First-Principles Study of Band Gap Engineering in Doped ZnO Nanostructures for Optoelectronic Applications

Abstract

Zinc oxide (ZnO) is a wide band gap semiconductor with strong potential for ultraviolet (UV) optoelectronic devices. However, its limited visible light absorption restricts broader applications. In this study, density functional theory (DFT) was employed to investigate the effects of doping ZnO nanostructures with transition metals (Mn, Co, and Ni) on their structural and electronic properties. The results revealed that doping induced significant modifications in electronic band structures, with band gap narrowing from 3.2 eV (pristine ZnO) to as low as 2.1 eV in Mn-doped systems. Density of states analysis confirmed enhanced hybridization between Zn 3d, O 2p, and dopant d-orbitals, leading to mid-gap states favorable for visible light absorption. Optical property simulations indicated improved absorption coefficients in the 400–700 nm region, making doped ZnO promising for solar-driven devices. Charge density analysis demonstrated strong covalent interactions between dopant atoms and oxygen, contributing to structural stability. The findings provide theoretical insights for tailoring ZnO through doping strategies, guiding experimental design of efficient optoelectronic and photocatalytic materials.