Computational prediction of stable semiconducting Zn-C binary compounds

Abstract

Elemental carbon has been successfully used to tune the light emission properties of zinc oxide (ZnO) through artificially doping but the underlying mechanism remains controversial. At present, carbon-related defect complexes are the main explanation. Nevertheless, the possibility of forming semiconducting Zn-C compounds has not been discussed. In this study, we reveal the existence of various stable semiconducting Zn-C compounds. Based on particle swarm optimization and first-principles calculations, we perform a structural search of Zn-C binary compounds and report four stable semiconducting structures, in which the covalent Zn-C bonding characteristics are stronger compared with that in the metal rocksalt zinc carbide (ZnC). Crucially, three of the four Zn-C compounds have direct or quasi-direct band gaps in the range of 1.09–2.94 eV which are energies highly desirable for optoelectronic applications. Electronic transitions across the band gaps of these Zn-C structures could contribute to blue and near-infrared light emissions of C-doped ZnO. Our results have not only unraveled a new perspective to explain and tailor the light emission properties of ZnO but also provide a deeper understanding of possible Zn-C compounds.