Theoretical and Experimental Investigations on Effects of Native Point Defects and Nitrogen Doping on the Optical Band Structure of Spinel ZnGa2O4

Impurity states in semiconductors are so important for optical related properties that understanding the role of native and imported defects is essential to design highly active semiconductors. Here, the structural and electronic properties of ZnGa2O4 with native atomic substitution, oxygen vacancies, and imported N doping are first investigated by first-principles calculations. It is demonstrated that native atomic substitution is energetically unfavorable and the most stable existence forms for N doping and O vacancies are N1– and O2+ states in most cases under various chemical environments. The band structures and density of states reveal that the photochemical property is significantly enhanced only by 2Ns doping with a great increase of valence band maximum relative to the Fermi level, whereas single-N atom doping or import of O vacancies or simultaneous import of N doping and O vacancies just generates impurity states in the band gaps. Moreover, experimental characterizations including X-ray photoelectron spectroscopy and diffuse reflectance spectroscopy spectra confirm the above theoretical results, and optical calculations further illustrate the effects of defects for light absorption. Our results will be helpful to understand the effects of native point defects and external nitrogen doping on spinel ZnGa2O4 and design its band gap with desired optical properties.