Investigating the layered structure of HfNBr and HfNCl0.5Br0.5: A DFT+U approach to optoelectronic and thermoelectric application

Abstract Layered materials have attracted considerable attention due to their distinctive properties. In this study, the optoelectronic and thermoelectric characteristics of HfNBr and its alloy with Cl, where Br atoms are partially replaced, were investigated using density functional theory (DFT), while incorporating the Hubbard correction (U) in the calculations. The structural and dynamic stability of these compounds was confirmed through cohesive energy and phonon results analysis. The electronic density of states (DOS) revealed semiconducting band gaps of 2.275 eV (using the GGA method) and 2.744 eV (with GGA+U) for HfNBr, while for the alloy HfNCl 0.5 Br 0.5 , the band gaps were calculated as 2.31 eV (GGA) and 2.781 eV (GGA+U). The highest optical conductivity was observed for pure HfNBr, reaching 6.519 × 10 15 s −1 at a photon energy of 5.03 eV along the x-direction, as calculated with GGA+U. For the alloy compound, the maximum optical conductivity was also along the x-direction, with a value of 5.549 × 10 15 s −1 at the same photon energy (5.03 eV), using the GGA+U method. Additionally, the peak absorption coefficient for HfNBr was found to be 3.348 × 10 8 m −1 at a photon energy of 4.91 eV using the GGA method. For the alloy, the maximum absorption coefficient, obtained using GGA+U, was 1.104 × 10 8 m −1 at a photon energy of 5.61 eV. At temperature of 300 K, corresponding to room temperature, the maximum of thermoelectric power factors per relaxation time for HfNBr and HfNCl 0.5 Br 0.5 were 60.82 × 10 16 μ W.m −1 .K −2 .s −1 at a chemical potential of −1.37 eV (GGA) and 58.38 × 10 16 μ W.m −1 .K −2 .s −1 at −1.56 eV (GGA+U), respectively. These findings provide valuable insights into the potential applications of these materials in optoelectronic and thermoelectric devices.