First-Principles Study of Adsorption of Reductive Gases (H₂, H₂S, NH₃) on a Transition Metal-Doped GaN Monolayer

This paper studies the adsorption energy, differential charge density, work function, energy band, density of states, optical properties, and recovery time of intrinsic GaN and transition metal Ni-doped GaN in adsorbing reducing gases H₂, H₂S, and NH₃ based on the first principles. The results show that the adsorption of H₂, H₂S, and NH₃ on the intrinsic GaN surface all belongs to physical adsorption. The adsorption of the three gases by Ni-doped GaN is all chemical adsorption, and the adsorption energies are -0.94, -1.45, and -1.41 eV, respectively, making the adsorption more stable. Ni doping enhances the charge transfer between the GaN surface and the gas, reducing the work function and bandgap width of the adsorption system. The maximum absorption coefficient of the doped system in the visible-light range is approximately 30% higher than that of the intrinsic GaN. The recovery times of Ni-doped GaN adsorbing H₂, H₂S, and NH₃ can be adjusted to 5.2, 3.4, and 7.2 s, respectively, by controlling the temperature. This study provides theoretical support for the detection and sensing of H₂, H₂S, and NH₃ gases based on GaN substrates.