Strain dependences of electronic properties, band alignments and thermal properties of bilayer WX2 (X = Se, Te)

Abstract

ABSTRACT We presented a comprehensive study of electronic properties and phonon thermal transport properties in layered WX2 (X = Se, Te) using first-principles calculations combined with density functional perturbation theory (DFPT). Our results indicated that the spin–orbit coupling (SOC) and biaxial strains have significant effects on the band gaps and band alignments of the bilayer WX2 (X = Se, Te), and the d-orbital of the W atom played a dominant role at the valence and conduction band edge positions. We found that the band gaps decreased with the increase of strain and WTe2 have the transition from indirect band gap to direct band gap at 2% strain. We also calculated their lattice thermal conductivities , group velocities, cumulative thermal conductivities along the x and y directions, and scattering rates at room temperature. The calculated along x and y directions of WSe2 are 70.81 and 78.38 W/m K, respectively, whereas those of WTe2 were relatively low (55.05 W/m K along x-direction and 59.97 W/m K along y-direction), which mainly originated from their relatively smaller phonon group velocities and atomic weights. Two materials exhibited that , and group velocities in the y-direction were higher than those in the x-direction. We also investigated the size dependence of the and contributions of different acoustic and optical branches to the total . It was found that the nanostructure may be efficient to reduce .