Electronic properties of WS2 and WSe2 monolayers with biaxial strain: A first-principles study

Abstract In the present work, we consider electronic properties of WX 2 (X = S, Se) monolayers under a biaxial strain e b using the first principles study. Our calculations indicate that, at equilibrium, the WS 2 and WSe 2 monolayers are semiconductors with a direct band gap of respectively 1.800 eV and 1.566 eV while their bulk structures are indirect semiconductors. The electronic properties of the WX 2 monolayers are very sensitive with the biaxial strain, especially compression strain. The biaxial strain e b is the cause of the band gap of the WX 2 monolayers and especially the semiconductor-metal phase transition has occurred in the WS 2 monolayer at e b = - 10 % . In addition, the direct-indirect band gap transition was observed in both WS 2 and WSe 2 monolayers at a certain elongation of biaxial strain e b . The phase transitions in these monolayers can be very useful for their applications in nanoelectromechanical devices.