. investigated ways to engineer the band structure in molybdenum and tungsten nitride bilayered films (MoSi2N4-WSi2N4) via the application of biaxial strain and external electric fields.

Based on their density functional theory calculations, the authors present the impact of compressive and tensile strain on the band gap of the material. They found that compressive strain changes the bond length and can result in a transition from indirect to direct band gap, which is important for optoelectronic applications.

The authors also discovered a semiconductor-to-metal transition with the application of an external electric field, where the band gap in the WSi2N4 layer was reduced from 1.94 eV down to 0 eV when the electric field reached 6 V/nm.

“We show that the biaxial strain and external electric field are effective ways to modulate MoSi2N4 and WSi2N4 bilayers,” said author Qingyun Wu.

MoSi2N4-WSi2N4 bilayered films have been shown to represent a milestone in monolayer preparation of non-micaceous materials, as recent experimental reports demonstrate that they can be prepared as high quality layers using chemical vapour deposition. This study provides insights into the band structure engineering of these tunable materials for potential use in next-generation nanoelectronic and optoelectronic applications.

Source: “Semiconductor-to-metal transition in bilayer MoSi2N4 and WSi2N4 with strain and electric field,” by Qingyun Wu, Liemao Cao, Yee Sin Ang, and Lay Kee Ang, Applied Physics Letters (2021). The article can be accessed at