First‐principles investigation of the (HfSe2)4−n–(HfSSe)n (n = 0, 1, 2, 3, 4) lateral heterostructures

In this work, we investigate the structural, electronic, and optical properties of the HfSe2 and Janus HfSSe monolayers, and their lateral heterostructures (LHSs) (HfSe2)4−n–(HfSSe)n (n = 1, 2, and 3) using first‐principles calculations. Stability of these two‐dimensional (2D) materials is examined through phonon dispersion curves and cohesive energy. Besides, small heat of formation suggests the feasibility of experimental synthesis of the LHSs. Calculated electronic band structures indicate an indirect gap semiconductor nature of all materials at hand, where the energy gap decreases slightly from (HfSe2)4–(HfSSe)0 to (HfSe2)0–(HfSSe)4 as a result of the increase of Coulomb effect. Moreover, the LHSs formation makes possible the indirect–direct gap transition, which can be achieved by applying proper external strain to the lattice. Energy gap of the H22‐system shows a strong strain‐dependence, increasing with tensile strain and decreasing with compressive strain. The semiconductor–metal transition may be induced at strain strengths of −6% and −8%. Optical calculations indicate a wide absorption band from visible to ultraviolet regime with large absorption coefficient. Our findings introduce new 2D LHSs with tunable properties for application in optoelectronic nano devices. Atomic structure of (a) HfSe2, (b) HfSSe, and (c) Lateral (HfSe2)2‐(HfSSe)2 monolayer