Effect of biaxial strain on electronic and optical properties of vertically stacked HfS₂/HfSe₂ heterostructures

The structural, electronic, and optical properties of HfS2/HfSe2 heterostructures (HSs) have been investigated using Density Functional Theory. The HfS2 and HfSe2 monolayers with H and T phases with different stacking configurations were considered for the formation of HSs. HfS2(1T)/HfSe2(2H) is found to be the most stable HS as compared to other phases. All phases of HSs show indirect band-gaps HfS2(1T) (2.07 eV), HfSe2(2H) (1.63 eV), and HfS2(1T)/HfSe2(2H) (1.44 eV) with valence band (VB) of HS dominated by HfS2(1T) and the conduction band (CB) dominated by HfSe2(2H) leading to type-II configuration. The optical properties of HS show ab-sorption peaks in the visible region of 420-430 nm with an absorption coefficient of 1.82-1.89 x 10(5) cm(-1). Further, the stability of the HS increases with tensile strain and decreases with compressive strain. Similarly, the band gap increases from 1.44 eV to 1.51 eV with the tensile strain and decreases to 1.30 eV with compressive strain. The tunability of electronic band gap and band alignment of Hf-based HSs by external strain makes them useful for possible use in futuristic optoelectronic devices.