First-principles study of the effects of interstitial H and point vacancies on the photocatalytic performance of Be/Mg/Ca-doped GaN

Abstract

The effects of Be/Mg/Ca doping on the optical properties of GaN have been widely investigated experimentally and theoretically. However, metalorganic chemical vapor deposition and vacuum coating methods are used in the experiments, and interstitial H is difficult to remove in GaN. The effects of Be/Mg/Ca doping and interstitial H coexistence with Ga vacancy on the photocatalytic performance of GaN are rarely explored in a vacuum environment. This study examines the formation energy and electronic structure of Ga34MN36 (M = Be/Mg/Ca) and Ga34MHiN36 (M = Be/Mg/Ca) systems and the main factors affecting their photocatalytic performance by using the generalized gradient approximation plane wave ultrasoft pseudopotential + U method within the framework of density functional theory. Results show that the formation energy of the Ga34MN36 (M = Be/Mg/Ca) and Ga34MHiN36 (M = Be/Mg/Ca) systems are greater under Ga-rich conditions than under N-rich conditions, indicating that both doping systems are more readily formed and have a more stable structure under N-rich conditions than under Ga-rich conditions. The visible light effect, electric dipole moment, effective mass, and oxidation–reduction reaction affecting the photocatalytic performance of the doping systems were analyzed. Compared with the Ga34MN36 (M = Be/Mg/Ca) system, the Ga34CaHiN36 system shows a more obvious red-shift in the absorption spectrum, a larger absorption spectrum intensity, a better carrier activity, a faster carrier separation rate, a longer carrier lifetime, and a stronger oxidation ability. These results suggest that the Ga34CaHiN36 system is an excellent photocatalyst that can be utilized in designing and preparing novel GaN photocatalysts.