Zinc Oxide: Crystal Chemistry, Defect Physics, and Functional Applications

Abstract

Zinc oxide (ZnO) is a II-VI semiconductor with a direct band gap of approximately 3.37 eV and an exciton binding energy of 60 meV at room temperature. These properties, together with its chemical stability, non-toxicity, and earth-abundant composition, have made it the subject of sustained research over several decades. This review examines the structural and electronic properties of ZnO, with particular attention to native point defects and their role in n-type conductivity. We discuss the main synthesis routes, both physical and chemical, and describe how growth conditions govern grain morphology, oxygen stoichiometry, and carrier concentration. The review then surveys established and emerging application areas, including UV photodetection, piezoelectric transducers, gas sensing, photocatalysis, and dilute magnetic semiconductor behaviour following transition-metal doping. Where relevant, we note unresolved debates in the literature, such as the precise identification of donor species and the difficulty of achieving stable p-type ZnO. Representative references are drawn from peer-reviewed sources spanning the past three decades.