Stability and optoelectronic properties of HfS2/HfSe2 heterostructures under tensile strain: A first-principles study

Abstract

The optoelectronic properties of monolayer HfS2, HfSe2, and HfS2/HfSe2 heterostructures under biaxial strain were calculated using density functional perturbation theory (DFPT). The heterostructure formed by monolayer HfS2 and HfSe2 undergoes a transition from an indirect to a direct bandgap. Additionally, under biaxial tensile strain, the bandgaps of all systems exhibit a linear increase. The stability of the structures was further verified by calculating the phonon spectra. Monolayer HfS2 and HfSe2 exhibited imaginary frequencies at a biaxial strain of 8%, whereas the HfS2/HfSe2 heterostructure displayed an imaginary frequency at a strain of 6%. This suggests that the structures have reached their maximum load-bearing limit and lost stability. The van der Waals interactions between the layers of the heterostructure had minimal influence in the x–y plane, but they could induce interlayer tearing in the vertical direction, resulting in an earlier loss of stability compared to the monolayer structures. The optical absorption and reflectance properties of the three systems under strain were also calculated. A blue shift was observed in the low-energy region, while a significant red shift was observed in the high-energy region. The two-dimensional heterostructure exhibited significantly improved absorption coefficients and reflectance in the high-energy region compared to the two monolayer structures.